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Do different disparity proxies converge on a common signal? Insights from the cranial morphometrics and evolutionary history of Pterosauria (Diapsida: Archosauria)
Abstract
Disparity, or morphological diversity, is often quantified by evolutionary biologists investigating the macroevolutionary history of clades over geological timescales. Disparity is typically quantified using proxies for morphology, such as measurements, discrete anatomical characters, or geometric morphometrics. If different proxies produce differing results, then the accurate quantification of disparity in deep time may be problematic. However, despite this, few studies have attempted to examine disparity of a single clade using multiple morphological proxies. Here, as a case study for this question, we examine the disparity of the volant Mesozoic fossil reptile clade Pterosauria, an intensively studied group that achieved substantial morphological, ecological and taxonomic diversity during their 145+ million-year evolutionary history. We characterize broadscale patterns of cranial morphological disparity for pterosaurs for the first time using landmark-based geometric morphometrics and make comparisons to calculations of pterosaur disparity based on alternative metrics. Landmark-based disparity calculations suggest that monofenestratan pterosaurs were more diverse cranially than basal non-monofenestratan pterosaurs (at least when the aberrant anurognathids are excluded), and that peak cranial disparity may have occurred in the Early Cretaceous, relatively late in pterosaur evolution. Significantly, our cranial disparity results are broadly congruent with those based on whole skeleton discrete character and limb proportion data sets, indicating that these divergent approaches document a consistent pattern of pterosaur morphological evolution. Therefore, pterosaurs provide an exemplar case demonstrating that different proxies for morphological form can converge on the same disparity signal, which is encouraging because often only one such proxy is available for extinct clades represented by fossils. Furthermore, mapping phylogeny into cranial morphospace demonstrates that pterosaur cranial morphology is significantly correlated with, and potentially constrained by, phylogenetic relationships.
... This indicates that disparity was not likely saturated by the end of the time span sampled here, and these trends of increase may continue in the Cretaceous. Similar delayed disparity peaks have been previously found for pterosaurs (Prentice et al., 2011;Butler et al., 2012;Foth et al., 2012), crocodylomorphs (Stubbs et al., 2021), and turtles (Foth and Joyce, 2016;Foth et al., 2017), but contrast with many smaller clades (see below). In contrast, concordant with our results for rates of change through time (see Discussion below), Archosauromorpha as a whole and all of the subclades examined (see specific points for Dinosauria, below) show broadly decreasing average displacement through time, indicating that evolutionary change tended to tail off after the initial radiation of novel ecomorphologies, concordant with an "early burst" pattern of evolution sensu lato (Puttick, 2018). ...
... In contrast, the cranial disparity of pterosaurs through time differs considerably from the results of Foth et al. (2012). This is not unexpected, however, because the latter study used only terminal taxa and an epoch-level coarse temporal binning instead of the stages used here. ...
... This is not unexpected, however, because the latter study used only terminal taxa and an epoch-level coarse temporal binning instead of the stages used here. Nevertheless, the current study does reveal a small disparity peak at the end of the Late Triassic and a higher one at the end of the Late Jurassic, which broadly reflect the signal obtained by Foth et al. (2012). However, the latter study, due to its coarseness, misses an intermediate period of disparity depression between these peaks during the Early and Middle Jurassic. ...
Adaptive radiations have played a major role in generating modern and deep-time biodiversity. The Triassic radiation of the Archosauromorpha was one of the most spectacular vertebrate radiations, giving rise to many highly ecomorphologically varied lineages—including the dinosaurs, pterosaurs, and stem-crocodylians—that dominated the larger-bodied land fauna for the following 150 Ma, and ultimately gave rise to today’s > 10,000 species of birds and crocodylians. This radiation provides an outstanding testbed for hypotheses relating to adaptive radiations more broadly. Recent studies have started to characterize the tempo and mode of the archosauromorph early adaptive radiation, indicating very high initial rates of evolution, non-competitive niche-filling processes, and previously unrecognized morphological disparity even among non-crown taxa. However, these analyses rested primarily either on discrete characters or on geometric morphometrics of the cranium only, or even failed to fully include phylogenetic information. Here we expand previous 2D geometric morphometric cranial datasets to include new taxa and reconstructions, and create an analogous dataset of the pelvis, thereby allowing comparison of anatomical regions and the transition from “sprawling” to “upright” posture to be examined. We estimated morphological disparity and evolutionary rates through time. All sampled clades showed a delayed disparity peak for sum of variances and average nearest neighbor distances in both the cranium and pelvis, with disparity likely not saturated by the end of the studied time span (Late Jurassic); this contrasts with smaller radiations, but lends weight to similar results for large, ecomorphologically-varied groups. We find lower variations in pelvic than cranial disparity among Triassic-Jurassic archosaurs, which may be related to greater morphofunctional constraints on the pelvis. Contrasting with some previous work, but also confirming some previous findings during adaptive radiations, we find relatively widespread evidence of correlation between sampled diversity and disparity, especially at the largest phylogenetic scales and using average displacement rather than sum of variances as disparity metric; this also demonstrates the importance of comparing disparity metrics, and the importance of phylogenetic scale. Stem and crown archosauromorphs show a morphological diversification of both the cranium and pelvis with higher initial rates (Permian–Middle Triassic and at the base of major clades) followed by lower rates once diversification into niches has occurred (Late Triassic–Jurassic), indicating an “early burst” pattern sensu lato. Our results provide a more detailed and comprehensive picture of the early archosauromorph radiation and have significant bearing on the understanding of deep-time adaptive radiations more broadly, indicating widespread patterns of delayed disparity peaks, initial correlation of diversity and disparity, and evolutionary early bursts.
... Any study of morphological disparity first requires a quantification of morphology with various proxies of morphology acting as the data. The most commonly used morphological proxies are discrete character matrices and geometric morphometric data sets (Foth, Brusatte & Butler, 2012;Hetherington et al., 2015). Analyses of discrete character data seem to be the most common (e.g. ...
... Analyses of discrete character data seem to be the most common (e.g. Foote, 1994;Wills et al., 1994;Wills, 1998;Ciampaglio, Kemp & McShea, 2001;Brusatte et al., 2008Brusatte et al., , 2011Brusatte et al., , 2014Young et al., 2010;Butler et al., 2012;Wills et al., 2012;Marx & Fordyce, 2015), potentially due to the wide availability of phylogenetic data sets. Each morphological proxy has its advantages and disadvantages. ...
... Yet, with this method it is difficult to encompass the morphology of the entire organism, and choice of which aspects to quantify and landmarking scheme remain subjective. Despite the fundamental differences between these morphological proxies, studies have shown little difference in patterns revealed by discrete character and morphometric methods (Villier & Eble, 2004;Foth et al., 2012;Hetherington et al., 2015). ...
Crocodyliforms are traditionally considered a morphologically conservative group, retaining a similar body plan and small range of cranial morphologies throughout their evolutionary history. This qualitative assessment ignores many extinct highly divergent groups. Here the author employs geometric morphometric methods to characterize the crania of 131 extant and extinct crocodyliforms and track changes in disparity and morphospace occupation through time (Early Jurassic–Recent). The data were phylogenetically corrected using a novel method based on squared change parsimony. Cranial disparity peaked in the Late Cretaceous followed by a dramatic decline into the earliest Paleogene. This decline matches in neither timing nor magnitude with changes in diversity, and is not directly related to the end-Cretaceous mass extinction. The decline was partly driven by the evacuation of the region of morphospace exemplified by a short, narrow snout – a morphotype never explored by crown-group crocodylians. The Cretaceous peak in range-based disparity metrics is largely driven by the radiation of the bizarre notosuchians and their exclusion from the data set brings Cretaceous disparity closer in-line with Jurassic and Cenozoic levels. However, the peak remains in variance-based metrics, suggesting the high average dissimilarity between forms during this time period is not driven by this clade alone. Modern crocodylian disparity is low relative to Cretaceous levels, but is similar to Jurassic levels.
... As a rigorous assessment of diversity through time remains untenable until the alpha taxonomy and phylogeny of fossil turtles have been established, we here present a global analysis of turtle cranial disparity, a measure that assesses morphological diversity as opposed to taxonomic diversity [36][37][38]. Among tetrapods, this metric has most recently been applied, among others, to the cranial evolution in pterosaurs [39], crurotarsans [40] and theropod dinosaurs [41], but this method remains to be applied to turtles. In addition to providing a first estimate of turtle disparity through time, we here highlight the most notable disparity trends, investigate differences in disparity between the two primary clades of turtles-Pan-Cryptodira and Pan-Pleurodira-and discuss the primary factors that may have contributed to apparent differences and trends. ...
... A slow, steady increase of disparity in concert with a slow build-up of diversity, as opposed to an explosive, early increase of either, is indicative of the concordant evolution of these two diversity measures [68]. Delayed peaks of disparity have otherwise been found for pterosaurs [39,60,69,70] and the dentition of ungulates [71] and carnivoramorphan mammals [72], but most other animal groups previously investigated reach their maximum disparity early in evolution [68,73,74]. Global climate reconstructions point towards a gradual rise in temperatures from the Jurassic to the Palaeocene [66,67], which generally correlates with our observed increase in disparity within the same time window. ...
... Our study only investigates the cranial disparity of turtles, but it is unclear whether the trends we discerned are unique to the cranium or representative for other anatomical systems. The two previous studies that investigated this issue for echinoid [91] and pterosaurs [39] concluded that different morphological proxies and body regions produce similar temporal disparity curves through time. However, given that the turtle shell remains highly conserved throughout turtle evolution in regards to the arrangement and number of bones and scutes and that the shape is strongly constrained by ecological factors, we speculate that the postcranial system may yield different trends in turtles [92]. ...
Turtles (Testudinata) are a diverse group of amniotes that have a rich fossil record that extends back to the Late Triassic, but little is known about global patterns of disparity through time.We here investigate the cranial disparity of 172 representatives of the turtle lineage and their ancestors grouped into 20 time bins ranging from the Late Triassic until the Recent using two-dimensional geometric morphometrics. Three evolutionary phases are apparent in all three anatomical views investigated. In the first phase, disparity increases gradually from the Late Triassic to the Palaeogene with only a minor perturbation at the K/Textinct event. Although globalwarming may have influenced this increase, we find the Mesozoic fragmentation of Pangaea to be a more plausible factor. Following its maximum, disparity decreases strongly towards the Miocene, only to recover partially towards the Recent. The marked collapse in disparity is likely a result of habitat destruction caused by global drying, combined with the homogenization of global turtle faunas that resulted from increased transcontinental dispersal in the Tertiary. The disparity minimum in the Miocene is likely an artefact of poor sampling.
... Studies involving geometric morphometrics analysis of these structures are scarce (e.g. Prentice et al. 2011;Foth et al. 2012). The Anhangueridae are diagnosed by the presence of sagittal bone crests located in the premaxilla and jaw, distal expansion of the premaxilla and dentary and some postcranial features (Kellner and Tomida 2000). ...
... Despite the absence of complete specimens referred to A. santanae,we have conducted an additional analysis with the skull reconstruction proposed by Wellnhofer (1991). The use of reconstructions in geometric morphometric analysis has been previously done in pterosaurs (Foth et al. 2012) and dinosaurs ). Foth et al. (2012 focused their analysis in cranial reconstructions because the great majority of preserved pterosaur skull is crushed or incomplete. ...
... not preserve their sagittal premaxillary crest. Despite the absence of complete specimens referred to A. santanae,we have conducted an additional analysis with the skull reconstruction proposed by Wellnhofer (1991). The use of reconstructions in geometric morphometric analysis has been previously done in pterosaurs (Foth et al. 2012) and dinosaurs ). Foth et al. (2012 focused their analysis in cranial reconstructions because the great majority of preserved pterosaur skull is crushed or incomplete. The ontogenetic stage of all taxa used here is described in Table 1. ...
Sagittal cranial crests are evident in several groups of pterosaurs, although their exact function has still not been determined. One of the most distinctive features of the Anhangueridae is a sagittal premaxillary crest on the anterior portion of the skull. A comparison of the skulls of anhanguerids revealed that they all have similar skull and crests shapes. In this paper, six anhanguerids from Araripe Basin were analysed using bidimensional geometric morphometrics. As a result, the taxa were arranged in two groups and two isolated taxa in the morphospace: elongated skulls, with crests high and expanded, representing 40% of the skull length; and median size skulls; and low and short crests starting posteriorly on the region of the seventh and fourth pairs of alveoli. Some of these groupings also share a phylogenetic relationship. Despite this separation in morphospace, the difference between the morphology of the crest was not as striking as in other pterodactyloid pterosaurs. Crest variation in Anhangueridae presented in this paper is considered as non-specific, with some patterns of similarity, such as the shape and the beginning of this structure on the premaxilla. In addition, the presence of positive allometric growth in the skull was observed and no trend in sexual dimorphism could be pointed.
... As a result, the teeth are close to each other in the largest specimens only (Figs 4C, D, 5E, K, M, Q, S-U), and the distance between the alveoli can be larger in smaller individuals (Figs 4K, L, 5D, H, I). Many studies show a high variability in the morphology of the rostrum in Crocodyloidea, whether related to sexual dimorphism (Foth et al. 2012) or ontogeny (Mook 1921b;Erickson et al. 2003;Foth et al. 2012). Gavialis gangeticus also shows a reduction in the distance between alveoli in the same row during growth. ...
... As a result, the teeth are close to each other in the largest specimens only (Figs 4C, D, 5E, K, M, Q, S-U), and the distance between the alveoli can be larger in smaller individuals (Figs 4K, L, 5D, H, I). Many studies show a high variability in the morphology of the rostrum in Crocodyloidea, whether related to sexual dimorphism (Foth et al. 2012) or ontogeny (Mook 1921b;Erickson et al. 2003;Foth et al. 2012). Gavialis gangeticus also shows a reduction in the distance between alveoli in the same row during growth. ...
This study, based on previously undescribed crocodylian remains from the Lower Miocene of the Bugti Hills (Balochistan, Pakistan), identifies at least three distinct species. It confirms the validity of the species initially identified as ‘ Gavialis ’ pachyrhynchus , establishing it as the sister taxon to the massive Miocene crocodylian Rhamphosuchus crassidens . Consequently, it is reclassified as Rhamphosuchus pachyrhynchus . Additionally, ‘ Gharialis ’ curvirostris is now acknowledged as a valid species under the new genus name Pseudogavialis , closely related to Gavialis . Another set of remains represents a third species, although the poor preservation hinders precise identification. The phylogenetic relationship between Tomistoma and Gavialis is one of the most debated issues in crocodylian phylogeny. Molecular analyses suggest a sister‐taxa relationship dating back to the Early Miocene, while morphological analyses place Gavialis at the base of the tree, diverging from ‘thoracosaurs’, with a Gavialoidea–Crocodyloidea split in the Cretaceous. The inclusion of newly described species in phylogenetic analyses yields variable outcomes, highlighting the sensitivity of results to the species considered. The insertion of Portugalosuchus azenhae , found as a ‘thoracosaur’, aligns with traditional morphological findings, while the inclusion of Indo‐Pakistani species of Rhamphosuchus supports the molecular hypothesis. Nevertheless, the large number of morphological gavialoids and ‘thoracosaurs’ makes the molecular result strongly stratigraphically incongruent. The inclusion of fossil species in the phylogenetic analyses significantly impacts our understanding of crocodylian relationships. Even when molecular results align with morphological data, the persistent stratigraphic incongruence does not resolve the Gavialis – Tomistoma dilemma.
... Spatial landmark analysis is precluded at high taxonomic rank such as phylum because, by definition, phyla share few morphological homologies. Discrete characters provide a suitable alternative given that there are no practical limits to their scalability (2, 3), and comparative analyses have shown that continuous and discrete character datasets can capture the same phenomenon (11)(12)(13)(14). The use of discrete characters produces results that have nonmetric properties (15-17), but this approach can and has been used to elucidate broad patterns of similarities and clustering within multidimensional space (18), particularly in formulating the hyoptheses we seek to test. ...
... Spatial landmark analysis is precluded at high taxonomic rank such as phylum because, by definition, phyla share few morphological homologies. Discrete characters provide a suitable alternative given that there are no practical limits to their scalability (2, 3), and comparative analyses have shown that continuous and discrete character datasets can capture the same phenomenon (11)(12)(13)(14). The use of discrete characters produces results that have nonmetric properties (15)(16)(17), but this approach can and has been used to elucidate broad patterns of similarities and clustering within multidimensional space (18), particularly in formulating the hyoptheses we seek to test. ...
Significance
We attempt to quantify animal “bodyplans” and their variation within Metazoa. Our results challenge the view that maximum variation was achieved early in animal evolutionary history by nonuniformitarian mechanisms. Rather, they are compatible with the view that the capacity for fundamental innovation is not limited to the early evolutionary history of clades. We perform quantitative tests of the principal hypotheses of the molecular mechanisms underpinning the establishment of animal bodyplans and corroborate the hypothesis that animal evolution has been permitted or driven by gene regulatory evolution.
... [34][35][36]), functionally relevant measurements and ratios [37,38] and discrete descriptive characters [20,39,40]. Previous pterosaur disparity studies have been conducted, which assessed disparity of the skull with geometric landmarks [41], skeletal disparity based on discrete characters [2] and ecomorphological variation using continuous and discrete cranial characters [20], but mandible shape has never been considered. Mandibular disparity has been the focus of studies exploring ecomorphological and functional variation in a macroevolutionary context [13,42], early tetrapods [43], mammals [17], crurotarsans [35] and dinosaurs [18]. ...
... Our sample size and scope are comparable with previous disparity studies (e.g. [41]). Individual specimens were used to represent each taxon, and lateral jaw images were sourced during collection visits and from figures and reconstructions in the literature (see electronic supplementary material). ...
Pterosaurs were a successful group of Mesozoic flying reptiles. They were the first vertebrate group to achieve powered flight and varied enormously in morphology and ecology, occupying a variety of niches and developing specialized feeding strategies. Ecomorphological principles suggest this variation should be reflected by great morphological diversity in the lower jaw, given that the mandible served as the primary apparatus for prey acquisition. Here we present the first study of mandibular shape disparity in pterosaurs and aim to characterize major aspects of variation. We use a combination of geometric morphometric approaches, incorporating both outline analysis using elliptical Fourier analysis and semi-landmark approaches. Our results show that morphological convergence is prevalent and many pterosaurs, belonging to diverse dietary groups and subclades, overlap in morphospace and possessed relatively simple 'rod-shaped' jaws. There is no clear trend of size distributions in pterosaur mandibular morphospace, and larger forms are widely distributed. Additionally, there is limited functional signal within pterosaur lower jaw morphospace. Instead, the development of a large anterior ventral crest represents the major component of disparity. This suggests that a socio-sexual trait was a key driver for innovation in pterosaur lower jaw shape.
... Only very recently have researchers started investigating whether different disparity metrics reveal common signals (Villier and Eble 2004;Anderson and Friedman 2012;Foth et al. 2012;Hetherington et al. 2015;Mongiardino Koch et al. 2017). Nearly all studies showed positive correlations between the various methods, but the strength of the correlations differs for each comparison of methods (Villier and Eble 2004;Anderson and Friedman 2012;Foth et al. 2012;Hetherington et al. 2015). ...
... Only very recently have researchers started investigating whether different disparity metrics reveal common signals (Villier and Eble 2004;Anderson and Friedman 2012;Foth et al. 2012;Hetherington et al. 2015;Mongiardino Koch et al. 2017). Nearly all studies showed positive correlations between the various methods, but the strength of the correlations differs for each comparison of methods (Villier and Eble 2004;Anderson and Friedman 2012;Foth et al. 2012;Hetherington et al. 2015). Contradictory to this, Mongiardino Koch et al. (2017) found contrasting patterns when comparing landmark and discrete character data. ...
For years, palaeobiologists have studied the broad patterns of evolution simply by species counting. Now a revolution is underway, with richer data about novelties and their role in evolution being used. The diversity of form and function of organisms, their disparity, is studied in many different ways and using many very different methods. Disparity studies have become quite common, but few comparisons have been made between the different disparity metrics. Here we provide the first large scale test for congruence between three methods of capturing morphological disparity, discrete characters, morphometric outlines and geometric morphometric landmarks, using theropod mandibles as our case study. We find that all methods have a significant correlation with each other. The correlation is strongest between the two morphometric methods, showing r-values ranging between 0.69 and 0.81, and much weaker between the morphometric methods and the discrete characters, with r-values between 0.27 and 0.43. We also deduce macroevolutionary patterns from the disparity results, including but not limited to the Oviraptorosauria showing the highest disparity of all theropods, and disparity being lowest in the Late Triassic and highest in the Late Cretaceous, as might be expected within a long-term evolving and diversifying clade.
... Thus, the Kungurian peak can be interpreted as delayed or late saturation of morphospace by captorhinids. A similar late peak in disparity has, for example, also been found in blastoids 63 and trilobites 64,65 among invertebrates and pterosaurs among vertebrates 66 . ...
... However, a study of the radiation of the echinoid order Spatangoida empirically demonstrated that, independent of the choice of taxonomic rank (species or genera) and different disparity proxies such as landmarks, traditional morphometrics, and discrete characters, in the end all methods led to the same signal and general trend through time 7 . This was further supported in vertebrates by a study of pterosaur disparity, with different sources of morphological data providing congruent disparity results 66 . ...
The relationship between diversity and disparity during the evolutionary history of a clade provides unique insights into evolutionary radiations and the biological response to bottlenecks and to extinctions. Here we present the first comprehensive comparison of diversity and disparity of captorhinids, a group of basal amniotes that is important for understanding the early evolution of high-fiber herbivory. A new fully resolved phylogeny is presented, obtained by the inclusion of 31 morphometric characters. The new dataset is used to calculate diversity and disparity through the evolutionary history of the clade, using both discrete and continuous characters. Captorhinids do not show a decoupling between diversity and disparity, and are characterized by a rather symmetric disparity distribution, with a peak in occupied morphospace at about the midpoint of the clade's evolutionary history (Kungurian). This peak represents a delayed adaptive radiation, identified by the first appearance of several high-fiber herbivores in the clade, along with numerous omnivorous taxa. The discrete characters and continuous morphometric characters indicate the same disparity trends. Therefore, we argue that in the absence of one of these two possible proxies, the disparity obtained from just one source can be considered robust and representative of a general disparity pattern.
... Therefore, a longlasting question in disparity-based studies is whether or not the patterns captured by discrete and morphometric variables are congruent. Surprisingly, so far attempts at answering this question have unanimously concluded that the patterns derived from both types of data are compatible (Villier & Eble, 2004;Anderson & Friedman, 2012;Foth et al., 2012;Hetherington et al., 2015). This result is especially intriguing given the fact that palaeontological and neontological approaches seem to offer opposite views on some key evolutionary questions, such as the relative frequency of 'early bursts' of phenotypic evolution (Slater & Pennell, 2013). ...
... Where previous studies have systematically found congruence (Villier & Eble, 2004;Anderson & Friedman, 2012;Foth et al., 2012;Hetherington et al., 2015), we found strong evidence of disagreement. Patterns of morphospace occupation, as derived from a discrete and a morphometric data set, were significantly different under a permutation test, thus revealing that the observed variables cannot be partitioned in a way that results in larger differences. ...
Many paleontological studies have investigated the evolution of entire body plans, generally relying on discrete character-taxon matrices. In contrast, macroevolutionary studies performed by neontologists have mostly focused on morphometric traits. Although these data types are very different, some studies have suggested that they capture common patterns. Nonetheless, the tests employed to support this claim have not explicitly incorporated a phylogenetic framework, and may therefore be susceptible to confounding effects due to the presence of common phylogenetic structure. We address this question using the scorpion genus Brachistosternus Pocock 1893 as case study. We make use of a time-calibrated multilocus molecular phylogeny, and compile discrete and traditional morphometric datasets, both capturing the overall morphology of the organisms. We find that morphospaces derived from these matrices are significantly different, and that the degree of discordance cannot be replicated by simulations of random character evolution. Moreover, we find strong support for contrasting modes of evolution, with discrete characters being congruent with an ‘early burst’ scenario while morphometric traits suggest species-specific adaptations to have driven morphological evolution. The inferred macroevolutionary dynamics are therefore contingent on the choice of character type. Finally, we confirm that metrics of correlation fail to detect these profound differences given common phylogenetic structure in both datasets, and that methods incorporating a phylogenetic framework and accounting for expected covariance should be favored.
... Mathematically, a cladisto-space is an n dimensional object that summarises the cladistic distances between the taxa present in a cladistic matrix (see details below). Although empirically inter-taxon distances are the same in a morphospace or a cladisto-space (Foth et al., 2012;Hetherington et al., 2015), we prefer the term cladistospace to make it clear that this space is estimated using cladistic data and not morphometric data and because both objects have slightly different properties. For example, because of its inherent combinatory properties, a cladisto-space is a finite theoretical object limited by the product of the number of character states, whereas a morphospace is an infinite theoretical object. ...
... Furthermore, empirical studies have shown that the same signal seems to be captured when using either geometric morphometric or cladistic methods to describe disparity (Foth et al., 2012;Hetherington et al., 2015). ...
... Despite the morphological similarities between pterygotid species, their ecological roles range from a more generalized strategy in more basal eurypterids (Erettopterus), to highlevel active predation (Jaekelopterus, Pterygotus and IVPP- 14593) and specialized ambush predation or scavenging, perhaps in low light (Acutiramus). Previous studies [5] [9] on the ecological role of pterygotids have been driven, in part, by debates on clade selection [18] [19] and clade interaction, primarily via competitive replacement [20] [21]. Competitive replacement has been suggested to have played a role in the evolution of eurypterids and jawless fish [17] but this hypothesis has been largely dismissed [22]. ...
... Cladistic character data have been shown to converge on a common signal with other forms of morphometric data, e.g. morphological landmarks [18] [19], but it has also been suggested that cladistically derived distance matrices may underrepresent functional diversity [20]. In order to fully capture morphological variation in pterygotid chelicerae ten discrete morphological characters were added to the eight cheliceral characters from the phylogenetic matrix (characters describing other aspects of the morphology of the pterygotid taxa were not included). ...
Pterygotid eurypterids have traditionally been interpreted as active, high-level, visual predators; however, recent studies of the visual system and cheliceral morphology of the pterygotid Acutiramus contradict this interpretation. Here, we report similar analyses of the pterygotids Erettopterus, Jaekelopterus and Pterygotus, and the pterygotid sister taxon Slimonia. Representative species of all these genera have more acute vision than A. cummingsi. The visual systems of Jaekelopterus rhenaniae and Pterygotus anglicus are comparable to that of modern predatory arthropods. All species of Jaekelopterus and Pterygotus have robust crushing chelicerae, morphologically distinct from the weaker slicing chelicerae of Acutiramus. Vision in Erettopterus osiliensis and Slimonia acuminata is more acute than in Acutiramus cummingsi, but not to the same degree as in modern active predators, and the morphology of the chelicerae in these genera suggests a grasping function. The pterygotids evolved with a shift in ecology from generalized feeder to specialized predator. Pterygotid eurypterids share a characteristic morphology but, although some were top predators, their ecology differs radically between genera.
© 2015 The Author(s).
... Largely similar mean values of Procrustes variance of the two bones further indicate that both elements reflect similar degrees of intraspecific and intrageneric variability. It has previously been shown that character-and geometric morphometric-based approaches produce comparable measures of disparity (Hetherington et al. 2015) and e.g., in pterosaurs, similar degrees of disparity were captured when considering only the skull, the whole skeleton, or certain limb proportions (Foth et al. 2012). Our results complement these analyses and suggest that similar degrees of intraspecific variability can be detected also when considering different isolated skull bones. ...
Comparisons of extant and extinct biodiversity are often dependent on objective morphology-based identifications of fossils and assume a well-established and comparable taxonomy for both fossil and modern taxa. However, since many modern (cryptic) species are delimitated mainly via external morphology and / or molecular data, it is often unclear to what degree fossilized (osteological) remains allow classification to a similar level. When intraspecific morphological variation in extant taxa is poorly known, the definition of extinct species as well as the referral of fossils to extant species can be heavily biased, particularly if fossils are represented by incomplete isolated skeletal elements. This problem is especially pronounced in squamates (lizards and snakes) owing to a lack of osteological comparative knowledge for many lower taxonomic groups, concomitant with a recent increase of molecular studies revealing great cryptic diversity. Here, we apply a quantitative approach using 3D geometric morphometrics on 238 individuals of 14 genera of extant Australian and Papua New Guinean agamid lizards to test the value of two isolated skull bones (frontals and maxillae) for inferring taxonomic and ecological affinities. We further test for the consistency of intra- and interspecific morphological variability of these elements as a proxy for extinct taxonomic richness. We show that both bones are diagnostic at the generic level, and both can infer microhabitat and are of palaeoecological utility. However, species-level diversity is likely underestimated by both elements, with ~30-40% of species pairs showing no significant differences in shape. Mean intraspecific morphological variability is largely consistent across species and bones and thus a useful proxy for extinct species diversity. Reducing sample size and landmark completeness to approximate fossil specimens led to decreased classification accuracy and increased variance of morphological disparity, raising further doubts on the transferability of modern species borders to the fossil record of agamids. Our results highlight the need to establish appropriate levels of morphology-based taxonomic or ecological groupings prior to comparing extant and extinct biodiversity.
... However, nonarchosaurian archosauromorphs and pterosaurs were found to differ significantly from other major groups in their correlation. This is not surprising considering the evolution of unusually large skull sizes in groups such as erythrosuchids (Bestwick et al., 2022) and the diversity of skull morphologies in pterosaurs (Foth et al., 2012). Within dinosaurs, the level of correlation is even stronger among individual groups. ...
... However, two facts make this unlikely: first, several studies have found congruence between traditional morphometric data and discrete characters, suggesting that they capture common patterns (e.g. Foth et al. 2012, Hetherington et al. 2015, Schaeffer et al. 2020. Second, the high support observed for the OU model in Table 3. Relative support (corrected Akaike Information Criterion values) for evolutionary models (Brownian Motion (BM); Orstein-Uhlenbeck (OU); directional; κ; δ) fit to acoustic, visual and behavioural traits in manakins. ...
Sexual traits such as visual adornments, sound-based cues, and courtship dances are frequently displayed in combination as multimodal signals. Some hypotheses propose that different signals trade-off with each other potentially due to resource limitations (‘trade-off’ or transfer hypothesis) or that these develop simultaneously to enhance communication effectiveness (‘joint evolution’ hypothesis). Alternatively, multiple cues may evolve independently to serve distinct functions or convey different information (‘multiple messages’ hypothesis). Here, we explored the interdependence between different signal modalities in manakins (Pipridae), which are known for great interspecific diversity in the degree of elaboration in courtship dance, song, and plumage coloration. We also used comparative methods to explore the mode of evolution and the degree of conservatism of these signals. We found that song, plumage coloration, and courtship dance evolved independently since there was no correlation between these traits. Song evolution in manakins was attracted to a single optimum and exhibited a weak phylogenetic signal in comparison with those of color and behavioral diversity. The high support found for the speciational model when analyzing the multivariate estimates of trait variability suggests that these signals (especially color and behavior attributes) may have evolved in a punctuated manner, with large evolutionary changes at speciation events and minimal subsequent changes along the branches. Our results show that song, color, and dance diversity are each related to different ecological factors, indicating that sexual signals in manakins convey different information and/or respond to different selection pressures. Larger species and those with lower dispersal capacity tend to exhibit higher color richness, which in turn differed among lek categories, being higher in species with “classic” leks and lower in non-lekking species. Overall, the present study supports the idea that correlation between signal modalities does not constitute a widespread pattern in songbirds.
... Where disparity derived from both morphometric and discrete data have been compared, patterns are surprisingly congruent (Guillerme, Cooper, et al., 2020). However, such comparisons are necessarily at lower taxonomic levels, such as within pterosaurs (Foth et al., 2012), caecilians (Hetherington et al., 2015), captorhinids (Romano et al., 2017), osteostracans (Ferrón et al., 2020), or across more conservative structures such as theropod jaws (Schaeffer et al., 2020). The most telling comparisons-across higher taxa and the most disparate bodyplans-cannot be made almost by definition. ...
Indices of morphological disparity seek to summarise the highly multivariate morphological variation across groups of species within clades, time bins or other groups. Morphological variation can be quantified using geometric morphometric, outline or surface-based methods. These are most effective when morphological differences are relatively modest and there are numerous ubiquitous landmarks and phase aligned features of shape variation. The most disparate samples, such as those across classes and phyla, typically necessitate the use of discrete characters. Unfortunately, such characters are often compiled subjectively in a manner reflecting the level of morphological and taxonomic focus and the intensity of taxon sampling.
Sampling intensity is often highly variable within a single data set, especially in repurposed and amalgamated cladistic matrices. Here, we propose indices of molecular disparity analogous to those of morphological disparity. Despite numerous shortcomings discussed here, molecular sequence data can be obtained in a more objective, automated and scalable manner than morphological data.
Comparisons of the morphological and molecular disparity of subclades in 16 large data sets suggest that molecular disparity is less susceptible to sampling biases than morphological disparity. Moreover, distance matrices inferred from individual genes tend to correlate strongly with each other and with distances from all concatenated genes. By contrast, morphological and molecular disparity are typically not significantly correlated across subclades, such that comparisons for groups can help to give a fuller picture of their evolution. For example, within mammals, Afrotheria have conspicuously high morphological disparity but modest molecular disparity, suggesting unusually high morphological plasticity. Even more strikingly, the molecular disparity of rodents is over five times that for Artiodactyla, despite having only half of their morphological disparity. These contrasts suggest the differential operation of geometric, biomechanical, ontogenetic and environmental constraints on form.
Given the increasing abundance of total evidence datasets in the literature and the widespread and sometimes uncritical repurposing of discrete morphological matrices, we propose the comparison of morphological and molecular disparity as a useful tool to understand subclade evolution more fully.
... Recent instrumental advances in geometric morphometric techniques have supported an extensive body of research considering the comparative morphology, functioning, and development of the skull (Stayton, 2005;Pierce et al., 2009;Brusatte et al., 2011;Foth et al., 2012;Esteve-Altava et al., 2013;Fabre et al., 2014;Lu et al., 2014;Parr et al., 2016;McCurry et al., 2017;Felice and Goswami, 2018;Heck et al., 2018;Bardua et al., 2019;Evans et al., 2019). In contrast, relatively little work focusses on the comparative morphology of cranial sutures (Kathe, 1999;Monteiro and Lessa, 2000;Byron, 2009;Buezas et al., 2017). ...
Phenotypic variation across mammals is extensive and reflects their ecological diversification into a remarkable range of habitats on every continent and in every ocean. The skull performs many functions to enable each species to thrive within its unique ecological niche, from prey acquisition, feeding, sensory capture (supporting vision and hearing) to brain protection. Diversity of skull function is reflected by its complex and highly variable morphology. Cranial morphology can be quantified using geometric morphometric techniques to offer invaluable insights into evolutionary patterns, ecomorphology, development, taxonomy, and phylogenetics. Therefore, the skull is one of the best suited skeletal elements for developmental and evolutionary analyses. In contrast, less attention is dedicated to the fibrous sutural joints separating the cranial bones. Throughout postnatal craniofacial development, sutures function as sites of bone growth, accommodating expansion of a growing brain. As growth frontiers, cranial sutures are actively responsible for the size and shape of the cranial bones, with overall skull shape being altered by changes to both the level and time period of activity of a given cranial suture. In keeping with this, pathological premature closure of sutures postnatally causes profound misshaping of the skull (craniosynostosis). Beyond this crucial role, sutures also function postnatally to provide locomotive shock absorption, allow joint mobility during feeding, and, in later postnatal stages, suture fusion acts to protect the developed brain. All these sutural functions have a clear impact on overall cranial function, development and morphology, and highlight the importance that patterns of suture development have in shaping the diversity of cranial morphology across taxa. Here we focus on the mammalian cranial system and review the intrinsic relationship between suture development and morphology and cranial shape from an evolutionary developmental biology perspective, with a view to understanding the influence of sutures on evolutionary diversity. Future work integrating suture development into a comparative evolutionary framework will be instrumental to understanding how developmental mechanisms shaping sutures ultimately influence evolutionary diversity.
... These techniques have grown a particular interest and have been successful in the study of vertebrate morphology during the past three decades. Within the system of the vertebrate skull, the overwhelming focus of morphometric studies has been the bony structures themselves, with little attention given to the sutural joints between these cranial bones [11][12][13][14][15][16][17][18][19][20][21][22]. ...
Cranial sutures play critical roles in facilitating postnatal skull development and function. The diversity of function is reflected in the highly variable suture morphology and complexity. Suture complexity has seldom been studied, resulting in little consensus on the most appropriate approach for comparative, quantitative analyses. Here, we provide the first comprehensive comparison of current approaches for quantifying suture morphology, using a wide range of two-dimensional suture outlines across extinct and extant mammals (n = 79). Five complexity metrics (sinuosity index (SI), suture complexity index (SCI), fractal dimension (FD) box counting, FD madogram and a windowed short-time Fourier transform with power spectrum density (PSD) calculation) were compared with each other and with the shape variation in the dataset. Analyses of suture shape demonstrate that the primary axis of variation captured attributes other than complexity, supporting the use of a complexity metric over raw shape data for sutural complexity analyses. Each approach captured different aspects of complexity. PSD successfully discriminates different sutural features, such as looping patterns and interdigitation amplitude and number, while SCI best-captured variation in interdigitation number alone. Therefore, future studies should consider the relevant attributes for their question when selecting a metric for comparative analysis of suture variation, function and evolution.
... This result is surprising given that most paleobiological evidence for early burst-like dynamics comes from analyses of multivariate character data that characterize overall organismal form (Westoll, 1949;Foote, 1995;Hughes et al., 2013). Although several authors have shown that cladistic and morphometric data can provide similar characterizations of clade disparity (Villier and Eble, 2004;Anderson and Friedman, 2012;Foth et al., 2012;Hetherington et al., 2015) few have examined whether the 26 . CC-BY-NC-ND 4.0 International license a certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. ...
A bstract
Henry Fairfield Osborn’s law of adaptive radiation was intended to explain the early proliferation of morphological and functional variation in diversifying clades. Yet, despite much theoretical development and empirical testing, questions remain regarding the taxonomic levels at which adaptive radiation occurs, the traits involved, and its frequency across the tree of life. Here, we evaluate support for this “early burst” model of adaptive radiation in 14 ecomorphological traits plus body mass for the extant mammalian order Carnivora. Strong support for an early burst adaptive radiation is recovered for molar grinding area, a key proxy for diet. However, we find no evidence for early burst–like dynamics in body mass or multivariate trait data, suggesting a decoupling of evolutionary modes among traits driven by dietary specialization. Furthermore, the signal of an early burst is only recovered for Carnivora, and not in family–level clades. The lack of support for the early burst model of morphological adaptive radiation in previous phylogenetic studies may be a consequence of focusing on the wrong traits at the wrong taxonomic levels. Osborn’s law predicted that adaptive radiation should be hierarchically structured, and the search for its signature and understanding of its prevalence will require a renewed focus on functional traits and their evolution over higher-level clades.
... Pterosaurs are an extinct clade of flying Mesozoic reptiles, with a 150-million-year fossil record from the Late Triassic to the latest Cretaceous (Wellnhofer, 1991;Chatterjee & Templin, 2004;Unwin, 2006;Butler, Benson & Barrett, 2013). The current number of described pterosaur species is around 190, and the clade exhibits wide morphological disparity ( Fig. 1) (Prentice, Ruta & Benton, 2011;Butler et al., 2012;Foth, Brusatte & Butler, 2012;Hyder, Witton & Martill, 2014), with wingspans ranging from 40 cm to 10 m (Hone & Benton, 2008;Benson et al., 2014). Pterosaur Biological Reviews (2018) research has advanced rapidly during the last three decades (Barrett et al., 2008;Hone, 2012;Witton, 2013), with new finds of fossil Lagerstätten in Brazil and China yielding numerous well-preserved pterosaur specimens. ...
Pterosaurs are an extinct group of Mesozoic flying reptiles, whose fossil record extends from approximately 210 to 66 million years ago. They were integral components of continental and marginal marine ecosystems, yet their diets remain poorly constrained. Numerous dietary hypotheses have been proposed for different pterosaur groups, including insectivory, piscivory, carnivory, durophagy, herbivory/frugivory, filter‐feeding and generalism. These hypotheses, and subsequent interpretations of pterosaur diet, are supported by qualitative (content fossils, associations, ichnology, comparative anatomy) and/or quantitative (functional morphology, stable isotope analysis) evidence. Pterosaur dietary interpretations are scattered throughout the literature with little attention paid to the supporting evidence. Reaching a robustly supported consensus on pterosaur diets is important for understanding their dietary evolution, and their roles in Mesozoic ecosystems. A comprehensive examination of the pterosaur literature identified 314 dietary interpretations (dietary statement plus supporting evidence) from 126 published studies. Multiple alternative diets have been hypothesised for most principal taxonomic pterosaur groups. Some groups exhibit a high degree of consensus, supported by multiple lines of evidence, while others exhibit less consensus. Qualitative evidence supports 87.3% of dietary interpretations, with comparative anatomy most common (62.1% of total). More speciose groups of pterosaur tend to have a greater range of hypothesised diets. Consideration of dietary interpretations within alternative phylogenetic contexts reveals high levels of consensus between equivalent monofenestratan groups, and lower levels of consensus between equivalent non‐monofenestratan groups. Evaluating the possible non‐biological controls on apparent patterns of dietary diversity reveals that numbers of dietary interpretations through time exhibit no correlation with patterns of publication (number of peer‐reviewed publications through time). 73.8% of dietary interpretations were published in the 21st century. Overall, consensus interpretations of pterosaur diets are better accounted for by non‐biological signals, such as the impact of the respective quality of the fossil record of different pterosaur groups on research levels. That many interpretations are based on qualitative, often untestable lines of evidence adds significant noise to the data. More experiment‐led pterosaur dietary research, with greater consideration of pterosaurs as organisms with independent evolutionary histories, will lead to more robust conclusions drawn from repeatable results. This will allow greater understanding of pterosaur dietary diversity, disparity and evolution and facilitate reconstructions of Mesozoic ecosystems.
... To reconstruct the disparity of Cornales through time, the original data matrix was modified to only include taxa with drupaceous fruits because reported cornalean fossils of other fruit types are rare (e.g., capsules, but see Manchester, 1994). Disparity analyses commonly use single structures or organs as proxies for the whole organism (see Foth et al., 2012). Similarly, in this study, fruits are cautiously used as a proxy for the entire plant. ...
PREMISE OF THE STUDY: The basal asterid order, Cornales, experienced a rapid radiation during the Cretaceous, which has made it dicult to elucidate the early evolution of the order using extant taxa only. Recent paleobotanical studies, however, have begun to shed light on the early diversication of Cornales. Herein, fossils are directly incorporated in phylogenetic and quantitative morphological analyses to reconstruct early cornalean evolution.
METHODS: A morphological matrix of 77 fruit characters and 58 taxa (24 extinct) was assembled. Parsimony analyses including and excluding fossils were conducted. A fossil inclusive tree was time- scaled to visualize the timing of the initial cornalean radiation. Disparity analyses were utilized to infer the morphological evolution of cornaleans with drupaceous fruits.
KEY RESULTS: Fossil inclusive and exclusive parsimony analyses resulted in well- resolved deep- node relationships within Cornales. Resolution in the fossil inclusive analysis is substantially higher, revealing a basal grade including Loasaceae, Hydrangeaceae, Hydrostachyaceae, Grubbiaceae, a Hironoia+Amersinia clade, and Curtisiaceae, respectively, that leads to a “core” group containing a clade comprising a Cretaceous grade leading to clade of Nyssaceae, Mastixiaceae, and Davidiaceae that is sister to a Cornaceae+Alangiaceae clade. The time- scaled tree indicates that the initial cornalean diversication occurred before 89.8 Ma. Disparity analyses suggest the morphological diversity of Cornales peaked during the Paleogene.
CONCLUSIONS: Phylogenetic analyses clearly demonstrate that novel character mosaics of Cretaceous cornaleans play a critical role in resolving deep- node relationships within Cornales. The post- Cretaceous increase of cornalean disparity is associated with a shift in morphospace occupation, which can be explained from ecological and developmental perspectives.
... The slowdown phenomenon has been widely reported and is often considered pervasive in nature (but see ref. 23 ), with famous examples ranging from cichlid fishes 24 to Anolis lizards 25 , Darwin's finches 26 (although these examples are geographically restricted) and, more recently, dinosaurs 3 -yet the causes underpinning this type of radiation pattern remain unclear. Osborn 27,28 , who first coined the term adaptive radiation, suggested that species emerge in response to adaptive or 'mechanical' changes associated with ecological opportunity (the number of open or underused niches within an environment). speeds (bottom) for each of the three periods of the Mesozoic era (green, Triassic; red, Jurassic; purple, Cretaceous). ...
Dinosaurs dominated terrestrial ecosystems across the globe for over 100 million years and provide a classic example of an evolutionary radiation. However, little is known about how these animals radiated geographically to become globally distributed. Here, we use a biogeographical model to reconstruct the dinosaurs' ancestral locations, revealing the spatial mechanisms that underpinned this 170-million-year-long radiation. We find that dinosaurs spread rapidly initially, followed by a significant continuous and gradual reduction in their speed of movement towards the Cretaceous/Tertiary boundary (66 million years ago). This suggests that the predominant mode of dinosaur speciation changed through time with speciation originally largely driven by geographical isolation-when dinosaurs speciated more, they moved further. This was gradually replaced by increasing levels of sympatric speciation (species taking advantage of ecological opportunities within their existing environment) as terrestrial space became a limiting factor. Our results uncover the geographical signature of an evolutionary radiation.
... Pterosaurs are an extinct clade of flying Mesozoic reptiles, with a 150-million-year fossil record from the Late Triassic to the latest Cretaceous (Wellnhofer, 1991;Chatterjee & Templin, 2004;Unwin, 2006;Butler, Benson & Barrett, 2013). The current number of described pterosaur species is around 190, and the clade exhibits wide morphological disparity ( Fig. 1) (Prentice, Ruta & Benton, 2011;Butler et al., 2012;Foth, Brusatte & Butler, 2012;Hyder, Witton & Martill, 2014), with wingspans ranging from 40 cm to 10 m (Hone & Benton, 2008;Benson et al., 2014). Pterosaur Biological Reviews (2018) research has advanced rapidly during the last three decades (Barrett et al., 2008;Hone, 2012;Witton, 2013), with new finds of fossil Lagerstätten in Brazil and China yielding numerous well-preserved pterosaur specimens. ...
Pterosaurs were a successful group of Mesozoic flying reptiles. For 150 million years they were integral components of terrestrial and coastal ecosystems, yet their feeding ecology remains poorly constrained. Postulated pterosaur diets include insectivory, piscivory and/or carnivory, but many dietary hypotheses are little more than speculation based on scant evidence. We have developed a more robust approach based on quantitative analysis of the micron-scale 3D textures of worn pterosaur tooth surfaces – dental microwear texture analysis – never before applied to pterosaurs. Microwear is produced as scratches and chips generated by food items create characteristic surface textures on teeth that vary according to diet.
We compared microwear from non-occlusal tooth surfaces of 11 species of pterosaur with data from extant organisms with known diets, (bats, monitor lizards and crocodilians, including insectivorous, piscivorous and carnivorous species). This allowed for robust testing of previous pterosaur dietary hypotheses. Microwear from Dimorphodon for example, previously hypothesised as a piscivore, indicates a diet of vertebrates and invertebrates. Microwear from basal monofenestratans, previously hypothesised as carnivores, provides evidence of piscivory in these pterosaurs. Dietary evidence from microwear therefore provides novel insights into the ecological roles of respective pterosaurs and pterosaur dietary evolution.
... Over the course of the last decades, the combination of geometric morphometrics with phylogenetic comparative methods has become a promising resource for the study of macroevolutionary dynamics, including the evolution of disparity, which quantifies morphological diversity as opposed to taxonomic, functional or phylogenetic diversity [1][2][3][4][5]. In comparison with studies of taxonomic diversity, however, studies of morphological disparity have only recently begun to make fuller use of a phylogenetic framework by including information from ghost lineages. ...
In a previous study, we estimated the cranial disparity of turtles (Testudinata) through time using geometric morphometric data from both terminal taxa and hypothetical ancestors to compensate for temporal gaps in the fossil record. While this method yielded reasonable results for the Mesozoic and the early Cenozoic, we found a large drop in cranial disparity for the Miocene, for which we found no correlation with known environmental changes or extinction events. Instead,we speculated that the Miocene dip was a result of poor sampling of fossils or ancestors in this time bin. To countervail this problem, we here updated our original dataset and interpolated changes of shape along the branch lengths and compared them with the previous data. We furthermore explored the impact of topological and temporal uncertainty, demonstrating that the Miocene dip, indeed, is a sampling artefact. All remaining conclusions of the previous study could be more or less supported, nevertheless, including an apparent correlation with global biogeographic events, a minor correlation between cranial disparity and global temperature, and resilience across the K/T extinction event.
... However, the geologically oldest pterosaurs are from Late Triassic (Norian) marine deposits of the Alps and Greenland [5]. During their 149 million year history, from the Late Triassic (215 Ma) to the end of the Cretaceous (66 Ma), the evolution of pterosaurs resulted in a variety of ecomorphological adaptations, as evidenced by differences in skull shape, dentition, body size and body plan (neck length, tail length and wing span) [2][3][4]9,10]. The most striking differentiation of their feeding adaptations correlated with morphological and phylogenetic diversity took place concurrently with the rise of the Pterodactyloidea, the most species-diverse group of pterosaurs that ruled the sky from Late Jurassic to the end of Cretaceous. The new discovery from China reported here documents the only pre-Tithonian pterodactyloid known with a complete skull, shedding new light on the origin of the Ctenochasmatidae and the timing of the critical transition from fish-catching to filter-feeding, a major ecological shift in the early history of the pterodactyloid clade. ...
Pterosaurs were a unique clade of flying reptiles that were contemporaries of dinosaurs in Mesozoic ecosystems. The Pterodactyloidea as the most species-diverse group of pterosaurs dominated the sky during Cretaceous time, but earlier phases of their evolution remain poorly known. Here, we describe a 160Ma filter-feeding pterosaur from western Liaoning, China, representing the geologically oldest record of the Ctenochasmatidae, a group of exclusive filter feeders characterized by an elongated snout and numerous fine teeth. The new pterosaur took the lead of a major ecological transition in pterosaur evolution from fish-catching to filter-feeding adaptation, prior to the Tithonian (145–152 Ma) diversification of the Ctenochasmatidae. Our research shows that the rise of ctenochasmatid pterosaurs was followed by the burst of eco-morphological divergence of other pterodactyloid clades, which involved a wide range of feeding adaptations that considerably altered the terrestrial ecosystems of the Cretaceous world.
... However, the geologically oldest pterosaurs are from Late Triassic (Norian) marine deposits of the Alps and Greenland [5]. During their 149 million year history, from the Late Triassic (215 Ma) to the end of the Cretaceous (66 Ma), the evolution of pterosaurs resulted in a variety of ecomorphological adaptations, as evidenced by differences in skull shape, dentition, body size and body plan (neck length, tail length and wing span) [2][3][4]9,10]. The most striking differentiation of their feeding adaptations correlated with morphological and phylogenetic diversity took place concurrently with the rise of the Pterodactyloidea, the most species-diverse group of pterosaurs that ruled the sky from Late Jurassic to the end of Cretaceous. The new discovery from China reported here documents the only pre-Tithonian pterodactyloid known with a complete skull, shedding new light on the origin of the Ctenochasmatidae and the timing of the critical transition from fish-catching to filter-feeding, a major ecological shift in the early history of the pterodactyloid clade. ...
Pterosaurs were a unique clade of flying reptiles that were contemporaries of dinosaurs in Mesozoic ecosystems. The Pterodactyloidea as the most species-diverse group of pterosaurs dominated the sky during Cretaceous time, but earlier phases of their evolution remain poorly known. Here, we describe a 160 Ma filter-feeding pterosaur from western Liaoning, China, representing the geologically oldest record of the Ctenochasmatidae, a group of exclusive filter feeders characterized by an elongated snout and numerous fine teeth. The new pterosaur took the lead of a major ecological transition in pterosaur evolution from fish-catching to filter-feeding adaptation, prior to the Tithonian (145–152 Ma) diversification of the Ctenochasmatidae. Our research shows that the rise of ctenochasmatid pterosaurs was followed by the burst of eco-morphological divergence of other pterodactyloid clades, which involved a wide range of feeding adaptations that considerably altered the terrestrial ecosystems of the Cretaceous world.
... Among morphological studies in the vertebrate literature, both those using geometric morphometrics (GMM) and studies using linear or cross-sectional measurements, there is a clear bias towards the morphology of the skull (e.g. Meachen-Samuels and Van Valkenburgh 2009a;Slater and Van Valkenburgh 2008;Fabre et al. 2014;Stayton 2005;Figueirido et al. 2010;Goswami and Polly 2010;Goswami 2006;Pierce et al. 2008Pierce et al. , 2009Piras et al. 2013;Drake and Klingenberg 2010;Foth et al. 2012;Meachen et al. 2014), followed by studies of the limbs (e.g. Bennett and Goswami 2011;Fabre et al. 2013;Bell et al. 2011;Alvarez et al. 2013;Martin-Serra et al. 2014;Adams and Nistri 2010;Walmsley et al. 2012;Zhang et al. 2012;Andersson and Werdelin 2003;Ercoli et al. 2012;Sears et al. 2013;Meachen-Samuels and Van Valkenburgh 2009b;Doube et al. 2009). ...
Recent advances in geometric morphometrics provide improved techniques for extraction of biological information from shape and have greatly contributed to the study of ecomorphology and morphological evolution. However, the vertebral column remains an under-studied structure due in part to a concentration on skull and limb research, but most importantly because of the difficulties in analysing the shape of a structure composed of multiple articulating discrete units (i.e. vertebrae). Here, we have applied a variety of geometric morphometric analyses to three-dimensional landmarks collected on 19 presacral vertebrae to investigate the influence of potential ecological and functional drivers, such as size, locomotion and prey size specialisation, on regional morphology of the vertebral column in the mammalian family Felidae. In particular, we have here provided a novel application of a method—phenotypic trajectory analysis (PTA)—that allows for shape analysis of a contiguous sequence of vertebrae as functionally linked osteological structures. Our results showed that ecological factors influence the shape of the vertebral column heterogeneously and that distinct vertebral sections may be under different selection pressures. While anterior presacral vertebrae may either have evolved under stronger phylogenetic constraints or are ecologically conservative, posterior presacral vertebrae, specifically in the post-T10 region, show significant differentiation among ecomorphs. Additionally, our PTA results demonstrated that functional vertebral regions differ among felid ecomorphs mainly in the relative covariation of vertebral shape variables (i.e. direction of trajectories, rather than in trajectory size) and, therefore, that ecological divergence among felid species is reflected by morphological changes in vertebral column shape.
... Data are handled during this process in a phenetic manner, with no assumptions of hierarchy or homoplasy, and as such it is not circular to compare results from disparity analyses to the phylogenetic hierarchy retrieved from the same character matrix. Analyses of disparity formulated from discrete character matrices have been shown to converge on a common signal with other forms of morphometric data (Foth et al. 2012;Hetherington et al. 2015) and so results are comparable with those attained from, for example, landmark data. ...
Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the 'Big Five' mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems.
... Several previous studies have found converging signals when different disparity proxies were applied [50][51][52], while the current study reveals partial differences between disparity analyses using discrete characters [22,48] and those based on geometric morphometric data. These discrepancies could be due to a variety of reasons, including differences in taxonomic sampling, weaknesses of either the discrete character or morphometric datasets, or discrepancies between cranial and postcranial disparity in highly specialized clades such as pterosaurs. ...
Background:
Archosauromorpha originated in the middle-late Permian, radiated during the Triassic, and gave rise to the crown group Archosauria, a highly successful clade of reptiles in terrestrial ecosystems over the last 250 million years. However, scientific attention has mainly focused on the diversification of archosaurs, while their stem lineage (i.e. non-archosaurian archosauromorphs) has often been overlooked in discussions of the evolutionary success of Archosauria. Here, we analyse the cranial disparity of late Permian to Early Jurassic archosauromorphs and make comparisons between non-archosaurian archosauromorphs and archosaurs (including Pseudosuchia and Ornithodira) on the basis of two-dimensional geometric morphometrics.
Results:
Our analysis recovers previously unappreciated high morphological disparity for non-archosaurian archosauromorphs, especially during the Middle Triassic, which abruptly declined during the early Late Triassic (Carnian). By contrast, cranial disparity of archosaurs increased from the Middle Triassic into the Late Triassic, declined during the end-Triassic extinction, but re-expanded towards the end of the Early Jurassic.
Conclusions:
Our study indicates that non-archosaurian archosauromorphs were highly diverse components of terrestrial ecosystems prior to the major radiation of archosaurs, including dinosaurs, while disparity patterns of the Ladinian and Carnian indicate a gradual faunal replacement of stem archosaurs by the crown group, including a short interval of partial overlap in morphospace during the Ladinian.
... Pragmatically, we might ask whether these biases really matter. One way that this can be achieved is by comparing disparity inferred from discrete characters with that from other morphometric approaches (Anderson & Friedman, 2012;Foth, Brusatte & Butler, 2012;Hetherington et al., 2015), which, in theory, lack these biases. So far, such studies show good congruence between the two techniques, at least for the groups concerned, suggesting that we appear to be capturing the same signal. ...
Discrete character-taxon matrices are increasingly being used in an attempt to understand the pattern and tempo of morphological evolution; however, methodological sophistication and bespoke software implementations have lagged behind. In the present study, an attempt is made to provide a state-of-the-art description of methodologies and introduce a new R package (Claddis) for performing foundational disparity (morphologic diversity) and rate calculations. Simulations using its core functions show that: (1) of the two most commonly used distance metrics (Generalized Euclidean Distance and Gower's Coefficient), the latter tends to carry forward more of the true signal; (2) a novel distance metric may improve signal retention further; (3) this signal retention may come at the cost of pruning incomplete taxa from the data set; and (4) the utility of bivariate plots of ordination spaces are undermined by their frequently extremely low variances. By contrast, challenges to estimating morphologic tempo are presented qualitatively, such as how trees are time-scaled and changes are counted. Both disparity and rates deserve better time series approaches that could unlock new macroevolutionary analyses. However, these challenges need not be fatal, and several potential future solutions and directions are suggested.
... These methodological discrepancies hamper morphometric analyses based on illustrations appearing in the previously published literature. This situation contrasts with fossil organisms, such as dinosaurs, in which many morphological descriptions have been produced using the same (or, at least, comparable) procedure among different studies and, thus, illustrations obtained from the published literature (photographs/reconstructions) are frequently used in subsequent geometric morphometric studies Foth, Brusatte & Butler, 2012;Maiorino et al., 2013). For carabid larvae, the use of the same methodological procedures in morphological descriptions would facilitate future morphometric studies based on the published literature. ...
Feeding habits are important life-history traits in animals; however, methods for their determination are not well established in many species. The larvae of the beetle family Carabidae are an example. The present study tested the utility of geometric morphometrics of mouthpart morphology to infer the feeding habits of carabid larvae. Using Pterostichus thunbergi as a model system, larval feeding habits were inferred using geometric morphometrics of mouthparts and the results were compared with those obtained from rearing experiments. The rearing experiments indicated that P. thunbergi larvae are carnivores that require snails as an essential part of the diet. Through geometric morphometrics, associations between mouthpart morphology and larval feeding habits were confirmed for species in which these two traits are known. A discriminant analysis using these associations classified P. thunbergi larvae as snail/slug feeders, which is a result compatible with the rearing experiments. Geometric morphometrics also revealed that morphological integration and ontogenetic shape change might play roles in the diversification of mouthpart morphology. Overall, these results demonstrate the utility of the geometric morphometrics of mouthparts to infer feeding habit and to clarify the mechanisms of mouthpart morphological diversification in the study group, and the results also serve as a basis for future studies of other insect groups.
... While such character matrices are typically developed to infer phylogenetic relationships, rather than morphological disparity per se, studies have shown that they give results similar to other methods for measuring disparity (e.g. morphometric data [14,15]). This suggests that, in principle, such matrices are suitable for use in macroevolutionary studies. ...
There is increasing evidence that early mammals evolved rapidly into a range of body forms and habitats, right under the noses of the dinosaurs.
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... This is in contrast to Rajoidei, which appear to have been displaced to depths up to 3000 m (Compagno, 1999;Siverson and Cappetta, 2001;Frisk, 2010) and have the lowest dis-parity, perhaps due to a less dynamic environment at depth. While the disparity measures are focused on pectoral morphology, Foth et al. (2012) proved such focused measures can be accurate of actual disparity. ...
The diverse cartilaginous fish lineage, Batoidea (rays, skates, and allies), sister taxon to sharks, comprises a huge range of morphological diversity which to date remains unquantified and unexplained in terms of evolution or locomotor style. A recent molecular phylogeny has enabled us to confidently assess broadscale aspects of morphology across Batoidea. Geometric morphometrics quantifies the major aspects of shape variation, focusing on the enlarged pectoral fins which characterize batoids, to explore relationships between ancestry, locomotion and habitat. A database of 253 specimens, encompassing 60 of the 72 batoid genera, reveals that the majority of morphological variation across Batoidea is attributable to fin aspect-ratio and the chordwise location of fin apexes. Both aspect-ratio and apex location exhibit significant phylogenetic signal. Standardized independent linear contrast analysis reveals that fin aspect-ratio can predict locomotor style. This study provides the first evidence that low aspect-ratio fins are correlated with undulatory-style locomotion in batoids, whereas high aspect-ratio fins are correlated with oscillatory locomotion. We also show that it is phylogeny that determines locomotor style. In addition, body- and caudal fin-locomotors are shown to exhibit low aspect-ratio fins, whereas a pelagic lifestyle correlates with high aspect-ratio fins. These results emphasize the importance of phylogeny in determining batoid pectoral fin shape, however, interactions with other constraints, most notably locomotor style, are also highlighted as significant. J. Morphol., 2014. © 2014 Wiley Periodicals, Inc.
Pterosaurs, the earliest flying tetrapods, are the subject of some recent quantitative macroevolutionary analyses from different perspectives. Here, we use an integrative approach involving newly assembled phylogenetic and body size datasets, net diversification rates, morphological rates, and morphological disparity to gain a holistic understanding of the pterosaur macroevolution. The first two parameters are important in quantitative analyses of macroevolution, but they have been rarely used in previous pterosaur studies. Our study reveals an ∼115-Ma period—from Early Triassic to Early Cretaceous—of multi-wave increasing net diversification rates and disparity, as well as high morphological rates, followed by an ∼65-Ma period—from Early Cretaceous to the end of the Cretaceous—of mostly negative net diversification rates, decreasing disparity, and relatively low morphological rates in pterosaur evolution. Our study demonstrates the following: (1) body size plays an important role in pterosaur lineage diversification during nearly their whole evolutionary history, and the evolution of locomotion, trophic, and ornamental structures also plays a role in different periods; (2) birds, the other major flying tetrapod group at the time, might have affected pterosaur macroevolution for ∼100 Ma; and (3) different mass extinction events might have affected pterosaur evolution differently. Particularly, the revealed decline in pterosaur biodiversity during the Middle and Late Cretaceous periods provides further support for the possible presence of a biodiversity decline of large-sized terrestrial amniotes starting in the mid-Cretaceous, which may have been caused by multiple factors including a global land area decrease during these periods.
Principal coordinates analysis (PCoA) is a statistical ordination technique commonly applied to morphology-based cladistic matrices to study macroevolutionary patterns, morphospace occupation, and disparity. However, PCoA-based morphospaces are dissociated from the original data; therefore, whether such morphospaces accurately reflect body-plan disparity or extrinsic factors, such as body size, remains uncertain. We collated nine character–taxon matrices of dinosaurs together with body-mass estimates for all taxa and tested for relationships between body size and both the principal axis of variation (i.e., PCo1) and the entire set of PCo scores. The possible effects of body size on macroevolutionary hypotheses derived from ordinated matrices were tested by reevaluating evidence for the accelerated accumulation of avian-type traits indicated by a strong directional shift in PCo1 scores in hypothetical ancestors of modern birds. Body mass significantly accounted for, on average, approximately 50% and 16% of the phylogenetically corrected variance in PCo1 and all PCo scores, respectively. Along the avian stem lineage, approximately 30% of the morphological variation is attributed to the reconstructed body masses of each ancestor. When the effects of body size are adjusted, the period of accelerated trait accumulation is replaced by a more gradual, additive process. Our results indicate that even at low proportions of variance, body size can noticeably affect macroevolutionary hypotheses generated from ordinated morphospaces. Future studies should thoroughly explore the nature of their character data in association with PCoA-based morphospaces and use a residual/covariate approach to account for potential correlations with body size.
Morphological variation (disparity) is almost invariably characterized by two non‐mutually exclusive approaches: (1) quantitatively, through geometric morphometrics; and (2) in terms of discrete, ‘cladistic’, or categorical characters. Uncertainty over the comparability of these approaches diminishes the potential to obtain nomothetic insights into the evolution of morphological disparity and the few benchmarking studies conducted so far show contrasting results. Here, we apply both approaches to characterizing morphology in the stem‐gnathostome clade Osteostraci in order to assess congruence between these alternative methods as well as to explore the evolutionary patterns of the group in terms of temporal disparity and the influence of phylogenetic relationships and habitat on morphospace occupation. Our results suggest that both approaches yield similar results in morphospace occupation and clustering, but also some differences indicating that these metrics may capture different aspects of morphology. Phylomorphospaces reveal convergence towards a generalized ‘horseshoe’‐shaped cranial morphology and two strong trends involving major groups of osteostracans (benneviaspidids and thyestiids), which probably reflect adaptations to different lifestyles. Temporal patterns of disparity obtained from categorical and morphometric approaches appear congruent, however, disparity maxima occur at different times in the evolutionary history of the group. The results of our analyses indicate that categorical and continuous data sets may characterize different patterns of morphological disparity and that discrepancies could reflect preservational limitations of morphometric data and differences in the potential of each data type for characterizing more or less inclusive aspects of overall phenotype.
Disparity, the diversity of form and function of organisms, can be assessed from cladistic or phenetic characters , and from discrete characters or continuous characters such as landmarks, outlines, or ratios. But do these different methods of assessing disparity provide comparable results? Here we provide evidence that all metrics correlate significantly with each other and capture similar patterns of morphological variation. We compare three methods of capturing morphological disparity (discrete characters, geometric mor-phometric outlines and geometric morphometric landmarks) in coelurosaurian dinosaurs. We standardize our study by focusing all our metrics on the mandible, so avoiding the risk of confounding disparity methods with anatomical coverage of the taxa. The correlation is strongest between the two geometric morphometric methods, and weaker between the mor-phometric methods and the discrete characters. By using phylogenetic simulations of discrete character and geometric morphometric data sets, we show that the strength of these correlations is significantly greater than expected from the evolution of random data under Brownian motion. All disparity metrics confirm that Maniraptoriformes had the highest disparity of all coelurosaurians, and omnivores and herbivores had higher disparity than carnivores.
Ostracoderms (fossil armoured jawless fishes) shed light on early vertebrate evolution
by revealing the step-wise acquisition of jawed vertebrate characters, and were
important constituents of Middle Palaeozoic vertebrate faunas. A wide variety of
head shield shapes are observed within and between the ostracoderm groups, but the
timing of these diversifications and the consistency between different measures of their
morphospace are unclear. Here, we present the first disparity (explored morphospace)
versus diversity (number of taxa) analysis of Pteraspidiformes heterostracans using
continuous and discrete characters. Patterns of taxic diversity and morphological
disparity are in accordance: they both show a rise to a peak in the Lochkovian followed
by a gradual decline in the Middle-Late Devonian. Patterns are largely consistent for
disparity measures using sum of ranges or total variance, and when using continuous
or discrete characters. Pteraspidiformes heterostracans can be classified as a ``bottomheavy
clade'', i.e., a group where a high initial disparity decreasing over time is detected.
In fact, the group explored morphospace early in its evolutionary history, with much of
the subsequent variation in dermal armour occurring as variation in the proportions of
already evolved anatomical features. This Early Devonian radiation is also in agreement
with the paleobiogeographic distribution of the group, with a maximum of dispersal
and explored morphospace during the Lochkovian and Pragian time bins.
Pterosaurs, a Mesozoic group of flying archosaurs, have become a focal point for debates pertaining to the impact of sampling biases on our reading of the fossil record, as well as the utility of sampling proxies in palaeodiversity reconstructions. The completeness of the pterosaur fossil specimens themselves potentially provides additional information that is not captured in existing sampling proxies, and might shed new light on the group’s evolutionary history. Here we assess the quality of the pterosaur fossil record via a character completeness metric based on the number of phylogenetic characters that can be scored for all known skeletons of 172 valid species, with averaged completeness values calculated for each geological stage. The fossil record of pterosaurs is observed to be strongly influenced by the occurrence and distribution of Lagerstätten. Peaks in completeness correlate with Lagerstätten deposits, and a recovered correlation between completeness and observed diversity is rendered non-significant when Lagerstätten species are excluded. Intervals previously regarded as potential extinction events are shown to lack Lagerstätten and exhibit low completeness values: as such, the apparent low diversity in these intervals might be at least partly the result of poor fossil record quality. A positive correlation between temporal patterns in completeness of Cretaceous pterosaurs and birds further demonstrates the prominent role that Lagerstätten deposits have on the preservation of smaller bodied organisms, contrasting with a lack of correlation with the completeness of large-bodied sauropodomorphs. However, we unexpectedly find a strong correlation between sauropodomorph and pterosaur completeness within the Triassic–Jurassic, but not the Cretaceous, potentially relating to a shared shift in environmental preference and thus preservation style through time. This study highlights the importance of understanding the relationship between various taphonomic controls when correcting for sampling bias, and provides additional evidence for the prominent role of sampling on observed patterns in pterosaur macroevolution.
Disparity‐through‐time analyses can be used to determine how morphological diversity changes in response to mass extinctions, or to investigate the drivers of morphological change. These analyses are routinely applied to palaeobiological datasets, yet, although there is much discussion about how to best calculate disparity, there has been little consideration of how taxa should be sub‐sampled through time. Standard practice is to group taxa into discrete time bins, often based on stratigraphic periods. However, this can introduce biases when bins are of unequal size, and implicitly assumes a punctuated model of evolution. In addition, many time bins may have few or no taxa, meaning that disparity cannot be calculated for the bin and making it harder to complete downstream analyses. Here we describe a different method to complement the disparity‐through‐time tool‐kit: time‐slicing. This method uses a time‐calibrated phylogenetic tree to sample disparity‐through‐time at any fixed point in time rather than binning taxa. It uses all available data (tips, nodes and branches) to increase the power of the analyses, specifies the implied model of evolution (punctuated or gradual), and is implemented in R. We test the time‐slicing method on four example datasets and compare its performance in common disparity‐through‐time analyses. We find that the way we time sub‐sample taxa can change our interpretations of the results of disparity‐through‐time analyses. We advise using multiple methods for time sub‐sampling taxa, rather than just time binning, to gain a better understanding disparity‐through‐time.
For taphonomic and practical reasons, our understanding of morphological evolution within and among species is based primarily on measurements taken from one or a few morphological traits. However, patterns can be highly dependent on trait choice, making it difficult to draw conclusions about evolution of species or clades as a whole. In this paper, I test whether patterns of evolutionary change in the shape of a part are coincident with patterns of evolutionary change based on a more comprehensive description of the organism. The former is based on geometric morphometrics of the trilobite cranidium and the latter on discrete character data describing the exoskeleton, collected from species belonging to the Cambrian family Pterocephaliidae. Using these two datasets, I compare the amount of change occurring along phylogenetic branches, as well as changes in morphospace occupation and changes in different measures of disparity. Unlike previous studies, I apply as similar a data treatment as possible to each data set in order to facilitate the comparison and interpretation of discrepancies. Results suggest that cranidial shape is a robust proxy for species-level disparity and rates of evolution in this family of trilobites. This indicates that studies that have relied on data collected from the cranidium may be representative of the patterns that would be detected if more comprehensive description of the specimens had been available.
Turtles (Testudinata) are a diverse group of reptiles that conquered a broad set of habitats and feeding ecologies over the course of their well-documented evolutionary history. We here investigate the cranial shape of 171 representatives of the turtle lineage and the relationship of shape to different habitat and diet preferences using two-dimensional geometric morphometrics. The skull shape of extant turtles correlates with both ecological proxies, but is more affected by habitat than diet. However, the application of these correlations to extinct turtles produces mostly flawed results, as least when compared to external data such as sedimentary environment, highlighting that the morphospace held by extant turtles is not necessarily the optimal location in tree space for a particular ecology. The inability of this study to correctly predict the ecology of extinct turtles is likely related to the fact that the shape of turtle skulls is dominated by the emarginations and jaw closure mechanisms, two shape features unrelated to habitat or feeding ecology. This indicates that various specializations that are apparent in the skull only contribute little to overall shape.
Pterosaurs are an extinct group of highly modified flying reptiles that thrived during the Mesozoic. This group has unique and remarkable skeletal adaptations to powered flight, including pneumatic bones and an elongate digit IV supporting a wing-membrane. Two major body plans have traditionally been recognized: the primitive, primarily long-tailed paraphyletic “rhamphorhynchoids” (preferably currently recognized as non-pterodactyloids) and the derived short-tailed pterodactyloids. These two groups differ considerably in their general anatomy and also exhibit a remarkably different neuroanatomy and inferred head posture, which has been linked to different lifestyles and behaviours and improved flying capabilities in these reptiles. Pterosaur neuroanatomy, is known from just a few three-dimensionally preserved braincases of non-pterodactyloids (as Rhamphorhynchidae) and pterodactyloids, between which there is a large morphological gap. Here we report on a new Jurassic pterosaur from Argentina, Allkaruen koi gen. et sp. nov., remains of which include a superbly preserved, uncrushed braincase that sheds light on the origins of the highly derived neuroanatomy of pterodactyloids and their close relatives. A µCT ray-generated virtual endocast shows that the new pterosaur exhibits a mosaic of plesiomorphic and derived traits of the inner ear and neuroanatomy that fills an important gap between those of non-monofenestratan breviquartossans (Rhamphorhynchidae) and derived pterodactyloids. These results suggest that, while modularity may play an important role at one anatomical level, at a finer level the evolution of structures within a module may follow a mosaic pattern.
The inference of phylogenetic hypotheses from landmark data has been questioned during the last two decades. Besides theoretical concerns, one of the limitations pointed out for the use of landmark data in phylogenetics is its (supposed) lack of information relevant to the inference of phylogenetic relationships. However, empirical analyses are scarce; there exists no previous study that systematically evaluates the phylogenetic performance of landmark data in a series of data sets. In the present study, we analysed 41 published data sets in order to assess the correspondence between the phylogenetic trees derived from landmark data and those obtained with alternative and independent sources of evidence, and determined the main factors that might affect this inference. The data sets presented a variable number of terminals (5–200) and configurations (1–14), belonging to different taxonomic groups. The results showed that for most of the data sets analysed, the trees derived from landmark data presented a low correspondence with the reference phylogenies. The results were similar irrespective of the phylogenetic method considered. Complementary analyses strongly suggested that the limited amount of evidence included in each data set (one or a few landmark configurations) is the main cause for that low correspondence: the phylogenetic analysis of eight data sets that presented three or more configurations clearly showed that the inclusion of several landmark configurations improves the results. In addition, the analyses indicated that the inclusion of landmark data from different configurations is more important than the inclusion of more landmarks from the same configuration. Based on the results presented here, we consider that the poor results previously obtained in phylogenetic analyses based on landmark data were not caused by methodological limitations, but rather due to the limited amount of evidence included in the data sets.
Pterosaurs, a Mesozoic group of flying archosaurs, have become a focal point for debates pertaining to the impact of sampling biases on our reading of the fossil record, as well as the utility of sampling proxies in palaeo-diversity reconstructions. The completeness of the pterosaur fossil specimens themselves potentially provides additional information that is not captured in existing sampling proxies, and might shed new light on the group's evolutionary history. Here we assess the quality of the pterosaur fossil record via a character completeness metric based on the number of phylogenetic characters that can be scored for all known skeletons of 172 valid species, with averaged completeness values calculated for each geological stage. The fossil record of pterosaurs is observed to be strongly influenced by the occurrence and distribution of Lagerstätten. Peaks in completeness correlate with Lagerstätten deposits, and a recovered correlation between completeness and observed diversity is rendered non-significant when Lagerstätten species are excluded. Intervals previously regarded as potential extinction events are shown to lack Lagerstätten and exhibit low completeness values: as such, the apparent low diversity in these intervals might be at least partly the result of poor fossil record quality. A positive correlation between temporal patterns in completeness of Cretaceous pterosaurs and birds further demonstrates the prominent role that Lagerstätten deposits have on the preservation of smaller bodied organisms, contrasting with a lack of correlation with the completeness of large-bodied sauropodomorphs. However, we unexpectedly find a strong correlation between sauropodomorph and pterosaur completeness within the Triassic-Jurassic, but not the Cretaceous, potentially relating to a shared shift in environmental preference and thus preservation style through time. This study highlights the importance of understanding the relationship between various taphonomic controls when correcting for sampling bias, and provides additional evidence for the prominent role of sampling on observed patterns in pterosaur macroevolution.
Appendicular skeletal traits are used to quantify changes in morphological disparity and morphospace occupation across the fish-tetrapod transition and to explore the informativeness of different data partitions in phylogeny reconstruction. Anterior appendicular data yield trees that differ little from those built from the full character set, whilst posterior appendicular data result in considerable loss of phylogenetic resolution and tree branch rearrangements. Overall, there is a significant incongruence in the signals associated with pectoral and pelvic data. The appendicular skeletons of fish and tetrapods attain similar levels of morphological disparity (at least when data are rarefied at the maximum sample size for fish in our study) and occupy similarly sized regions of morphospace. However, fish appear more dispersed in morphospace than tetrapods do. All taxa show a heterogeneous distribution in morphospace, and there is a clear separation between fish and tetrapods despite the presence of several evolutionarily intermediate taxa.
Xiphosurids are an archaic group of aquatic chelicerate arthropods, generally known by the colloquial misnomer of 'horseshoe crabs'. Known from marine environments as far back as the early Ordovician, horseshoe crabs are generally considered 'living fossils' - descendants of a bradytelic lineage exhibiting little morphological or ecological variation throughout geological time. However, xiphosurids are known from freshwater sediments in the Palaeozoic and Mesozoic; furthermore, the contention that xiphosurids show little morphological variation has never been tested empirically. Attempts to test this are hampered by the lack of a modern phylogenetic framework with which to explore different evolutionary scenarios. Here, I present a phylogenetic analysis of Xiphosurida and explore patterns of morphospace and environmental occupation of the group throughout the Phanerozoic. Xiphosurids are shown to have invaded non-marine environments independently at least five times throughout their evolutionary history, twice resulting in the radiation of major clades - bellinurines and austrolimulids - that occupied novel regions of morphospace. These clades show a convergent ecological pattern of differentiation, speciation and subsequent extinction. Horseshoe crabs are shown to have a more dynamic and complex evolutionary history than previously supposed, with the extant species representing only a fraction of the group's past ecological and morphological diversity.
It is important to quantify patterns of morphological diversity to enhance our understanding of variation in ecological and evolutionary traits. Here, we present a quantitative analysis of morphological diversity in a family of small mammals, the tenrecs (Afrosoricida, Tenrecidae). Tenrecs are often cited as an example of an exceptionally morphologically diverse group. However, this assumption has not been tested quantitatively. We use geometric morphometric analyses of skull shape to test whether tenrecs are more morphologically diverse than their closest relatives, the golden moles (Afrosoricida, Chrysochloridae). Tenrecs occupy a wider range of ecological niches than golden moles so we predict that they will be more morphologically diverse. Contrary to our expectations, we find that tenrec skulls are only more morphologically diverse than golden moles when measured in lateral view. Furthermore, similarities among the species-rich Microgale tenrec genus appear to mask higher morphological diversity in the rest of the family. These results reveal new insights into the morphological diversity of tenrecs and highlight the importance of using quantitative methods to test qualitative assumptions about patterns of morphological diversity.
The distinctly non-random diversity of organismal form manifests itself in discrete clusters of taxa that share a common body plan. As a result, analyses of disparity require a scalable comparative framework. The difficulties of applying geometric morphometrics to disparity analyses of groups with vastly divergent body plans are overcome partly by the use of cladistic characters. Character-based disparity analyses have become increasingly popular, but it is not clear how they are affected by character coding strategies or revisions of primary homology statements. Indeed, whether cladistic and morphometric data capture similar patterns of morphological variation remains a moot point. To address this issue, we employ both cladistic and geometric morphometric data in an exploratory study of disparity focussing on caecilian amphibians. Our results show no impact on relative intertaxon distances when different coding strategies for cladistic characters were used or when revised concepts of homology were considered. In all instances, we found no statistically significant difference between pairwise Euclidean and Procrustes distances, although the strength of the correlation among distance matrices varied. This suggests that cladistic and geometric morphometric data appear to summarize morphological variation in comparable ways. Our results support the use of cladistic data for characterizing organismal disparity.
New remains of an azhdarchid pterosaur were discovered from the Upper Cretaceous (Santonian) Csehbánya Formation at the Iharkút vertebrate locality in the Bakony Mountains, western Hungary. Among the isolated bones, consisting principally of 21 symphyseal jaw fragments, four cervical vertebrae, a right radius, and some fragmentary limb bones, is a complete articulated mandible that represents one of the best-preserved mandibular material of any presently known azhdarchid pterosaur. The complete edentulous jaw, referred to Bakonydraco galaczi gen. et sp. nov. posesses several features diagnostic for azhdarchids which prove that Bakonydraco belongs to this group. The cervical vertebrae exhibit azhdarchid features and consequently are referred to as Azhdarchidae indet. The discovery of these fossils helps to understand the construction of the azhdarchid mandible and provides new insight for studying the feeding style of the edentulous azhdarchid pterosaurs.
Efforts to establish the masses of pterosaurs have been attempted for almost a century, but the methods employed are often as problematic as their conclusions that pterosaurs are unusually lightweight. Historically, most pterosaur masses have been determined through geometric modelling of pterosaur bodies and extrapolation of body densities from modern birds. However, both ecology and flight style are known to induce variation of body density across modern bird species, casting doubt on this frequently used method. Here, a new approach to mass estimation is attempted that requires no assumption of soft tissue density or distribution: following observations that the relationship of dry skeletal mass to body mass is essentially identical in ecologically and phylogenetically disparate modern birds and mammals, the skeletal masses of 19 pterosaur taxa have been estimated and their body masses regressed from the relationship between skeletal mass and body mass in modern forms. Masses derived from this method are up to three times greater than those estimated in previous studies with the largest pterosaur in this investigation (wingspan 10 m) found to have a mass of 250 kg. Reappraisal of pterosaur masses shows that lightweight pterosaur mass estimates are considerably lower than those of similarly sized birds and bats, requiring inordinate amounts of pneumaticity (up to 90 per cent for the lowest estimates of the largest forms) and are wholly unrealistic in light of the enormous sizes achieved by some pterosaurs. Combining heavier mass data with restorations of pterosaur wings based on preserved wing membranes permits assessment of basic pterosaur flight characteristics. Preserved wing membranes suggest that ankle-attached brachiopatagia are the best supported pterosaur wing model, and distinctions in forelimb/hindlimb ratios produce a range of wing shapes despite a standardised brachiopatagia configuration. Plotting greater masses and ankle-attached wings into a principal component analysis of aspect ratio and wing loading demonstrates that pterosaurs had a range of flight styles similar to those seen in modern volant vertebrates. A broad spectrum of pterosaur flight styles are predicted including marine and thermal soarers, adaptive generalists and forms for which flight is energetically costly and expensive.
Assessing the quality of the fossil record is notoriously hard, and many recent attempts have used sampling proxies that can be questioned. For example, counts of geological formations and estimated outcrop areas might not be defensible as reliable sampling proxies: geological formations are units of enormously variable dimensions that depend on rock heterogeneity and fossil content (and so are not independent of the fossil record), and outcrop areas are not always proportional to rock exposure, probably a closer indicator of rock availability. It is shown that in many cases formation counts will always correlate with fossil counts, whatever the degree of sampling. It is not clear, in any case, that these proxies provide a good estimate of what is missing in the gap between the known fossil record and reality; rather they largely explore the gap between known and potential fossil records. Further, using simple, single numerical metrics to correct global-scale raw data, or to model sampling-driven patterns may be premature. There are perhaps four approaches to exploring the incompleteness of the fossil record, (1) regional-scale studies of geological completeness; (2) regional- or clade-scale studies of sampling completeness using comprehensive measures of sampling, such as numbers of localities or specimens or fossil quality; (3) phylogenetic and gap-counting methods; and (4) model-based approaches that compare sampling as one of several explanatory variables with measures of environmental change, singly and in combination. We suggest that palaeontologists, like other scientists, should accept that their data are patchy and incomplete, and use appropriate methods to deal with this issue in each analysis. All that matters is whether the data are adequate for a designated study or not. A single answer to the question of whether the fossil record is driven by macroevolution or megabias is unlikely ever to emerge because of temporal, geographical, and taxonomic variance in the data.
Recently, there has been much interest in detecting and measuring patterns of change in disparity. Although most studies have used one or two measures of disparity to quantify and characterize the occupation of morphospace, multiple measures may be necessary to fully detect changes in patterns of morphospace occupation. Also, the ability to detect morphological trends and occupation patterns within morphospace depends on using the appropriate measure(s) of dis- parity. In this study, seven measures were used to determine and characterize sensitivity to sample size of the data, number of morphological characters, percentage of missing data, and changes in morphospace occupation pattern. These consist of five distance measures—sum of univariate var- iances, total range, mean distance, principal coordinate analysis volume, average pairwise dissim- ilarity—and two non-distance measures—participation ratio and number of unique pairwise char- acter combinations. Evaluation of each measure with respect to sensitivity to sample size, number of morphological characters, and percentage of missing data was accomplished by using both sim- ulated and Ordovician crinoid data. For simulated data, each measure of disparity was evaluated for its response to changes of morphospace occupation pattern, and with respect to simulated ran- dom and nonrandom extinction events. Changes in disparity were also measured within the Cri- noidea across the Permian extinction event. Although all measures vary in sensitivity with respect to species sample size, number of mor- phological characters, and percentage of missing data, the non-distance measures overall produce the lowest estimates of variance (in bootstrap analyses). The non-distance measures appear to be relatively insensitive to changes in morphospace occupation pattern. All measures, except average pairwise dissimilarity, detect changes in occupation pattern in simulated nonrandom extinction events, but all measures, except number of unique pairwise character combinations and principal coordinate analysis volume, are relatively insensitive to changes in pattern in simulated random extinction events. The distance measures report similar changes in disparity over the Permian ex- tinction event, whereas the non-distance measures differ. This study suggests that each measure of disparity is designed for different purposes, and that by using a combination of techniques a clearer picture of disparity should emerge.
New specimens of pterosaurs with soft-part preservation from the Solnhofen Lithographic Limestone (S Germany) and the Crato Formation (northeastern Brazil) yield hitherto unknown and unexpected details of pterosaur anatomy: the presence and internal anatomy of soft-tissue crests, the internal anatomy of the brachiopatagium, including a blood vessel system and structural details of foot and hand. Some consequences for pterosaurian flight, thermoregulation and aspects of evolution are discussed.
A new rhamphorhynchid pterosaur species, Sericipterus wucaiwanensis, gen. et sp. nov., is described from the Upper Jurassic part of the Shishugou Formation in the Xinjiang Autonomous Region of northwest China. Pterosaurs from this unit are the earliest and only records of pterosaurs in the Jurassic of northwest China. The individual specimen is one of the largest known among ‘rhamphorhynchoids,’ or non-pterodactyloid pterosaurs. The holotype comprises an associated skeleton of mostly disarticulated, largely three-dimensional material. Although partly crushed, the preservation in this specimen reveals morphology rarely seen in non-pterodactyloid pterosaurs. This includes a distinct cervical intervertebral articulation morphology that is proposed to be widespread among the non-pterodactyloids. The skull of this new specimen is most similar to that of other rhamphorhynchids, Angustinaripterus longicephalus and Harpactognathus gentryii, found in terrestrial deposits. A phylogenetic analysis of 18 non-pterodactyloid pterosaurs and the Pterodactyloidea places Sericipterus wucaiwanensis with these species within the Rhamphorhynchinae and a monophyletic Rhamphorhynchidae. Unlike previous phylogenetic analyses, the Dimorphodontidae is paraphyletic, the Campylognathoididae is polyphyletic, and the Anurognathidae is the sister group of the Pterodactyloidea. Sericipterus wucaiwanensis, Angustinaripterus longicephalus, Harpactognathus gentryii represent a clade of large pterosaurs that likely lived in the terrestrial settings in which they preserved.
Pterosaurs were important flying vertebrates for most of the Mesozoic, from the Late Triassic to the end of the Cretaceous (225–65 Ma). They varied enormously through time in overall size (with wing spans from about 250 mm to about 12 m), and in features of their cranial and postcranial skeletons. Comparisons of disparity based on discrete cladistic characters show that the basal paraphyletic rhamphorhynchoids (Triassic–Early Cretaceous) occupied a distinct, and relatively small, region of morphospace compared to the derived pterodactyloids (Late Jurassic–Late Cretaceous). This separation is unexpected, especially in view of common constraints on anatomy caused by the requirements of flight. Pterodactyloid disparity shifted through time, with different, small portions of morphospace occupied in the Late Jurassic and Late Cretaceous, and a much larger portion in the Early Cretaceous. This explosion in disparity after 100 Ma of evolution is matched by the highest diversity of the clade: evidently, pterosaurs express a rather ‘top heavy’ clade shape, and this is reflected in delayed morphological evolution, again an unexpected finding. The expansion of disparity among pterodactyloids was comparable across subclades: pairwise comparisons among the four pterodactyloid superfamilies show that, for the most part, these clades display significant morphological separation, except in the case of Dsungaripteroidea and Azhdarchoidea. Finally, there is no evidence that rhamphorhynchoids as a whole were outcompeted by pterodactyloids, or that pterosaurs were driven to extinction by the rise of birds.
The analysis of shape is a fundamental part of much biological research. As the field of statistics developed, so have the sophistication of the analysis of these types of data. This lead to multivariate morphometrics in which suites of measurements were analyzed together using canonical variates analysis, principal components analysis, and related methods. In the 1980s, a fundamental change began in the nature of the data gathered and analyzed. This change focused on the coordinates of landmarks and the geometric information about their relative positions. As a by‐product of such an approach, results of multivariate analyses could be visualized as configurations of landmarks back in the original space of the organism rather than only as statistical scatter plots. This new approach, called “geometric morphometrics”;, had benefits that lead Rohlf and Marcus (1993) to proclaim a “revolution”; in morphometrics. In this paper, we briefly update the discussion in that paper and summarize the advances in the ten years since the paper by Rohlf and Marcus. We also speculate on future directions in morphometric analysis.
The quantification of disparity is an important aspect of recent macroevolutionary studies, and it is usually motivated by theoretical considerations about the pace of innovation and the filling of morphospace. In practice, varying protocols of data collection and analysis have rendered comparisons among studies difficult. The basic question remains, How sensitive is any given disparity signal to different aspects of sampling and data analysis? Here we explore this issue in the context of the radiation of the echinoid order Spatangoida during the Cretaceous. We compare patterns at the genus and species levels, with time subdivision into subepochs and into stages, and with morphological sampling based on landmarks, traditional morphometrics, and discrete characters. In terms of temporal scale, similarity of disparity pattern accrues despite a change in temporal resolution, and a general deceleration in morphological diversification is apparent. Different morphometric methods also produce similar signals. Both the landmark analysis and the discrete character analysis suggest relatively high early disparity, whereas the analysis based on traditional morphometrics records a much lower value. This difference appears to reflect primarily the measurement of different aspects of overall morphology. Disparity patterns are similar at both the genus and species levels. Moreover, inclusion or exclusion of the sister order Holasteroida and the stem group Disasteroida in the sampled morphospace did not affect proportional changes in spatangoid disparity. Similar results were found for spatangoid subclades vis-à-vis spatangoids as a whole. The relative robustness of these patterns implies that the choice of temporal scale, morphometric scheme, and taxonomic level may not affect broad trends in disparity and the representation of large-scale morphospace structure.
The analysis of morphological disparity and of morphospace occupation through the macroevolutionary history of clades is now a major research program in paleobiology, and increas-ingly so in organismal and comparative biology. Most studies have focused on the relationship between taxonomic diversity and morphological disparity, and on ecological or developmental con-trols. However, the geographic context of diversification has remained understudied. Here we ad-dress geography quantitatively. Diversity, disparity, and paleogeographic dispersion are used to describe the evolutionary history of an extinct echinoderm clade, the class Stylophora (cornutes, mitrates), from the Middle Cambrian to the Middle Devonian (about 128 Myr subdivided into 12 stratigraphic intervals). Taxonomic diversity is estimated from a representative sample including 73.3% of described species and 92.4% of described genera. Stylophoran morphology is quantified on the basis of seven morphometric parameters derived from image analysis of homologous skel-etal regions. Three separate principal coordinates analyses (PCO) are performed for thecal outlines, plates from the lower thecal surface, and plates from the upper thecal surface, respectively. PCO scores from these three separate analyses are then used as variables for a single, global, meta-PCO. For each time interval, disparity is calculated as the sum of variance in the multidimensional mor-phospace defined by the meta-PCO axes. For each time interval, a semiquantitative index of paleo-geographic dispersion is calculated, reflecting both global (continental) and local (regional) aspects of dispersion. Morphospace occupation of cornutes and mitrates is partly overlapping, suggesting some mor-phologic convergences between the two main stylophoran clades, probably correlated to similar modes of life (e.g., symmetrical cornutes and primitive mitrocystitids). Hierarchical clustering al-lowed the identification of three main morphological sets (subdivided into 11 subsets) within the global stylophoran morphospace. These morphological sets are used to analyze the spatiotemporal variations of disparity. The initial radiation of stylophorans is characterized by a low diversity and a rapid increase in disparity (Middle Cambrian–Tremadocian). The subsequent diversification in-volved filling and little expansion of morphospace (Arenig–Middle Ordovician). Finally, both sty-lophoran diversity and disparity decreased relatively steadily from the Late Ordovician to the Mid-dle Devonian, with the exception of a second (lower) peak in the Early Devonian. Such a pattern is comparable to that of other Paleozoic marine invertebrates such as blastozoans and orthid bra-chiopods. During the Lower to Middle Ordovician, the most dramatic diversification of stylo-phorans took place with a paleogeographic dispersion essentially limited to the periphery of Gond-wana. In the Late Ordovician, stylophorans steadily extended toward lower paleolatitudes, and new environmental conditions, where some of them radiated, and finally survived the end-Ordo-vician mass extinction (e.g., anomalocystitids). This pattern of paleobiogeographic dispersion is comparable to that of other examples of Paleozoic groups of marine invertebrates, such as bivalve mollusks.
Perhaps the most iconic of pterosaurs is the Late Cretaceous Pteranodon, known for its large wing span of up to 5.6 m or more and a remarkable long bony crest at the back of the head. The function of this crest has been the subject of much controversy, having been interpreted as an aerodynamically beneficial structure, perhaps acting as an airbrake, a forward rudder, or a counterbalance to the beak. In this paper these hypotheses are tested by experimenting on cranial models of both P. longiceps and its close relative P. steinbergi in a wind tunnel and comparing the results against a crestless control model, The results show that, while a crest assists in lowering the yawing moment of the head and limiting the movement of the centre of pressure, the overall aerodynamic effect is modest. The crest most probably evolved independently of any aerodynamic function, other than to maintain their streamlined profile for reducing drag, and presumably served primarily in either intraspecific sexual displays and/or species recognition.
The size and flight mechanics of giant pterosaurs have received considerable research interest for the last century but are confused by conflicting interpretations of pterosaur biology and flight capabilities. Avian biomechanical parameters have often been applied to pterosaurs in such research but, due to considerable differences in avian and pterosaur anatomy, have lead to systematic errors interpreting pterosaur flight mechanics. Such assumptions have lead to assertions that giant pterosaurs were extremely lightweight to facilitate flight or, if more realistic masses are assumed, were flightless. Reappraisal of the proportions, scaling and morphology of giant pterosaur fossils suggests that bird and pterosaur wing structure, gross anatomy and launch kinematics are too different to be considered mechanically interchangeable. Conclusions assuming such interchangeability--including those indicating that giant pterosaurs were flightless--are found to be based on inaccurate and poorly supported assumptions of structural scaling and launch kinematics. Pterosaur bone strength and flap-gliding performance demonstrate that giant pterosaur anatomy was capable of generating sufficient lift and thrust for powered flight as well as resisting flight loading stresses. The retention of flight characteristics across giant pterosaur skeletons and their considerable robustness compared to similarly-massed terrestrial animals suggest that giant pterosaurs were not flightless. Moreover, the term 'giant pterosaur' includes at least two radically different forms with very distinct palaeoecological signatures and, accordingly, all but the most basic sweeping conclusions about giant pterosaur flight should be treated with caution. Reappraisal of giant pterosaur material also reveals that the size of the largest pterosaurs, previously suggested to have wingspans up to 13 m and masses up to 544 kg, have been overestimated. Scaling of fragmentary giant pterosaur remains have been misled by distorted fossils or used inappropriate scaling techniques, indicating that 10-11 m wingspans and masses of 200-250 kg are the most reliable upper estimates of known pterosaur size.
An analysis of the structure and kinematics of the forelimbs and hindlimbs of pterosaurs, and functional analogy with recent and fossil vertebrates, supports a reappraisal of the locomotory abilities of pterosaurs. A hypothesis of structural, aerodynamic, and evolutionary differences distinguishing vertebrate gliders from fliers is proposed; pterosaurs fit all the criteria of fliers but none pertaining to gliders. The kinematics of the reconstructed pterosaur flight stroke reveal a down-and-forward component found also in birds and bats; structural features of the shoulder girdle and sternum unique to pterosaurs may be explained in light of this motion. The recovery stroke of flight was accomplished, in birdlike fashion, by a functional reversal of the action of the M. supracoracoideus by the pronounced enlargement of the acrocoracoid process, which acted as a pulley. The wing membrane was supported and controlled through a system of stiffened, intercalated fibers, which were oriented like the main structural elements in the wings of birds and bats.
The hindlimbs of pterosaurs were independent of the wing membrane, and articulated like those of other advanced archosaurs and birds, not like those of bats. The gait was parasagittal and the stance digitigrade. Because of limitations on the motion of the forelimb at the shoulder, pterosaurs could not have walked quadrupedally. However, bipedal locomotion appears to have been normal and quite sufficient in all pterosaurs. There is nothing batlike about pterosaur anatomy; on the other hand, pterosaurs bear close structural resemblances to birds and dinosaurs, to which they are most closely related phylogenetically.
The paper documents evolutionary patterns of morphological disparity in Ordovician-Devonian crinoids, using a set of 75 discrete characters covering the principal features of the crinoid stem, cup, tegmen, and arms. Discrepancy is measured as the average dissimilarity among species, the range of morphospace occupied, and the number of realized character-state combinations. Comparison with generic richness reveals that the full range of form was essentially attained by the early part of the Caradocian, long before the time of maximal taxonomic diversity. Despite subsequent taxonomic diversification, the variety of crinoid form did not expand appreciably; increased diversity was accommodated by the evolution of variations upon the spectrum of designs established earlier. -from Author
The Cambrian Radiation marks the appearance of representatives of virtually all major skeletonized phyla in the fossil record and clearly represents a fundamental episode in the history of life. Furthermore, the tempo and mode of this evolutionary event have been the subject of intense debate. One area that has been debated is how so many phylum-level body plans can have evolved in such a geologically brief period. Some have argued that there was enhanced morphological flexibility and fewer evolutionary constraints at this time, leading to greater morphological disparity of Early Cambrian faunas. Others have claimed that this is not true because the evolution of most of the animal phyla significantly predates the radiation or because they failed to detect a signature of decreasing morphological disparity through time. At present, the higher-level patterns of diversification during this time period and the relevant implications for Early Cambrian uniqueness are areas of active research interest and debate. Recognizing this debate, we used both a phylogenetic and a morphometric framework to study whether there is a signature of increasing morphological constraint and decreasing flexibility through time within one of the clades that is a significant constituent of the Early Cambrian biota, specifically, the olenelloid trilobites. In this species-rich clade, we found no evidence that morphological changes were becoming either increasingly constrained or less flexible in one of the dominant Early Cambrian metazoan clades as it passed through the Cambrian Radiation.
The origin of flight can be approached through a combination of phylogenetic, functional, and aerodynamic evidence. A basic question is whether flight evolved in the trees or on the ground. Of the three groups of active flyers, two (pterosaurs and birds) show no trace of gliding antecedents and appear to have evolved flight directly from the ground. Bats show many morphological and phylogenetic indications of an arboreal, gliding ancestry and are very different in all such respects from pterosaurs and birds. Pterosaurs were structurally and functionally convergent on birds in many locomotory respects, and show prima-facie evidence of a cursorial, non-gliding origin of flight. Aerodynamic considerations of extinct vertebrates have mainly focused on two animals: Archaeopteryx (the first known bird) and Pteranodon (a specialized Cretaceous pterosaur). Functional inferences from skeletal evidence imply that Archaeopteryx was capable of flapping flight, though most 'modern' avian flight features were not developed; it does not seem well built for gliding. Pteranodon (a soarer, not a glider), like many large birds was capable of active flight but probably only used it to take off, gain altitude, and avert danger. All pterosaurs were strong, active fliers and only large size constrained this ability. Reappraisal of the anatomy and aerodynamic parameters indicate that Pteranodon's flight range was higher and that it was more active and manoeuverable than previous studies have suggested, and so more comparable to modern soaring birds. Studies of flight in extinct organisms cannot rely solely on engineering models or presumed selective advantages or pressures; they must take into consideration all aspects of phylogeny, function, and aerodynamics.from Author
A maximum parsimony analysis of a data matrix including 42 temnospondyl species and 14 outgroup species coded for 246 characters results in eight shortest trees. Temnospondyls emerge as two distinct radiations: one includes edopoids and eryopoids-basal archegosauriforms; the other includes dissorophoids and dvinosaurs. Both receive low statistical support. The branching pattern of dissorophoids remains elusive and is obscured by recurrent homoplasies. The two Micropholis morphs appear as sister taxa near the base of the dissorophoid clade. Perryella is either placed as sister taxon to dvinosaurs or nested within them. Temnospondyls such as the genera Balanerpeton and Dendrerpeton occur close to the node that subtends the dvinosaur-dissorophoid separation. Disparity analysis using Principal Coordinate Analysis of both Manhattan and Euclidean intertaxon distance matrices reveals that all major temnospondyl groups are widely separated in morphospace. Levels of disparity are comparable in the various clades examined, but the dvinosaurs tend to be morphologically more diverse than other groups when variance-derived metrics are used. For range-derived metrics, dissorophoids are more disparate than other groups. Overall disparity is similar in edopopids and eryopoids-basal archegosauriforms, as is in dissorophoids and dvinosaurs. However, the latter two groups are invariably slightly more disparate than the former two.
The Cretaceous angiosperm radiation offers an opportunity to examine patterns of morphological evolution in terrestrial plants and to compare them with patterns previously observed during radiations of marine animals. Focusing on evolution among angiosperm pollen types, I used average pairwise dissimilarity and total variance to describe changing morphological varieties (disparity) through the Cretaceous and Paleocene in North America. Angiosperm species diversity shows an approximately tenfold increase through this interval, but this taxonomic diversification is not matched by a comparable change in morphological disparity. Partitioning of morphological disparity among major pollen groups shows that most of the variance is contributed by eudicots from the Albian onwards. Constant disparity across the Cretaceous/Tertiary boundary despite decreased taxonomic diversity suggests that the Cretaceous/Tertiary extinction was not selective with respect to the pollen morphological characters analyzed here. The two measures of disparity show similar patterns. The overall pattern is robust to changes in character weighting, indicating that no one set of characters or weighting scheme is driving the pattern. Analyses of older data indicate that the initial burst of disparity in the Aptian could be due in part to analytical time-averaging. The observed incongruence between taxonomic diversity and morphological disparity suggests that morphological evolution in pollen was characterized by larger jumps early and smaller jumps later on, and it similar to that found in several groups of marine invertebrates.
Pterosaurs first appeared in the Late Triassic and persisted until the terminal Cretaceous: they achieved a global distribution during the Mesozoic. Here, we attempt to provide the first comprehensive summary of pterosaur distribution through time and space, including information on the taxonomie composition of pterosaur faunas and the lithostratigraphic units in which they occur. We hope that this compilation will be used as a primary research tool, permitting more detailed and rigorous analyses of pterosaur diversity and palaeobiogeography than have been possible to date.
Paleontologists and biologists are often interested in the tempo of evolution: how fast or slow does evolution proceed? There are many separate components of evolution – the development and extinction of lineages, molecular change, and morphological transformation are three of the most general – and these may or may not be related to each other. Therefore, it is instructive to look at each of these separately (if possible), in order to gain a more nuanced understanding of evolutionary change. This chapter will focus specifically on morphological evolution: changes in size, shape, and discrete anatomical features and how rates of change can be calculated. Such calculations have a rich legacy in the macroevolution literature (e.g., Westoll 1949; Derstler 1982; Forey 1988; Cloutier 1991; Ruta et al. 2006; Brusatte et al. 2008a).
A direct algorithm is described to reconstruct on a phylogenetic tree the ancestral states of a continuous-valued character, using a parsimony criterion that minimizes the sum of squared changes along the branches. It is shown that when the squared changes are inversely weighted by the lengths of the branches, the squared-change parsimony reconstruction is that which has maximum posterior probability under a Brownian motion model of evolution. The squared-change parsimony estimates are also closely related to the contrasts in Felsenstein's test of character correlation.
Geometric Morphometrics for Biologists is an introductory textbook for a course on geometric morphometrics, written for graduate students and upper division undergraduates, covering both theory of shape analysis and methods of multivariate analysis. It is designed for students with minimal math background; taking them from the process of data collection through basic and more advanced statistical analyses. Many examples are given, beginning with simple although realistic case-studies, through examples of complex analyses requiring several different kinds of methods. The book also includes URLâs for free software and step-by-step instructions for using the software.
Increasingly, data on shape are analysed in combination with molecular genetic or ecological information, so that tools for geometric morphometric analysis are required. Morphometric studies most often use the arrangements of morphological landmarks as the data source and extract shape information from them by Procrustes superimposition. The MorphoJ software combines this approach with a wide range of methods for shape analysis in different biological contexts. The program offers an integrated and user-friendly environment for standard multivariate analyses such as principal components, discriminant analysis and multivariate regression as well as specialized applications including phylogenetics, quantitative genetics and analyses of modularity in shape data. MorphoJ is written in Java and versions for the Windows, Macintosh and Unix/Linux platforms are freely available from http://www.flywings.org.uk/MorphoJ_page.htm.
During the last 10 years numerical methods have begun to dominate paleontology. These methods now reach far beyond the fields of morphological and phylogenetic analyses to embrace biostratigraphy, paleobiogeography, and paleoecology. Paleontological Data Analysis explains the key numerical techniques in paleontology, and the methodologies employed in the software packages now available. Following an introduction to numerical methodologies in paleontology, and to univariate and multivariate techniques (including inferential testing), there follow chapters on morphometrics, phylogenetic analysis, paleobiogeography and paleoecology, time series analysis, and quantitative biostratigraphy Each chapter describes a range of techniques in detail, with worked examples, illustrations, and appropriate case histories Describes the purpose, type of data required, functionality, and implementation of each technique, together with notes of caution where appropriate The book and the accompanying PAST software package (seewww.blackwellpublishing.com/hammer) are important investigative tools in a rapidly developing field characterized by many exciting new discoveries and innovative techniques An invaluable tool for all students and researchers involved in quantitative paleontology.
Body masses for 14 species of pterosaur spanning four orders of magnitude were estimated using three-dimensional, digital models. The modeled taxa comprised seven paraphyletic ‘rhamphorhynchoids’: Anurognathus ammoni, Dimorphodon macronyx, Eudimorphodon ranzii, Jeholopterus ningchengensis, Preondactylus buffarinii, Rhamphorhynchus muensteri, and Sordes pilosus; and seven pterodactyloids: Anhanguera santanae, Dsungaripterus weii, Pteranodon longiceps, Pterodaustro guinazui, Pterodactylus sp., Quetzalcoatlus northropi, Tupuxuara longicristatus. The reliability of the mass estimation methods were tested with equivalent models of six extant species of bird with masses that spanned three orders of magnitude. The close agreement between model bird mass estimates and those of the living forms provides a level of confidence in the results obtained for the extinct pterosaurs. The masses of the axial body regions (tail, trunk, neck, head), limbs, and patagia of the pterosaurs were individually estimated and distinct differences in relative body proportions were found between species. Allometric relationships between body length and wingspan and body mass were derived for ‘rhamphorhynchoids’ and pterodactyloids to facilitate the estimation of body masses for other pterosaurs known from incomplete material, and these relationships also highlight differences in phyletic shape change between the two groups. The estimated mass for the largest pterosaur known, Quetzalcoatlus northropi, exceeds the previous highest estimates by more than 100%, and it is argued that this extremely large pterosaur is better interpreted as a secondarily flightless form.
Pterosaurs were the first flying vertebrates and formed important components of terrestrial and marginal marine ecosystems during the Mesozoic. They became extinct during the latest Cretaceous (latest Maastrichtian), at, or near, the Cretaceous/Paleogene boundary, following an apparent decline in diversity in the Late Cretaceous. This reduction in species richness has been linked to the ecological radiation of birds in the Early Cretaceous and the proposal that birds competitively excluded pterosaurs from many key niches. However, although competition is often posited as a causal mechanism for many of the clade-clade replacements observed in the fossil record, these hypotheses are rarely tested. Here we present a detailed examination of pterosaur diversity through time, including both taxic and phylogenetically corrected diversity estimates and comparison of these estimates with a model describing temporal variation in the number of pterosaur-bearing formations (a proxy for rock availability). Both taxic and phylogenetic diversity curves are strongly correlated with numbers of pterosaur-bearing formations, suggesting that a significant part of the signal contained within pterosaur diversity patterns may be controlled by geological and taphonomic megabiases rather than macroevolutionary processes. There is no evidence for a long-term decline in pterosaur diversity through the Cretaceous, although a reduction in morphological, ecological, and phylogenetic diversity does appear to have occurred in the latest Cretaceous. Competitive replacement of pterosaurs by birds is difficult to support on the basis of diversity patterns.
Disparity is a measure of the range or significance of morphology in a given sample of organisms, as opposed to diversity, which is expressed in terms of the number (and sometimes ranking) of taxa. At present there is no agreed definition of disparity, much less any consensus on how to measure it. Two possible categories of metric are considered here, one independent of any hypothesis of relationship (phenetics), the other constrained within an evolutionary framework (cladistics).
The Early Cambrian radiation was clearly a period of significant morphologic and taxonomic diversification. However, we question the interpretation of its first generation products as numerous body plans at the highest level. Four phenetic and two cladistic measures have been used to compare disparity among Cambrian arthropods with that in the living fauna. Phenetic methods assessing character-state variability and the amount of morphological attribute space occupied yield similar results for Cambrian and Recent arthropods. Assessments of disparity within a taxonomic framework rely on the identification of particular characters that delineate higher level body plans. This requires a phylogenetic interpretation, a cladistic investigation of hierarchical structure in the data. Both sets of arthropods fall within the same major clades, and within this cladistic framework the amount of character-state evolution in the two groups is comparable. None of these methods identifies markedly greater disparity among the Cambrian compared with the Recent taxa.
Although measures of disparity are applied here to a consideration of the Cambrian radiation, the metrics clearly have a much wider potential for estimating macroevolutionary trends independently from existing taxonomic frameworks. Geometric morphometry is ideal for measuring morphological variety at lower taxonomic levels, but it requires the recognition of homologous landmarks in all the forms under comparison, or the identification of entire homologous structures. Conventional phenetics has much wider application as it can operate on data coded as discrete homologous character states (this facility is also a requirement of cladistics), which are a more appropriate basis for comparing disparity in markedly dissimilar forms.
-Morphological,and taxonomic,diversity each provide insight into the expansion,and contraction of major biological groups, while the nature of the relationship between these two aspects of diversity also has important implications for evolutionary mechanisms. In this paper, I compare morphological and taxonomic diversity within the classes Blastoidea and Trilobita, and within the trilobite clades Libristoma, Asaphina, Proetida, Phacopida, and Scutelluina. Blastoid morphology is quantified with homologous landmarks on the theca, and trilobite form is measured with a Fourier description of the cranidium. Morphological diversity is measured,as the total variance among,forms in morphological,space (proportional to the mean,squared distance among,forms). Blastoid taxonomic,diversity is based on published compilation of stratigraphic ranges of genera. The Zoological Record was used to determine the number,of new species of trilobites described since the publication of the Treatise; temporal patterns in species richness are similar to those for generic richness based on the Treatise, suggesting a common underlying signal. Morphological variety and taxonomic richness often increase together during the initial diver-
Morphometrics is the statistical study of biological shape and shape change. Its richest data are landmarks, points, such as the bridge of the nose, that have biological names as well as geometric locations. This book is the first systematic survey of morphometric methods for landmark data.
The first edition of Geometric Morphometrics for Biologists has been the primary resource for teaching modern geometric methods of shape analysis to biologists who have a stronger background in biology than in multivariate statistics and matrix algebra. These geometric methods are appealing to biologists who approach the study of shape from a variety of perspectives, from clinical to evolutionary, because they incorporate the geometry of organisms throughout the data analysis. The second edition of this book retains the emphasis on accessible explanations, and the copious illustrations and examples of the first, updating the treatment of both theory and practice. The second edition represents the current state-of-the-art and adds new examples and summarizes recent literature, as well as provides an overview of new software and step-by-step guidance through details of carrying out the analyses. Contains updated coverage of methods, especially for sampling complex curves and 3D forms and a new chapter on applications of geometric morphometrics to forensics Offers a reorganization of chapters to streamline learning basic concepts Presents detailed instructions for conducting analyses with freely available, easy to use software Provides numerous illustrations, including graphical presentations of important theoretical concepts and demonstrations of alternative approaches to presenting results.
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Hone, D.W.E., Naish, D. & Cuthill, I.C. 2011: Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia, Vol. 45, pp. 139–156.
Cranial ornamentation is widespread throughout the extinct non-avialian Ornithodira, being present throughout Pterosauria, Ornithischia and Saurischia. Ornaments take many forms, and can be composed of at least a dozen different skull bones, indicating multiple origins. Many of these crests serve no clear survival function and it has been suggested that their primary use was for species recognition or sexual display. The distribution within Ornithodira and the form and position of these crests suggest sexual selection as a key factor, although the role of the latter has often been rejected on the grounds of an apparent lack of sexual dimorphism in many species. Surprisingly, the phenomenon of mutual sexual selection – where both males and females are ornamented and both select mates – has been ignored in research on fossil ornithodirans, despite a rich history of research and frequent expression in modern birds. Here, we review the available evidence for the functions of ornithodiran cranial crests and conclude that mutual sexual selection presents a valid hypothesis for their presence and distribution. The integration of mutual sexual selection into future studies is critical to our understanding of ornithodiran ecology, evolution and particularly questions regarding sexual dimorphism. □Behaviour, Dinosauria, ornaments, Pterosauria, sexual selection.
Ősi, A. 2011: Feeding-related characters in basal pterosaurs: implications for jaw mechanism, dental function and diet. Lethaia, Vol. 44, pp. 136–152.A comparative study of various feeding-related features in basal pterosaurs reveals a significant change in feeding strategies during the early evolutionary history of the group. These features are related to the skull architecture (e.g. quadrate morphology and orientation, jaw joint), dentition (e.g. crown morphology, wear patterns), reconstructed adductor musculature and post-cranium. The most basal pterosaurs (Preondactylus, dimorphodontids and anurognathids) were small-bodied animals with a wingspan no greater than 1.5 m, a relatively short, lightly constructed skull, straight mandibles with a large gape, sharply pointed teeth and well-developed external adductors. The absence of extended tooth wear excludes complex oral food processing and indicates that jaw closure was simply orthal. Features of these basal-most forms indicate a predominantly insectivorous diet. Among stratigraphically older but more derived forms (Eudimorphodon, Carniadactylus, Caviramus) complex, multicuspid teeth allowed the consumption of a wider variety of prey via a more effective form of food processing. This is supported by heavy dental wear in all forms with multicuspid teeth. Typical piscivorous forms occurred no earlier than the Early Jurassic, and are characterized by widely spaced, enlarged procumbent teeth forming a fish grab and an anteriorly inclined quadrate that permitted only a relatively small gape. In addition, the skull became more elongate and body size increased. Besides the dominance of piscivory, dental morphology and the scarcity of tooth wear reflect accidental dental occlusion that could have been caused by the capturing or seasonal consumption of harder food items. □Basal pterosaurs, heterodonty, dental wear, insectivory, piscivory.
Pinnipeds (seals, sea lions and walruses) are secondarily marine carnivorans that exhibit a wide range of feeding and reproductive specializations. Extant pinnipeds are split into three families: Phocidae (seals), Otariidae (sea lions) and Odobenidae (walruses). Morphometric analyses were used to examine cranial morphology in otariid and phocid pinnipeds. Phocids are more ecologically and taxonomically diverse than otariids, and this study quantitatively assessed the effects of life history, phylogeny and ecology on cranial morphology in these closely related clades of aquatic carnivorans. Fifty-three to 58 three-dimensional landmarks were gathered from 138 specimens, representing 31 of the 33 extant species of otariids and phocids. Principal components analysis was used to identify major axes of variation, and principal component scores were compared with phylogenetic distances and ecological variables to test for significant correlates of skull morphology. Results showed that phocids exhibit a much greater diversity of adult skull morphology than otariids. Shape differences within adult otariids were dominated by males of only one species, Otaria flavescens. In contrast, several species of phocids deviated markedly from the mean phocid morphology. These atypical morphologies were consistently associated with specializations of either feeding or mating strategies. Ontogenetic shape changes are greater, relative to interspecific differences, in otariids than in phocids, and shape dimorphism was observed in only one otariid and two phocid species. Unexpectedly, neither otariids nor phocids showed strong correlations between phylogenetic relationship and cranial morphology. Both clades show strong correlations between cranial shape and some life history and some environmental variables, but phocids show stronger correlations with life-history variables, perhaps reflecting the broad range of reproductive strategies observed in phocids.
Crustaceans have been an important component of marine diversity and biomass since the earliest Phanerozoic. With a relatively well-documented fossil record, they provide an excellent subject for a continuous study of disparity ( bodyplan variety) from the Cambrian to the Recent. A data base of 135 morphological characters forms the basis for cladistic and morphospace studies at the ordinal and sub-ordinal level. Gross cladistic topology is: (Eumalacostraca + Hoplocarida vs Maxillopoda) vs Phyllopoda (paraphyletic). Each of these groups is of approximately equal disparity, and occupies a distinct region of the morphospace plot. A few problematical fossils (e.g. Waptia and Odaraia) fall close to the base of the tree. Comparison of the cladogram with stratigraphic range data indicates the location of probable ghost lineages, and randomization procedures provide a statistical test of the goodness of fit of a given set of stratigraphic ranges to a given tree topology. Disparity indices are calculated at series and stage intervals. Observed range data indicate that Cambrian disparity was approximately one third its present level. The Earliest Ordovician saw a marked decrease, with an increase and subsequent plateau through rest of the period. Increases through the Silurian and Devonian corresponded to the radiation of branchiopods, cephalocarids, and latterly the Eumalacostraca and Hoplocarida. By the end of the Carboniferous, observed disparity had reached over four fifths of Recent levels, and the remaining history of the group saw a gradual but slightly irregular increase up until the end of the Tertiary. Indices of disparity incorporating ghost lineages exhibit less marked peaks and troughs, with fewer perturbations overall. Cladistically-implied disparity in the Lower Cambrian is estimated at three quarters of that in the Recent. Rarefaction is used to compare actual levels of disparity at each time interval with the mean for a similar number of taxa selected randomly from the list of all realized bodyplans. Most intervals preserved a range of forms more disparate than the mean of random samples drawn from the pool of all the taxa considered. From the Triassic to the Recent this difference was intermittently significant. Once occupied, extremes of morphospace tend not to fall vacant again.
A new complete and fully articulated specimen of the anurognathid pterosaur Anurognathus ammoni from the Upper Jurassic Solnhofen Limestone of southern Germany provides new information about the species. The skull is broader than long and quite tall. The naris and antorbital fenestra are both small and anteriorly placed, whereas the orbit is very large. The palatal elements are slender struts of bone separating large openings. The tail is short, but is neither pygostyle-like nor like that of pterodactyloids. The wingfinger, unlike that of almost all pterosaurs, is reduced to three phalanges. Pedal digit V bears two long phalanges. Reexamination of the holotype specimen revealed evidence of bony bumps on the premaxilla and dentary that may have been associated with a fringe of bristles around the mouth. Anurognathus and the other anurognathids were probably adapted to aerial insectivory in low light conditions like extant caprimulgids and insectivorous bats, and may have spent little time on the ground. The taxonomy of the Anurognathidae is reviewed and new diagnoses are presented. A cladistic analysis supports the interpretation that the Anurognathidae is the sister-group to all other pterosaurs.
Two recently collected specimens of the Late Cretaceous pterosaurNyctosaurus differ from all previously known specimens in the possession of a large branching cranial crest. The crest extends upward
and backward from the posterior skull roof and is nearly three times the length of the skull proper. Despite the large crest,
the specimens do not differ significantly in morphology from previously known specimens ofNyctosaurus, and do not seem to represent a new species ofNyctosaurus. The specimens suggest that the cranial crest was developed late in ontogeny, which is consistent with the interpretation
of pterosaur cranial crests as intraspecific display structures.
Zwei neue Exemplare des FlugsauriersNyctosaurus unterscheiden sich von anderen Exemplaren, weil sie einen hohen, abzweigenden Schädelkamm haben. Der Schädelkamm dehnt sich
aufwärts und rückwärts von dem hinteren Schädeldach und ist dreimal so lang wie der Schädel. Trotz des Schädelkamms unterscheiden
sich die neuen Exemplare in der wichtigen Morphologie nicht von anderen Exemplaren. Demnach sind sie keine neue Art. Wahrscheinlich
entwickelte sich der Schädelkamm nur, als das Individuum ein fast ausgewachsenes Tier war. Das stimmt mit der Vermutung überein,
dass der Schädelkamm ein intraspezifisches Zeigmerkmal ist.
Fremdstoffe gelangen als Immissionen und durch gezieltes Einbringen von Agrochemikalien oder die Anwendung von Müllklärschlamm-Komposten
in den Boden. Nennenswerte Negativ-Effekte auf die Bodenmikroorganismen sind im Falle von Pflanzenschutzmitteln nur bei überhöhten,
praxisunüblichen Konzentrationen zu verzeichnen. Im Boden unterliegen die Stoffe vielfältigen Reaktionen, unter denen der
mikrobielle Ab- und Umbau die wirksamste Reaktion zur Selbstreinigung des Bodens von unerwünschten Stoffen (Schadstoffen)
darstellt.
A fundamental contribution of paleobiology to macroevolutionary theory has been the illumination of deep time patterns of diversification. However, recent work has suggested that taxonomic diversity counts taken from the fossil record may be strongly biased by uneven spatiotemporal sampling. Although morphological diversity (disparity) is also frequently used to examine evolutionary radiations, no empirical work has yet addressed how disparity might be affected by uneven fossil record sampling. Here, we use pterosaurs (Mesozoic flying reptiles) as an exemplar group to address this problem. We calculate multiple disparity metrics based upon a comprehensive anatomical dataset including a novel phylogenetic correction for missing data, statistically compare these metrics to four geological sampling proxies, and use multiple regression modeling to assess the importance of uneven sampling and exceptional fossil deposits (Lagerstätten). We find that range-based disparity metrics are strongly affected by uneven fossil record sampling, and should therefore be interpreted cautiously. The robustness of variance-based metrics to sample size and geological sampling suggests that they can be more confidently interpreted as reflecting true biological signals. In addition, our results highlight the problem of high levels of missing data for disparity analyses, indicating a pressing need for more theoretical and empirical work.
Three major arguments have been raised against the crucial claim, documented by Whittington and colleagues for the Burgess Shale fauna, and so contrary to traditional views, that disparity of anatomical design reached an early maximum in the history of multicellular life: (1) the presence of many early taxa with low membership and high rank is an artifact of naming; (2) cladistic analysis of Burgess arthropods negates the claim for greater early disparity; and (3) Whittington's argument is a retrospective fallacy based on assigning high rank to differentia only by virtue of their later capacity to define major branches. I show that all these arguments are either false or illogical, and that the claim for increased early disparity is justified: (1) Taxonomic rank is an artifact, but no one has ever based a claim for greater disparity on this false criterion. (2) Cladistics can only deal with branching order, whereas disparity is a phenetic issue. These two legitimate aspects of evolutionary "relationship" are logically distinct. The rooting of a cladogram only illustrates monophyletic ancestry (which no one doubts, as we are not creationists), and cannot measure disparity. (3) The active stabilization of the differentia of Bauplane (for genetic and developmental reasons only dimly understood) provides a powerful rationale for weighting these characters in considerations of disparity; nothing had so stabilized in the Burgess fauna. If these differentia were steadily changing contingencies, rather than actively stabilized features with "deep" architectural status, then the retrospective argument would be justified. Although the three arguments are wrong, the claim for greater early disparity cannot be confidently established until we develop quantitative techniques for the characterization of morphospace and its differential filling through time. This is a dauntingly difficult problem, much harder than cladistic ordering, but not intractable.
Abstract: The distribution of organic forms is clumpy at any scale from populations to the highest taxonomic categories, and whether considered within clades or within ecosystems. The fossil record provides little support for expectations that the morphological gaps between species or groups of species have increased through time as it might if the gaps were created by extinction of a more homogeneous distribution of morphologies. As the quantitative assessments of morphology have replaced counts of higher taxa as a metric of morphological disparity, numerous studies have demonstrated the rapid construction of morphospace early in evolutionary radiations, and have emphasized the difference between taxonomic measures of morphological diversity and quantitative assessments of disparity. Other studies have evaluated changing patterns of disparity across mass extinctions, ecomorphological patterns and the patterns of convergence within ecological communities, while the development of theoretical morphology has greatly aided efforts to understand why some forms do not occur. A parallel, and until recently, largely separate research effort in evolutionary developmental biology has established that the developmental toolkit underlying the remarkable breadth of metazoan form is largely identical among Bilateria, and many components are shared among all metazoa. Underlying this concern with disparity is a question about temporal variation in the production of morphological innovations, a debate over the relative significance of the generation of new morphologies vs. differential probabilities of their successful introduction, and the relative importance of constraint, convergence and contingency in the evolution of form.
Theropod dinosaurs, an iconic clade of fossil species including Tyrannosaurus and Velociraptor, developed a great diversity of body size, skull form and feeding habits over their 160+ million year evolutionary history. Here, we utilize geometric morphometrics to study broad patterns in theropod skull shape variation and compare the distribution of taxa in cranial morphospace (form) to both phylogeny and quantitative metrics of biting behaviour (function). We find that theropod skulls primarily differ in relative anteroposterior length and snout depth and to a lesser extent in orbit size and depth of the cheek region, and oviraptorosaurs deviate most strongly from the "typical" and ancestral theropod morphologies. Noncarnivorous taxa generally fall out in distinct regions of morphospace and exhibit greater overall disparity than carnivorous taxa, whereas large-bodied carnivores independently converge on the same region of morphospace. The distribution of taxa in morphospace is strongly correlated with phylogeny but only weakly correlated with functional biting behaviour. These results imply that phylogeny, not biting function, was the major determinant of theropod skull shape.
A sexually mature individual of Darwinopterus preserved together with an egg from the Jurassic of China provides direct evidence of gender in pterosaurs and insights into
the reproductive biology of these extinct fliers. This new find and several other examples of Darwinopterus demonstrate that males of this pterosaur had a relatively small pelvis and a large cranial crest, whereas females had a relatively
large pelvis and no crest. The ratio of egg mass to adult mass is relatively low, as in extant reptiles, and is comparable
to values for squamates. A parchment-like eggshell points to burial and significant uptake of water after oviposition. This
evidence for low parental investment contradicts the widespread assumption that reproduction in pterosaurs was like that of
birds and shows that it was essentially like that of reptiles.