Article

Evolutionary shifts in extant mustelid (Mustelidae: Carnivora) cranial shape, body size and body shape coincide with the Mid-Miocene Climate Transition

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Abstract

Environmental changes can lead to evolutionary shifts in phenotypic traits, which in turn facilitate the exploitation of novel adaptive landscapes and lineage diversification. The global cooling, increased aridity and expansion of open grasslands during the past 50 Myr are prime examples of new adaptive landscapes that spurred lineage and ecomorphological diversity of several mammalian lineages such as rodents and large herbivorous megafauna. However, whether these environmental changes facilitated evolutionary shifts in small- to mid-sized predator morphology is unknown. Here, I used a complete cranial and body morphological dataset to examine the timing of evolutionary shifts in cranial shape, body size and body shape within extant mustelids (martens, otters, polecats and weasels) during the climatic and environmental changes of the Cenozoic. I found that evolutionary shifts in all three traits occurred within extant mustelid subclades just after the onset of the Mid-Miocene Climate Transition. These mustelid subclades first shifted towards more elongate body plans followed by concurrent shifts towards smaller body sizes and more robust crania. I hypothesize that these cranial and body morphological shifts enabled mustelids to exploit novel adaptive zones associated with the climatic and environmental changes of the Mid to Late Miocene, which facilitated significant increases in clade carrying capacity.

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... The continuum from body elongation to body robustness is the primary axis of body shape variation within many vertebrate clades (Ward and Mehta 2010;Bergmann and Irschick 2012;Price et al. 2019). Variation in body shape facilitates morphological, functional, and ecological innovations that can lead to increased diversification and/ or niche specialization (Wiens et al. 2006;Collar et al. 2016;Law 2019; Morinaga and Bergmann 2020). For example, extreme body elongation in Australian Lerista lizards enhances fossorial locomotion by enabling elongate species to penetrate sand substrates faster than more robust bodied species (Morinaga and Bergmann 2020). ...
... In addition, carnivorans range in body sizes and shapes from large robust bears to small elongate weasels. Although recent work revealed that smaller carnivorans exhibited more elongate bodies, body size explained only 42% of body shape variation (Law 2021a). This suggests that additional independent factors may influence body size and body shape separately across carnivoran evolution. ...
... This suggests that additional independent factors may influence body size and body shape separately across carnivoran evolution. Furthermore, multiple morphological components contribute to carnivoran body shape variation (Law 2021a); therefore, I also test whether locomotor, hunting, and dietary ecologies influenced the evolution of these underlying morphological components. Because of the different mechanical demands of moving through diverse environments (Kardong 2014), I predict that locomo-tion and hunting behavior will have the greatest influence on the evolution of carnivoran body size and shape as well as on the thoracolumbar region underlying body shape variation. ...
Article
Morphological diversity is often attributed as adaptations to distinct ecologies. Although biologists have long hypothesized that distinct ecologies drive the evolution of body shape, these relationships are rarely tested across macroevolutionary scales in mammals. Here, I tested hypotheses that locomotor, hunting, and dietary ecologies influenced body shape evolution in carnivorans, a morphologically and ecologically diverse clade of mammals. I found that adaptive models with ecological trait regimes were poor predictors of carnivoran body shape and the underlying morphological components that contribute to body shape variation. Instead, the best-supported model exhibited clade-based evolutionary shifts, indicating that the complexity and variation of body shape landscape cannot be effectively captured by a priori ecological regimes. However, ecological adaptations of body shapes cannot be ruled out, as aquatic and terrestrial carnivorans exhibited opposite allometric patterns of body shape that may be driven by different gravitational constraints associated with these different environments. Similar to body size, body shape is a prominent feature of vertebrate morphology that may transcend one-to-one mapping relationships between morphology and ecological traits, enabling species with distinct body shapes to exploit similar resources and exhibit similar ecologies. Together, these results demonstrate that the multidimensionality of both body shape morphology and ecology makes it difficult to disentangle the complex relationship among morphological evolution, ecological diversity, and phylogeny across macroevolutionary scales.
... Las modificaciones craneales y mandibulares entre los clados de Mustelidae están estrechamente relacionadas a la dieta y las estrategias de alimentación (2,33); no obstante, estudios recientes han evidenciado que estas tendencias ecológicas vinculadas a la alimentación se encuentran restringidas fuertemente por la historia evolutiva (52). En este sentido, nuestros análisis morfométricos del cráneo y la ...
... Estas observaciones señalan que los mustelinos y los lutrinos comparten un patrón morfológico craneal similar compuesto por cajas craneanas más anchas y alargadas, rostros más cortos y pequeños y una ubicación más anterior del arco cigomático en comparación con los demás mustélidos, lo cual respalda la existencia de señal filogenética en la morfología craneal del clado Mustelidae como lo indican las pruebas de permutación realizadas. Asimismo, este hallazgo concuerda con Law (2019), quién encontró que durante la Transición Climática del Mioceno Mediohace aproximadamente 14 millones de años-ocurrió dentro de Mustelidae un cambio evolutivo en la forma craneal hacia el clado conformado por Ictonychinae, Mustelinae y Lutrinae, relacionado al ensanchamiento del cráneo y el acortamiento del rostro(52). De esta manera, las similitudes entre los clados hermanos Mustelinae y Lutrinae apoyan la idea sugerida por estudios previos sobre que la transición hacia el estilo de vida acuático en los mustélidos -representado por las nutrias-requirió cambios craneales relativamente simples(2). ...
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La nutria marina, Lontra felina, es un carnívoro generalista con marcadas diferencias en la dieta a lo largo de su distribución en las costas del Pacífico sudeste, pues las poblaciones del norte (Perú) son principalmente piscívoras, mientras que las del sur (Chile) son predominantemente durófagas (e.g. crustáceos). Diferencias alimenticias existen entre especies vivientes de nutrias (Lutrinae) y han sido asociadas a disparidad en las proporciones del cráneo y la mandíbula. Dado que L. felina no ha sido incluida en análisis cuantitativos, se desconoce si su anatomía corresponde con alguno de los ecomorfotipos establecidos para las nutrias –piscívoro o durófago– y si éste presenta variaciones geográficas o sexuales. El objetivo de este estudio fue establecer el ecomorfotipo de alimentación de Lontra felina en un contexto filogenético e investigar su variación morfológica intraespecífica. Utilizando morfometría geométrica, se cuantificó la morfología craneal y mandibular de especímenes de Lontra felina de Perú y Chile y otras 15 especies de mustélidos. La comparación interespecífica se realizó mediante análisis de componentes principales con mapeo filogenético y las variaciones intraespecíficas se evaluaron usando análisis discriminantes y pruebas de t. Los análisis morfométricos demostraron que la nutria marina presenta un ecomorfotipo alimenticio mixto, con características tanto del piscívoro (cráneos más alargados, planos y estrechos, mandíbulas más alargadas y procesos angulares más grandes) como del durófago (cráneos más cortos, convexos y anchos, áreas molariformes más grandes y mandíbulas más cortas). Los análisis intraespecíficos indicaron la ausencia de dimorfismo sexual, pero revelaron diferencias geográficas en la forma asociadas a la variación latitudinal en la dieta entre Perú y Chile. Así, las poblaciones de Perú exhibieron cráneos más alargados y estrechos, propios del ecomorfotipo piscívoro, y, las de Chile, cráneos más cortos y anchos, típicos del ecomorfotipo durófago. Considerando las diferencias genéticas previamente reportadas, nuestros resultados apoyan la existencia de un proceso de especiación alopátrica en marcha conducido por la dieta y cuyo conocimiento es de relevancia para su conservación.
... Weasels and polecats have been qualitatively described as elongate for centuries (Shaw 1800;Griffith 1827;Gray 1865;Brown and Lasiewski 1972;Gliwicz 1988;King 1989). These descriptions were confirmed with quantitative data, which showed that mustelid body elongation may have facilitated increased species richness (Law et al. 2018bLaw 2019). However, mustelids are not the only terrestrial carnivorans to be qualitatively described as elongate. ...
... In contrast, the ancestral nodes of Mustelinae and Prionodontidae originated within the nonelongate region of morphospace, and their respective descendants extended towards the lower bound of pPC 1 to occupy their own region of morphospace (Fig. 2). For musteline weasels, this evolutionary trajectory fits the working hypothesis that axial elongation serves as an innovation that enabled weasels and other mustelids to pursue subterranean prey with more flexible bodies for greater locomotor efficiency (Law et al. 2018bLaw 2019). Gulonines (martens) and ictonychines (polecats) also fit within this hypothesis as they also approach the lower bound of pPC 1 and pursue prey in underground or snow burrows. ...
Article
Although convergence is often recognized as a ubiquitous feature across the Tree of Life, whether the underlying traits also exhibit similar evolutionary pathways towards convergent forms puzzles biologists. In carnivoran mammals, “elongate,” “slender,” and “long” are often used to describe and even to categorize mustelids (martens, polecats, and weasels), herpestids (mongooses), viverrids (civets and genets), and other carnivorans together. But just how similar these carnivorans are and whether there is convergence in the morphological component that contribute to elongation has never been assessed. Here, I found that these qualitatively-described elongate carnivorans exhibited incomplete convergence towards elongate bodies compared to other terrestrial carnivorans. In contrast, the morphological components underlying body shape variation do not exhibit convergence despite evidence that these components are more elongate in elongate carnivorans compared to non-elongate carnivorans. Furthermore, these components also exhibited shorter but different phylogenetic half-lives towards more elongate adaptive peaks, indicating that different selective pressures can create multiple pathways to elongation. Incorporating the fossil record will facilitate further investigation of whether body elongation evolved adaptively or if it is simply a retained ancestral trait.
... Recent work on musteloid trait diversification also suggests that multiple evolutionary processes underlie the mustelid body plan. Law et al. (2019) found that the clade composed of the Helictidinae, Ictonychinae, Guloninae, Mustelinae and Lutrinae ( Fig. 1) underwent an evolutionary transition towards a more elongate body, albeit more likely due to a multi-rate BM process, and Law (2019) found that the subclade of the Ictonychinae, Mustelinae and Lutrinae experienced shifts in selective regime in cranial robustness and body size compared to other musteloids. Law et al. (2019) also found that fore-and hindlimb length likely evolved according a multi-rate BM process that distinguishes between a clade of shorter limbed mustelids (Ictonychinae, Mustelinae and Lutrinae) and other mustelids. ...
... However, body elongation in mustelids was found to be associated with shortening of the forelimb only and not the hindlimb. The results of Law et al. (2018Law et al. ( , 2019 and Law (2019) Looking at parameter estimates for the best fitting models reveals wide confidence limits (Supporting Information, Tables S2, S3), as was found when fitting diversification models to mustelid forelimb morphology (Kilbourne, 2017). Though the confidence limits for phenotypic optima of some best fitting models do not overlap (e.g. ...
Article
Though form-function relationships of the mammalian locomotor system have been investigated for over a century, recent models of trait evolution have hitherto been seldom used to identify likely evolutionary processes underlying the locomotor system’s morphological diversity. Using mustelids, an ecologically diverse carnivoran lineage, I investigated whether variation in hindlimb skeletal morphology functionally coincides with climbing, digging, swimming and generalized locomotor habits by using 15 linear traits of the femur, tibia, fibula, calcaneum and metatarsal III across 44 species in a principal component analysis. I subsequently fit different models of Brownian motion and adaptive trait diversification individually to each trait. Climbing, digging and swimming mustelids occupy distinct regions of phenotypic space characterized by differences in bone robustness. Models of adaptive and neutral evolution are, respectively, the best fits for long bone lengths and muscle in-levers, suggesting that different kinds of traits may be associated with different evolutionary processes. However, simulations based upon models of best fit reveal low statistical power to rank the models. Though differences in mustelid hindlimb skeletal morphology appear to coincide with locomotor habits, further study, with sampling expanded beyond the Mustelidae, is necessary to better understand to what degree adaptive evolution shapes morphological diversity of the locomotor system.
... Recent work, however, demonstrated that quantifying body shape variation can reveal patterns of diversification in some mammalian clades. For example, mustelids were found to exhibit significant evolutionary shifts towards smaller, more elongate bodies with reduced limb lengths that in turn led to their increased species richness (Law et al. 2018b;Law et al. 2019;Law 2019). Therefore, whether these evolutionary patterns in body plans are unique to musteloids or occur in broader clades of mammals is unknown because of the lack of mammalian body shape datasets. ...
... which may be unsurprising considering they are the most ecomorphologically disparate carnivoran family; members range from insectivorous, fossorial badgers to hypercarnivorous, cursorial weasels to piscivorous, aquatic otters(Law et al. 2018a;Fabre et al. 2015;Kitchener et al. 2018;Parsi-Pour and Kilbourne 2020). Mustelidae also includes the most elongate carnivorans, weasels, and polecatsLaw 2019). Interestingly, Results of the PGLS regressions of body size versus body shape across Carnivora and within carnivoran clades. ...
Article
The diversity of body shapes is one of the most prominent features of phenotypic variation in vertebrates. Biologists, however, still lack a full understanding of the underlying morphological components that contribute to its diversity, particularly in endothermic vertebrates such as mammals. In this study, I tested hypotheses pertaining to the evolution of the cranial and axial components that contribute to the diversity of carnivoran body shapes. I found three trends in the evolution of carnivoran body shapes: 1) carnivorans exhibit diverse body shapes with intrafamilial variation predicted best by family clade age, 2) body shape is driven by strong allometric effects of body size where species become more elongate with decreasing size, and 3) the thoracic and lumbar regions and rib length contribute the most to body shape variation, albeit pathways differ between different families. These results reveal the morphological patterns that led to increased diversity in carnivoran body shapes and provide elucidate the similarities and dissimilarities that govern body shape diversity across vertebrates. This article is protected by copyright. All rights reserved
... Combining three-dimensional comparative morphology and phylogenetic comparative methods, this study represents a novel approach to understand the correspondence between the evolutionary pathways shaping the humeral variation, by decomposing its biomechanical and morphological components. Our results showed a strong link between phenotypic variation and ecological differences between taxa at a macroevolutionary scale, Pimiento et al. 2019;Stanchak et al. 2019). However, we also found a marked decoupling between the processes affecting the evolution of humeral morphological and biomechanical disparity, where diet and size were highly associated with differences in shape and biomechanics, respectively. ...
... Novel modelling techniques (independent of a priori assumptions) to estimate otherwise unexplored evolutionary shifts further inform the mode and tempo of phenotypic evolution of the humerus in bats. Evolutionary shifts in shape and biomechanics could have relaxed ecological pressures constraining diversification, leading to the evolution of novel dietary- foraging strategies and large body size(Law 2019), between geographically isolated taxa (López-Aguirre et al. 2018). The distribution of evolutionary shifts found in the proximal diaphysis shows adaptive shifts towards higher J (i.e. ...
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Bats use their forelimbs in different ways, flight being the most notable example of morphological adaptation. However, different behavioural specializations beyond flight have also been described in several bat lineages. Understanding the postcranial evolution during the locomotory and behavioural diversification of bats is fundamental to understanding bat evolution. We investigate whether different functional demands influenced the evolutionary trajectories of humeral cross-sectional shape and biomechanics. We found a strong ecological signal and no phylogenetic structuring in the morphological and biomechanical variation in humerus phenotypes. Decoupled modes of shape and biomechanical variation were consistently found, with size and diet explaining variation in shape and biomechanics respectively. We tested both hypothesis- and data-driven multivariate evolutionary models, revealing decoupled pathways of evolution across different sections of the humerus diaphysis. We found evidence for a complex evolutionary landscape where flight might have acted as an evolutionary constraint, while size- and diet-based ecological opportunities facilitated diversification. We also found shifts in adaptive regimes independent from the evolution of flight (i.e. terrestrial locomotion and upstand roosting). Our results suggest that complex and multiple evolutionary pathways interplay in the postcranium, leading to the independent evolution of different features and regions of skeletal elements optimised for different functional demands.
... Recent work on musteloid trait diversification also suggests that multiple evolutionary processes underlie the mustelid body plan. Law et al. (2019) found that the clade composed of the Helictidinae, Ictonychinae, Guloninae, Mustelinae and Lutrinae ( Fig. 1) underwent an evolutionary transition towards a more elongate body, albeit more likely due to a multi-rate BM process, and Law (2019) found that the subclade of the Ictonychinae, Mustelinae and Lutrinae experienced shifts in selective regime in cranial robustness and body size compared to other musteloids. Law et al. (2019) also found that fore-and hindlimb length likely evolved according a multi-rate BM process that distinguishes between a clade of shorter limbed mustelids (Ictonychinae, Mustelinae and Lutrinae) and other mustelids. ...
... However, body elongation in mustelids was found to be associated with shortening of the forelimb only and not the hindlimb. The results of Law et al. (2018Law et al. ( , 2019 and Law (2019) Looking at parameter estimates for the best fitting models reveals wide confidence limits (Supporting Information, Tables S2, S3), as was found when fitting diversification models to mustelid forelimb morphology (Kilbourne, 2017). Though the confidence limits for phenotypic optima of some best fitting models do not overlap (e.g. ...
Article
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Background Morphological diversity of limb bone lengths, diameters, and proportions in mammals is known to vary strongly with locomotor habit. It remains less well known how different locomotor habits are correlated with cross-sectional traits of the limb skeleton, such as cross-sectional area (CSA), second moments of area (SMA), and section modulus (MOD) and whether these traits have evolved adaptively. CSA and SMA represent the bone’s resistance to axial compression and bending, respectively, whereas MOD represents bone structural strength related to shape. Sampling 28 species of mustelids, a carnivoran lineage with diverse locomotor habits, we tested for differences in humeral, radial, and ulnar cross-sectional traits among specialists for climbing, digging, and swimming, in addition to generalists. Given that the limbs of digging specialists function in the dense substance of soil, and that swimming specialists need to counteract buoyancy, we predicted that these mustelids with these specializations should have the greatest values of cross-sectional traits. Results We analyzed cross-sectional traits (calculated via μCT scanning and rendered dimensionless) in 5% increments along a bone’s length and found significant differences among locomotor habits, though differences in ulnar cross-sectional traits were fewer than those for the humerus and radius. Swimming specialists had the greatest values of cross-sectional traits, followed by digging specialists. Climbing specialists had the lowest values of cross-sectional traits. However, phylogenetic affinity underlies these results. Fitting models of trait evolution to CSA and SMA revealed that a multi-rate Brownian motion model and a multi-optima Ornstein-Uhlenbeck model are the best-fitting models of evolution for these traits. However, inspection of α-values uncovered that many of the OU models did not differ from a Brownian motion model. Conclusions Within Mustelidae, differences in limb function and locomotor habit influence cross-sectional traits in ways that produce patterns that may diverge from adaptive patterns exhibited by external traits (e.g., bone lengths) of the mammalian limb skeleton. These results suggest that not all the traits of a single organ evolve under a single evolutionary process and that models of trait evolution should be fit to a range of traits for a better understanding of the evolution of the mammalian locomotor system. Electronic supplementary material The online version of this article (10.1186/s12862-019-1349-8) contains supplementary material, which is available to authorized users.
... There was an arid belt that existed from the western-most part to the eastern coasts, and arid and semi-arid conditions dominated in large areas of China [63]. This led to the formation of temperate grasslands and savannah ecosystems on most land at the expense of forest decline [61,62,64]. Such ecosystem transformations might have acted as a driving force that promoted the rapid diversification of micronetines (clade A) and erigonines (clade B) but might be a major constraint on the survival of Solenysa species. ...
Article
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A time scale of phylogenetic relationships contributes to a better understanding of the evolutionary history of organisms. Herein, we investigate the temporal divergence pattern that gave rise to the poor species diversity of the spider genus Solenysa in contrast with the other six major clades within linyphiids. We reconstructed a dated phylogeny of linyphiids based on multi-locus sequence data. We found that Solenysa diverged from other linyphiids early in the Cretaceous (79.29 mya), while its further diversification has been delayed until the middle Oligocene (28.62 mya). Its diversification trend is different from all of the other major lineages of linyphiids but is closely related to the Cenozoic ecosystem transition caused by global climate changes. Our results suggest that Solenysa is a Cretaceous relict group, which survived the mass extinction around the K-T boundary. Its low species diversity, extremely asymmetric with its sister group, is largely an evolutionary legacy of such a relict history, a long-time lag in its early evolutionary history that delayed its diversification. The limited distribution of Solenysa species might be related to their extreme dependence on highly humid environments.
... Clearly, the elongation in body length in snakes is not accompanied by a corresponding elongation of the intestine, even though other organs, such as the stomach, the kidneys, lungs or spleen clearly appear elongated when compared to other reptiles [73]. This contrasts with the mustelids-a group of mammalian carnivores that also evolved an elongated body shape [74]. At comparable body mass, mustelids have longer intestines than other carnivores [75], mirroring a comparison of body mass and body length [76]. ...
Article
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Although relationships between intestinal morphology between trophic groups in reptiles are widely assumed and represent a cornerstone of ecomorphological narratives, few comparative approaches actually tested this hypothesis on a larger scale. We collected data on lengths of intestinal sections of 205 reptile species for which either body mass (BM), snout-vent-length (SVL) or carapax length (CL) was recorded, transforming SVL or CL into BM if the latter was not given, and analyzed scaling patterns with BM and SVL, accounting for phylogeny, comparing three trophic guilds (faunivores, omnivores, herbivores), and comparing with a mammal dataset. Length-BM relationships in reptiles were stronger for the small than the large intestine, suggesting that for the latter, additional factors might be relevant. Adding trophic level did not consistently improve model fit; only when controlling for phylogeny, models indicated a longer large intestine in herbivores, due to a corresponding pattern in lizards. Trophic level effects were highly susceptible to sample sizes, and not considered strong. Models that linked BM to intestine length had better support than models using SVL, due to the deviating body shape of snakes. At comparable BM, reptiles had shorter intestines than mammals. While the latter finding corresponds to findings of lower tissue masses for the digestive tract and other organs in reptiles as well as our understanding of differences in energetic requirements between the classes, they raise the hitherto unanswered question what it is that reptiles of similar BM have more than mammals. A lesser effect of trophic level on intestine lengths in reptiles compared to mammals may stem from lesser selective pressures on differentiation between trophic guilds, related to the generally lower food intake and different movement patterns of reptiles, which may not similarly escalate evolutionary arms races tuned to optimal agility as between mammalian predators and prey.
... Our PLM results revealed a significant effect of evolutionary history and ecology on humeral shape at the three levels studied (i.e. whole-bone, diaphyseal and epiphyseal), a result expected following studies of morphological variation in bats Brokaw & Smotherman, 2020;Monteiro & Nogueira, 2011;Rossoni et al., 2017), other mammals (Law, 2019) and other vertebrates (Gill et al., 2014;Hedrick et al., 2020;Vidal-García & Keogh, 2017;Wilson, 2013). Morphological adaptations of the humerus and shoulder joint in bats have proven informative, providing insight into the functional performance of bat species and the systematic arrangement of the order (Gaudioso et al., 2020;Hand et al., 2009;Schlosser-Sturm & Schliemann, 1995). ...
Article
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Bats show a remarkable ecological diversity that is reflected both in dietary and foraging guilds (FGs). Cranial ecomorphological adaptations linked to diet have been widely studied in bats, using a variety of anatomical, computational and mathematical approaches. However, foraging‐related ecomorphological adaptations and the concordance between cranial and postcranial morphological adaptations remain unexamined in bats and limited to the interpretation of traditional aerodynamic properties of the wing (e.g. wing loading [WL] and aspect ratio [AR]). For this reason, the postcranial ecomorphological diversity in bats and its drivers remain understudied. Using 3D virtual modelling and geometric morphometrics (GMM), we explored the phylogenetic, ecological and biological drivers of humeral morphology in bats, evaluating the presence and magnitude of modularity and integration. To explore decoupled patterns of variation across the bone, we analysed whole‐bone shape, diaphyseal and epiphyseal shape. We also tested whether traditional aerodynamic wing traits correlate with humeral shape. By studying 37 species from 20 families (covering all FGs and 85% of dietary guilds), we found similar patterns of variation in whole‐bone and diaphyseal shape and unique variation patterns in epiphyseal shape. Phylogeny, diet and FG significantly correlated with shape variation at all levels, whereas size only had a significant effect on epiphyseal morphology. We found a significant phylogenetic signal in all levels of humeral shape. Epiphyseal shape significantly correlated with wing AR. Statistical support for a diaphyseal‐epiphyseal modular partition of the humerus suggests a functional partition of shape variability. Our study is the first to show within‐structure modular morphological variation in the appendicular skeleton of any living tetrapod. Our results suggest that diaphyseal shape correlates more with phylogeny, whereas epiphyseal shape correlates with diet and FG.
... The fact that the relative body length was influenced by phylogeny was in part expected because the same finding has been recently reported in mustelids, a family of carnivorans, with some taxa exhibiting highly elongated bodies , Law, 2019. The morphological regions of the lumbosacral, sacrocaudal and sacroiliac articulations are also highly variable among species. ...
Article
The sacrum is a key piece of the vertebrate skeleton, since it connects the caudal region with the presacral region of the vertebral column and the hind limbs through the pelvis. Therefore, understanding its form and function is of great relevance in vertebrate ecomorphology. However, it is striking that morphometric studies that quantify its morphological evolution in relation to function are scarce. The main goal of this study is to investigate the morphological evolution of the sacrum in relation to its function in the mammalian order Carnivora, using three‐dimensional (3D) geometric morphometrics. Principal component analysis under a phylogenetic background indicated that changes in sacrum morphology are mainly focused on the joint areas where it articulates with other parts of the skeleton allowing resistance to stress at these joints caused by increasing muscle loadings. In addition, we demonstrated that sacrum morphology is related to both the length of the tail relativised to the length of the body, and the length of the body relativised to body mass. We conclude that the sacrum in carnivores has evolved in response to the locomotor requirements of the species analysed, but in locomotion, each family has followed alternative morphological solutions to address the same functional demands. The sacrum in carnivores has evolved in response to the locomotor requirements of the species analysed, but in locomotion, each family has followed alternative morphological solutions to address the same functional demands.
... Skull evolution has been poorly studied using contemporary methods in anurans (frogs and toads) relative to more speciespoor lineages [e.g., carnivoran mammals (1,16) and crocodilians (17,18)]. Frog skulls may be understudied because it has been assumed that the highly derived Bauplan and skeletal morphology of this clade are tightly conserved (19). ...
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Frogs (Anura) are one of the most diverse vertebrate orders, comprising more than 7,000 species with a worldwide distribution and extensive ecological diversity. In contrast to other tetrapods, frogs have a highly derived body plan and simplified skull. In many lineages of anurans, increased mineralization has led to hyperossified skulls, but the function of this trait and its relationship with other aspects of head morphology are largely unexplored. Using three-dimensional morphological data from 158 species representing all frog families, we assessed wide-scale patterns of shape variation across all major lineages, reconstructed the evolutionary history of cranial hyperossification across the anuran phylogeny, and tested for relationships between ecology, skull shape, and hyperossification. Although many frogs share a conserved skull shape, several extreme forms have repeatedly evolved that commonly are associated with hyperossification, which has evolved independently more than 25 times. Variation in cranial shape is not explained by phylogenetic relatedness but is correlated with shifts in body size and ecology. The species with highly divergent, hyperossified skulls often have a specialized diet or a unique predator defense mechanism. Thus, the evolution of hyperossification has repeatedly facilitated the expansion of the head into multiple new shapes and functions.
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Τhe functional morphology of the skull of the fossil badger Meles dimitrius from the Early Pleistocene of Greece is studied by means of comparative myological and osteological analyses with the extant representatives of the genus Meles from Europe and Asia. The myological analysis of the masticatory system allowed the reconstruction of a ‘muscle map’ of the significant muscles for feeding and prey capture for the extant Meles meles and, by analogy, for the extinct Meles dimitrius. The quantitative osteological analysis computed several functional cranial, mandibular, and dental measurements and indices, as well as endocranial volume, bite force, and body mass, in order to identify characters that could be attributed to different ecomorphs. Two main ecomorphological groups were recognized within extant Meles. One includes the mainland forms (M. meles, M. leucurus) and the other the insular populations (M. canescens from Crete and M. anakuma from Japan). Apart from its size, Meles dimitrius appears closer to the insular group, which is characterized by a relatively more developed masticatory system, a well-developed temporalis muscle, increased bite forces, increased endocranial volume and possibly a better adaptation to processing meat. The similarity of M. dimitrius with the insular group could be related to the retention of a primitive active predatory and meat-consuming behavior. Alternatively, M. dimitrius could have represented a relatively isolated population having evolved features convergently found in the insular extant badgers.
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Divergence along the benthic-pelagic axis is one of the most widespread and repeated patterns of morphological variation in fishes, producing body shape diversity associated with ecology and swimming mechanics. This ecological shift is also the first stage of the explosive adaptive radiation of cichlid fishes in the East African Rift Lakes. We use two hybrid crosses of cichlids (Metriaclima sp. x Aulonocara sp. and Labidochromis sp. x Labeotropheus sp., >975 animals total) along the benthic-pelagic ecomorphological axis to determine the genetic basis of body shape diversification. Using a series of both linear and geometric shape measurements, we identify 55 quantitative trait loci (QTL) that underlie various aspects of body shape variation associated with benthic-pelagic divergence. These QTL are spread throughout the genome, each explain 3.0-7.2% of phenotypic variation, and are largely modular. Further, QTL are distinct both between these two crosses of Lake Malawi cichlids and compared to previously identified QTL for body shape in fishes such as sticklebacks. We find that body shape is controlled by many genes of small effects. In all, we find that convergent benthic and pelagic body phenotypes commonly observed across fish clades are most likely due to distinct genetic and molecular mechanisms.
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Carnivorans represent extreme ecomorphological diversity, encompassing remarkable variation in form, habitat, and diet. The relationship between the masticatory musculature and dietary ecology has been explored in a number of carnivoran lineages, including felids and the superfamily Musteloidea. In this study, we present novel architectural data on two additional carnivoran families – Ursidae and Canidae – and supplement these previous studies with additional felid, musteloid, herpestid, hyaenid, and viverrid taxa (a total of 53 species across 10 families). Gross dissection data were collected following a standardized protocol ‐ sharp dissection followed by chemical digestion. Summed jaw adductor forces were also transformed into bite force estimates (BF) using osteologically‐calculated leverages. All data were linearized, log‐transformed, and size‐adjusted using two proxies for each taxon – body mass and cranial geometric mean – to assess relative scaling trends. These architectural data were then analyzed in the context of dietary ecology to examine the impact of dietary size and dietary mechanical properties. Muscle mass, physiological cross‐sectional area and BF scaled with isometry or positive allometry in all cases, whereas fascicle lengths scaled with isometry or negative allometry. With respect to diet, body mass adjusted fascicle lengths were strongly correlated with dietary size in musteloids, but not in any other lineage. The relationship between size‐adjusted BF and dietary mechanical properties was also significant within musteloids, and across the sample as a whole, but not within other individual lineages. This interfamilial trend may reflect the increased morphological and dietary diversity of musteloids relative to other carnivoran groups. This article is protected by copyright. All rights reserved.
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Pleistocene glacial cycles are thought to have driven ecological niche shifts, including novel niche formation. North American pine martens, Martes americana and M. caurina, are exemplar taxa thought to have diverged molecularly and morphologically during Pleistocene glaciation. Previous research found correlations between Martes limb morphology with biome and climate, suggesting that appendicular evolution may have occurred via adaptation to selective pressures imposed by novel and shifting habitats. Such variation can also be achieved through non-adaptive means such as genetic drift. Here, we evaluate whether regional genetic differences reflect limb morphology differences among populations of M. americana and M. caurina by analyzing evolutionary tempo and mode of six limb elements. Our comparative phylogenetic models indicate that genetic structure predicts limb shape better than size. Marten limb size has low phylogenetic signal, and the best supported model of evolution is punctuational (kappa), with morphological and genetic divergence occurring simultaneously. Disparity through time analysis suggests that the tempo of limb evolution in Martes tracks Pleistocene glacial cycles, such that limb size may be responding to shifting climates rather than population genetic structure. Contrarily, we find that limb shape is strongly tied to genetic relationships, with high phylogenetic signal and a lambda mode of evolution. Overall, this pattern of limb size and shape variation may be the result of geographic isolation during Pleistocene glacial advance, while declines in disparity suggest hybridization during interglacial periods. Future inclusion of extinct populations of Martes, which were more morphologically and ecologically diverse, may further clarify Martes phenotypic evolution.
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Size and shape are often considered important variables that lead to variation in performance. In studies of feeding, size‐corrected metrics of the skull are often used as proxies of biting performance; however, few studies have examined the relationship between cranial shape in it's entirety and estimated bite force across species and how dietary ecologies may affect these variables differently. Here, we used geometric morphometric and phylogenetic comparative approaches to examine relationships between cranial morphology and estimated bite force in the carnivoran clade Musteloidea. We found a strong relationship between cranial size and estimated bite force but did not find a significant relationship between cranial shape and size‐corrected estimated bite force. Many‐to‐one mapping of form to function may explain this pattern because a variety of evolutionary shape changes rather than a single shape change may have contributed to an increase in relative biting ability. We also found that dietary ecologies influenced cranial shape evolution but did not influence cranial size nor size‐corrected bite force evolution. While musteloids with different diets exhibit variation in cranial shapes, they have similar estimated bite forces suggesting that other feeding performance metrics and potentially non‐feeding traits are also important contributors to cranial evolution. We postulate that axial and appendicular adaptations and the interesting feeding behaviors reported for species within this group also facilitate different dietary ecologies between species. Future work integrating cranial, axial, and appendicular form and function with behavioral observations will reveal further insights in the evolution of dietary ecologies and other ecological variables. This article is protected by copyright. All rights reserved.
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At 50 kg in estimated weight, the extinct Siamogale melilutra is larger than all living otters, and ranks among the largest fossil otters. The biomechanical capability of S. melilutra jaws as related to their large size is unknown but crucial to reconstructing the species’ potentially unique ecological niche. Here we compare the mandibular biomechanics of S. melilutra using engineering-based performance measures against ten extant otter biomechanical models. Despite a wide range of feeding preferences from durophagy to piscivory, living otter species exhibit a linear relationship between mandible stiffness and volume, as expected in isometric model scaling. In contrast, S. melilutra models exhibit a six-fold increase in stiffness from expected stiffness-volume relationships calculated from extant species models. Unlike stiffness, mechanical efficiency of biting is conserved among living otters and in S. melilutra. These findings indicate that although similar to living bunodont otters in morphology and biting efficiency, jaw strength in S. melilutra far surpasses molluscivores such as sea otters and Cape clawless otters, even after accounting for size. Therefore, Siamogale represents a feeding ecomorphology with no living analog, and its giant size and high mandibular strength confer shell-crushing capability matched only by other extinct molluscivores such as the marine bear Kolponomos.
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Adaptive radiation is hypothesized to be a primary mechanism that drives the remarkable species diversity and morphological disparity across the Tree of Life. Tests for adaptive radiation in extant taxa are traditionally estimated from calibrated molecular phylogenies with little input from extinct taxa. With 85 putative species in 33 genera and over 400 described extinct species, the carnivoran superfamily Musteloidea is a prime candidate to investigate patterns of adaptive radiation using both extant- and fossil-based macroevolutionary methods. The species diversity and equally impressive ecological and phenotypic diversity found across Musteloidea is often attributed to 2 adaptive radiations coinciding with 2 major climate events, the Eocene-Oligocene transition and the Mid-Miocene Climate Transition. Here, we compiled a novel time-scaled phylogeny for 88% of extant musteloids and used it as a framework for testing the predictions of adaptive radiation hypotheses with respect to rates of lineage diversification and phenotypic evolution. Contrary to expectations, we found no evidence for rapid bursts of lineage diversification at the origin of Musteloidea, and further analyses of lineage diversification rates using molecular and fossil-based methods did not find associations between rates of lineage diversification and the Eocene-Oligocene transition or Mid-Miocene Climate Transition as previously hypothesized. Rather, we found support for decoupled diversification dynamics driven by increased clade carrying capacity in the branches leading to a subclade of elongate mustelids. Supporting decoupled diversification dynamics between the subclade of elongate mustelids and the ancestral musteloid regime is our finding of increased rates of body length evolution, but not body mass evolution, within the decoupled mustelid subclade. The lack of correspondence in rates of body mass and length evolution suggest that phenotypic evolutionary rates under a single morphological metric, even one as influential as mass, may not capture the evolution of diversity in clades that exhibit elongate body shapes. The discordance in evolutionary rates between body length and body mass along with evidence of decoupled diversification dynamics suggests that body elongation might be an innovation for the exploitation of novel Mid-Miocene resources, resulting in the radiation of some musteloids.
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We describe cranial and mandibular remains of three undescribed individuals of the giant mustelid Megalictis ferox Matthew, 1907 from the latest Arikareean (Ar4), Early Miocene mammal fauna of Nebraska, and Wyoming (USA) housed at the American Museum of Natural History (New York, USA). Our phylogenetic hypothesis indicates that Ar4 specimens assigned to M. ferox constitute a monophyletic group. We assign three additional species previously referred to Paroligobunis to Megalictis: M. simplicidens, M. frazieri, and “M.” petersoni. The node containing these four species of Megalictis and Oligobunis forms the Oligobuninae. We test the hypothesis that Oligobuninae (Megalictis and Oligobunis) is a stem mustelid taxon. Our results indicate that the Oligobuninae form the sister clade to the crown extant mustelids. Based on the cranium, M. ferox is a jaguar-size mustelid and the largest terrestrial mustelid known to have existed. This new material also sheds light on a new ecomorphological interpretation of M. ferox as a bone-crushing durophage (similar to hyenas), rather than a cat-like hypercarnivore, as had been previously described. The relative large size of M. ferox, together with a stout rostrum and mandible made it one of the more powerful predators of the Early Miocene of the Great Plains of North America.
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A major goal of evolutionary studies is to better understand how complex morphologies are related to the different functions and behaviours in which they are involved. For example, during locomotion and hunting behaviour, the head and the eyes have to stay at an appropriate level in order to reliably judge distance as well as to provide postural information. The morphology and orientation of the orbits and cranial base will have an impact on eye orientation. Consequently, variation in orbital and cranial base morphology is expected to be correlated with aspects of an animal's lifestyle. In this study, we investigate whether the shape of the skull evolves in response to the functional demands imposed by ecology and behaviour using geometric morphometric methods. We test if locomotor habitats, diet, and activity pattern influence the shape of the skull in musteloid carnivorans using (M)ANOVAs and phylogenetic (M)ANOVAs, and explore the functional correlates of morphological features in relation to locomotor habitats, diet, and activity pattern. Our results show that phylogeny, locomotion and, diet strongly influence the shape of the skull, whereas the activity pattern seems to have a weakest influence. We also show that the locomotor environment is highly integrated with foraging and feeding, which can lead to similar selective pressures and drive the evolution of skull shape in the same direction. Finally, we show similar responses to functional demands in musteloids, a super family of close related species, as are typically observed across all mammals suggesting the pervasiveness of these functional demands.
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The spread of open grassy habitats and the evolution of long-legged herbivorous mammals with high-crowned cheek teeth have been viewed as an example of coevolution. Previous studies indicate that specialized predatory techniques in carnivores do not correlate with the spread of open habitats in North America. Here we analyse new data on elbow-joint shape for North American canids over the past ∼37 million years and show that incipiently specialized species first appeared along with the initial spread of open habitats in the late Oligocene. Elbow-joint morphologies indicative of the behavior of modern pounce-pursuit predators emerged by the late Miocene coincident with a shift in plant communities from C3 to C4 grasses. Finally, pursuit canids first emerged during the Pleistocene. Our results indicate that climate change and its impact on vegetation and habitat structure can be critical for the emergence of ecological innovations and can alter the direction of lineage evolution.
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The weasels (Mustela spp.) are a group of small mustelid carnivores that originated in the late Pliocene and are now distributed throughout the Holarctic region. Mustela erminea, the stoat or ermine, is circumboreal north of about 40°N. M. nivalis is sympatric with erminea over most of the same area. It includes two distinct subspecies, the common weasel of western Europe and Britain (M. n. vulgaris Erxleben 1777), and the least weasel of northern Scandinavia, USSR, and North America (M. n. nivalis Linnaeus 1766), which are different in appearance and range (Stolt 1979) but interbreed in captivity (F. Frank, pers. comm.). A third species, M. frenata, the long-tailed weasel, is confined to America, from about 50°N to about 15°S.
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A long-standing hypothesis in adaptive radiation theory is that ecological opportunity constrains rates of phenotypic evolution, generating a burst of morphological disparity early in clade history. Empirical support for the early burst model is rare in comparative data, however. One possible reason for this lack of support is that most phylogenetic tests have focused on extant clades, neglecting information from fossil taxa. Here, I test for the expected signature of adaptive radiation using the outstanding 40-My fossil record of North American canids. Models implying time- and diversity-dependent rates of morphological evolution are strongly rejected for two ecologically important traits, body size and grinding area of the molar teeth. Instead, Ornstein-Uhlenbeck processes implying repeated, and sometimes rapid, attraction to distinct dietary adaptive peaks receive substantial support. Diversity-dependent rates of morphological evolution seem uncommon in clades, such as canids, that exhibit a pattern of replicated adaptive radiation. Instead, these clades might best be thought of as deterministic radiations in constrained Simpsonian subzones of a major adaptive zone. Support for adaptive peak models may be diagnostic of subzonal radiations. It remains to be seen whether early burst or ecological opportunity models can explain broader adaptive radiations, such as the evolution of higher taxa.
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The alternating mountain ranges and desert basins of the Great Basin in the western United States support higher species diversity of mammals than any other region of comparable area in temperate North America. Topographically complex regions have strong environmental gradients and heterogeneous habitats that result in fragmented geographic ranges over long periods and may promote speciation. In order to evaluate the influence of topography and climate on mammal diversification, we traced the history of mammal diversity during the formation of basin-and-range topography. We compiled species-occurrence data from the NeoMap database of fossil mammals and calculated standing diversity, origination rate, extinction rate, diversification rate (originations � extinctions), and turnover rate (originations þ extinctions) for million-year intervals. We evaluated changes in faunal composition (species in mammalian orders and species in rodent families) over time and assessed whether significant changes in diversity and faunal composition tracked major changes in landscape history. Neogene geologic evolution generated by tectonic activity and changing climate created the topographic complexity and habitat heterogeneity of the Great Basin. Over the last 30 million years, extensional tectonic processes caused an older high plateau to collapse and stretch from east to west, resulting in longitudinal expansion by ~235 km to form the Great Basin. Average elevation decreased by 1–3 km. Global warming and associated increases in regional precipitation from 17 to 14 million years ago (mya; the Miocene Climatic Optimum [MCO]) interrupted the long-term trend of Cenozoic cooling and aridification. From 30 to 2 mya, Great Basin mammal diversity peaked during the MCO, then declined over the later Miocene and Pliocene. The major changes in diversity over time were robust to sampling effects. Faunal composition changed episodically, with increasing proportions of rodents, lagomorphs, and carnivores and decreasing proportions of ungulates and proboscideans. The highest diversification rate occurred during the MCO with smaller but significant diversification rates later in the Neogene. The highest turnover rates occurred during and immediately following the MCO. Comparison of rodent faunas of the Great Basin and the Great Plains showed substantial differences in the timing and magnitude of diversification and changes in taxonomic composition. These patterns support the hypothesis that climate change over complex topography stimulated diversification in the Great Basin.
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Our understanding of macroevolutionary patterns of adaptive evolution has greatly increased with the advent of large-scale phylogenetic comparative methods. Widely used Ornstein–Uhlenbeck (OU) models can describe an adaptive process of divergence and selection. However, inference of the dynamics of adaptive landscapes from comparative data is complicated by interpretational difficulties, lack of identifiability among parameter values and the common requirement that adaptive hypotheses must be assigned a priori. Here, we develop a reversible-jump Bayesian method of fitting multi-optima OU models to phylogenetic comparative data that estimates the placement and magnitude of adaptive shifts directly from the data. We show how biologically informed hypotheses can be tested against this inferred posterior of shift locations using Bayes Factors to establish whether our a priori models adequately describe the dynamics of adaptive peak shifts. Furthermore, we show how the inclusion of informative priors can be used to restrict models to biologically realistic parameter space and test particular biological interpretations of evolutionary models. We argue that Bayesian model fitting of OU models to comparative data provides a framework for integrating of multiple sources of biological data—such as microevolutionary estimates of selection parameters and paleontological timeseries—allowing inference of adaptive landscape dynamics with explicit, process-based biological interpretations.
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The red (Ailurus fulgens) and giant (Ailuropoda melanoleuca) pandas are mammalian carnivores convergently adapted to a bamboo feeding diet. However, whereas Ailurus forages almost entirely on younger leaves, fruits and tender trunks, Ailuropoda relies more on trunks and stems. Such difference in foraging mode is considered a strategy for resource partitioning where they are sympatric. Here, we use finite-element analysis to test for mechanical differences and similarities in skull performance between Ailurus and Ailuropoda related to diet. Feeding simulations suggest that the two panda species have similar ranges of mechanical efficiency and strain energy profiles across the dentition, reflecting their durophagous diet. However, the stress distributions and peaks in the skulls of Ailurus and Ailuropoda are remarkably different for biting at all tooth locations. Although the skull of Ailuropoda is capable of resisting higher stresses than the skull of Ailurus, the latter is able to distribute stresses more evenly throughout the skull. These differences in skull biomechanics reflect their distinct bamboo feeding preferences. Ailurus uses repetitive chewing in an extended mastication to feed on soft leaves, and Ailuropoda exhibits shorter and more discrete periods of chomp-and-swallow feeding to break down hard bamboo trunks.
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The independent acquisition of high-crowned cheek teeth (hypsodonty) in several ungulate lineages (e.g., camels, equids, rhinoceroses) in the early to middle Miocene of North America has classically been used as an indication that savanna vegetation spread during this time. Implicit in this interpretation is the untested assumption that hypsodonty was an evolutionary response to feeding in open habitats, either due to a change in food source (from browse to graze) or to increased incorporation of airborne grit in the diet. I examined the adaptive explanation for hypsodonty in equids using criteria pertaining to process and pattern of adaptations set up in the comparative-methods literature. Specifically, I tested whether hypsodonty appeared coincident with or just after the spread of open, grass-dominated habitats in the Great Plains of North America. Phytolith (plant opal) analysis of 99 phytolith assemblages extracted from sediment samples from Montana/Idaho, Nebraska/Wyoming, and Colorado were used to establish the first continuous record of middle Eocene-late Miocene vegetation change in the northern to Central Great Plains. This record was compared with the fossil record of equids from the same area in a phylogenetic framework. The study showed that habitats dominated by C3 grasses were established in the Central Great Plains by early late Arikareean (≥21.9 Ma), at least 4 Myr prior to the emergence of hypsodont equids (Equinae). Nevertheless, the adaptive hypothesis for hypsodonty in equids could not be rejected, because the earliest savanna-woodlands roughly co-occurred with members of the grade constituting the closest outgroups to Equinae ("Parahippus") showing mesodont dentition. Explanations for the slow evolution of full hypsodonty may include weak and changing selection pressures and/or phylogenetic inertia. These results suggest that care should be taken when using functional morphology alone to reconstruct habitat change.
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▪ Abstract The history of carnivorous mammals is characterized by a series of rise-and-fall patterns of diversification in which declining clades are replaced by phylogenetically distinct but functionally similar clades. Seven such examples from the last 46 million years are described for North America and Eurasia. In three of the seven turnover events, competition with replacement taxa may have driven the decline of formerly dominant taxa. In the remaining four this is less likely because inferred functional similarity was minimal during the interval of temporal overlap between clades. However, competition still may have been important in producing the rise-and-fall pattern through suppression of evolution within replacement taxa; as long as the large carnivore ecospace was filled, the radiation of new taxa into that ecospace was limited, only occurring after the extinction of the incumbents. The apparently inevitable decline of incumbent taxa may reflect the tendency for clades of large carnivorous mamm...
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Multiple episodes of rapid and gradual climatic changes influenced the evolution and ecology of mammalian species and communities throughout the Cenozoic. Climatic change influenced the abundance, genetic diversity, morphology, and geographic ranges of individual species. Within communities these responses interacted to catalyze immigration, speciation, and extinction. Combined they affected long-term patterns of community stability, functional turnover, biotic turnover, and diversity. Although the relative influence of climate on particular evolutionary processes is oft debated, an understanding of processes at the root of biotic change yields important insights into the complexity of mammalian response. Ultimately, all responses trace to events experienced by populations. However, many such processes emerge as patterns above the species level, where shared life history traits and evolutionary history allow us to generalize about mammalian response to climatic change. These generalizations provide the gr...
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The evolution and subsequent ecological expansion of grasses (Poaceae) since the Late Cretaceous have resulted in the establishment of one of Earth's dominant biomes, the temperate and tropical grasslands, at the expense of forests. In the past decades, several new approaches have been applied to the fossil record of grasses to elucidate the patterns and processes of this ecosystem transformation. The data indicate that the development of grassland ecosystems on most continents was a multistage process involving the Paleogene appearance of (C3 and C4) open-habitat grasses, the mid-late Cenozoic spread of C3 grass-dominated habitats, and, finally, the Late Neogene expansion of C4 grasses at tropical-subtropical latitudes. The evolution of herbivores adapted to grasslands did not necessarily coincide with the spread of open-habitat grasses. In addition, the timing of these evolutionary and ecological events varied between regions. Consequently, region-by-region investigations using both direct (plant fossil...
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Background Development of phylogenetic methods that do not rely on fossils for the study of evolutionary processes through time have revolutionized the field of evolutionary biology and resulted in an unprecedented expansion of our knowledge about the tree of life. These methods have helped to shed light on the macroevolution of many taxonomic groups such as the placentals (Mammalia). However, despite the increase of studies addressing the diversification patterns of organisms, no synthesis has addressed the case of the most diversified mammalian clade: the Rodentia. Results Here we present a rodent maximum likelihood phylogeny inferred from a molecular supermatrix. It is based on 11 mitochondrial and nuclear genes that covers 1,265 species, i.e., respectively 56% and 81% of the known specific and generic rodent diversity. The inferred topology recovered all Rodentia clades proposed by recent molecular works. A relaxed molecular clock dating approach provided a time framework for speciation events. We found that the Myomorpha clade shows a greater degree of variation in diversification rates than Sciuroidea, Caviomorpha, Castorimorpha and Anomaluromorpha. We identified a number of shifts in diversification rates within the major clades: two in Castorimorpha, three in Ctenohystrica, 6 within the squirrel-related clade and 24 in the Myomorpha clade. The majority of these shifts occurred within the most recent familial rodent radiations: the Cricetidae and Muridae clades. Using the topological imbalances and the time line we discuss the potential role of different diversification factors that might have shaped the rodents radiation. Conclusions The present glimpse on the diversification pattern of rodents can be used for further comparative meta-analyses. Muroid lineages have a greater degree of variation in their diversification rates than any other rodent group. Different topological signatures suggest distinct diversification processes among rodent lineages. In particular, Muroidea and Sciuroidea display widespread distribution and have undergone evolutionary and adaptive radiation on most of the continents. Our results show that rodents experienced shifts in diversification rate regularly through the Tertiary, but at different periods for each clade. A comparison between the rodent fossil record and our results suggest that extinction led to the loss of diversification signal for most of the Paleogene nodes.
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A B S T R A C T Mountains, ocean currents, forests, and swamps have played an important role in regulating global climate for hundreds of millions of years, but the truly novel event of the Cenozoic was the evolution and expansion of grasslands, with their uniquely coevolved grasses and grazers. Neogene expansion of the climatic and geographic range of grasslands at the expense of woodlands is now revealed by recent studies of paleosols, fossils, and their stable isotopic com-positions. Grasslands and their soils can be considered sinks for atmospheric CO 2 , CH 4 , and water vapor, and their Cenozoic evolution a contribution to long-term global climatic cooling. Grassland soils are richer in organic matter than are woodland and desert soils of comparable climates, and when eroded, their crumb clods form sediment unusually rich in organic matter. Grasslands also promote export of bicarbonate and nutrient cations to lakes and to the oceans where they stimulate productivity and C burial; this increased productivity and C burial occur because grasslands preferentially exploit fertile young soils in the first flush of weathering and their soils have a crumb structure with much higher internal surface area for weathering than soils of woodlands and deserts. Grasslands also promote regional climatic drying by virtue of their higher albedo and lower transpiration than woodlands of comparable climatic regions. Labile pools of C in grassland soils and their accelerated weathering rates early in soil development may also account for increased climatic instability over the past 40 m.yr. Unidirectional, stepwise, long-term climatic cooling, drying, and climatic instability may have been driven not by tectonic forcing but by the coevolution of grasses and grazers.
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Communities have been shaped in numerous ways by past climatic change; this process continues today. At the end of the Pleistocene epoch about 11,700 years ago, North American communities were substantially altered by the interplay of two events. The climate shifted from the cold, arid Last Glacial Maximum to the warm, mesic Holocene interglacial, causing many mammal species to shift their geographic distributions substantially. Populations were further stressed as humans arrived on the continent. The resulting megafaunal extinction event, in which 70 of the roughly 220 largest mammals in North America (32%) became extinct, has received much attention. However, responses of small mammals to events at the end of the Pleistocene have been much less studied, despite the sensitivity of these animals to current and future environmental change. Here we examine community changes in small mammals in northern California during the last 'natural' global warming event at the Pleistocene-Holocene transition and show that even though no small mammals in the local community became extinct, species losses and gains, combined with changes in abundance, caused declines in both the evenness and richness of communities. Modern mammalian communities are thus depauperate not only as a result of megafaunal extinctions at the end of the Pleistocene but also because of diversity loss among small mammals. Our results suggest that across future landscapes there will be some unanticipated effects of global change on diversity: restructuring of small mammal communities, significant loss of richness, and perhaps the rising dominance of native 'weedy' species.
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Continental biodiversity gradients result not only from ecological processes, but also from evolutionary and geohistorical processes involving biotic turnover in landscape and climatic history over millions of years. Here, we investigate the evolutionary and historical contributions to the gradient of increasing species richness with topographic complexity. We analysed a dataset of 418 fossil rodent species from western North America spanning 25 to 5 Ma. We compared diversification histories between tectonically active (Intermontane West) and quiescent (Great Plains) regions. Although diversification histories differed between the two regions, species richness, origination rate and extinction rate per million years were not systematically different over the 20 Myr interval. In the tectonically active region, the greatest increase in originations coincided with a Middle Miocene episode of intensified tectonic activity and global warming. During subsequent global cooling, species richness declined in the montane region and increased on the Great Plains. These results suggest that interactions between tectonic activity and climate change stimulate diversification in mammals. The elevational diversity gradient characteristic of modern mammalian faunas was not a persistent feature over geologic time. Rather, the Miocene rodent record suggests that the elevational diversity gradient is a transient feature arising during particular episodes of Earth's history.
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Since 65 million years ago (Ma), Earth's climate has undergone a significant and complex evolution, the finer details of which are now coming to light through investigations of deep-sea sediment cores. This evolution includes gradual trends of warming and cooling driven by tectonic processes on time scales of 105to 107 years, rhythmic or periodic cycles driven by orbital processes with 104- to 106-year cyclicity, and rare rapid aberrant shifts and extreme climate transients with durations of 103 to 105 years. Here, recent progress in defining the evolution of global climate over the Cenozoic Era is reviewed. We focus primarily on the periodic and anomalous components of variability over the early portion of this era, as constrained by the latest generation of deep-sea isotope records. We also consider how this improved perspective has led to the recognition of previously unforeseen mechanisms for altering climate.
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The evolution of cursorial adaptations in Tertiary (65-1.65 Myr ago) carnivores has been a contentious issue. Most such studies have focused on the relationship between hind limb proportions and running speed. Here, we show morphometrically that in extant carnivores, the elbow joint has evolved in two distinct directions with mutually exclusive implications for locomotor ability and prey procurement. Some carnivores retain supinatory ability, allowing them to manipulate prey and other items with the forepaws. Such carnivores can become very large. Other carnivores lose the ability to supinate and become cursors. This allows for only moderate size increase. Modern carnivores above ca. 20 kg body mass are committed to one or other of these strategies. This threshold coincides with a postulated threshold in carnivore physiology. The biaxial pattern mostly follows phylogenetic lines, but a strong selective regime can override this signal, as shown by the extant cheetah. Oligocene (33.7-23.8 Myr ago) and early-middle Miocene (23.8-11.2 Myr ago) carnivores follow the same pattern, though in the Miocene the pattern is shifted towards larger body mass, which may be owing to the extraordinary richness of browsing ungulates at this time.
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An elongate body with reduced or absent limbs has evolved independently in many ectothermic vertebrate lineages. While much effort has been spent examining the morphological pathways to elongation in these clades, quantitative investigations into the evolution of elongation in endothermic clades are lacking. We quantified body shape in 61 musteloid mammals (red panda, skunks, raccoons, and weasels) using the head‐body elongation ratio. We also examined the morphological changes that may underlie the evolution towards more extreme body plans. We found that a mustelid clade comprised of the subfamilies Helictidinae, Guloninae, Ictonychinae, Mustelinae, and Lutrinae exhibited an evolutionary transition towards more elongate bodies. Furthermore, we discovered that elongation of the body is associated with the evolution of other key traits such as a reduction in body size and a reduction in forelimb length but not hindlimb length. This relationship between body elongation and forelimb length has not previously been quantitatively established for mammals but is consistent with trends exhibited by ectothermic vertebrates and suggests a common pattern of trait covariance associated with body shape evolution. This study provides the framework for documenting body shapes across a wider range of mammalian clades to better understand the morphological changes influencing shape disparity across all vertebrates. This article is protected by copyright. All rights reserved
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A recent pair of articles published in the journal Evolution presented a test for assessing the validity of hierarchical macroevolutionary models. The premise of the test is to compare numerical point estimates of parameters from two levels of analysis; if the estimates differ, the hierarchical model is purportedly flawed. The articles in question (Meyer and Wiens 2017; Meyer et al. 2018) apply their proposed test to BAMM, a scientific software program that uses a Bayesian mixture model to estimate rates of evolution from phylogenetic trees. The authors use BAMM to estimate rates from large phylogenies (n > 60 tips) and they apply the method separately to subclades within those phylogenies (median size: n = 3 tips); they find that point estimates of rates differ between these levels and conclude that the method is flawed, but they do not test whether the observed differences are statistically meaningful. There is no consideration of sampling variation and its impact at any level of their analysis. Here, I show that numerical differences across groups that they report are fully explained by a failure to account for sampling variation in their point estimates. Variance in evolutionary rate estimates - from BAMM and all other methods - is an inverse function of clade size; this variance is extreme for clades with 5 or fewer tips (e.g., 70% of clades in the focal study). The articles in question rely on negative results that are easily explained by low statistical power to reject their preferred null hypothesis, and this low power is a trivial consequence of high variance in their point estimates. I describe additional mathematical and statistical mistakes that render the proposed testing framework invalid on first principles. Evolutionary rates are no different than any other population parameters we might wish to estimate, and biologists should use the training and tools already at their disposal to avoid erroneous results that follow from the neglect of variance.
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As a result of the process of descent with modification, closely related species tend to be similar to one another in a myriad different ways. In statistical terms, this means that traits measured on one species will not be independent of traits measured on others. Since their introduction in the 1980s, phylogenetic comparative methods (PCMs) have been framed as a solution to this problem. In this paper, we argue that this way of thinking about PCMs is deeply misleading. Not only has this sowed widespread confusion in the literature about what PCMs are doing but has led us to develop methods that are susceptible to the very thing we sought to build defenses against - unreplicated evolutionary events. Through three Case Studies, we demonstrate that the susceptibility to singular events is indeed a recurring problem in comparative biology that links several seemingly unrelated controversies. In each Case Study we propose a potential solution to the problem. While the details of our proposed solutions differ, they share a common theme: unifying hypothesis testing with data-driven approaches (which we term "phylogenetic natural history") to disentangle the impact of singular evolutionary events from that of the factors we are investigating. More broadly, we argue that our field has, at times, been sloppy when weighing evidence in support of causal hypotheses. We suggest that one way to refine our inferences is to re-imagine phylogenies as probabilistic graphical models; adopting this way of thinking will help clarify precisely what we are testing and what evidence supports our claims.
Article
To study the evolution of several quantitative traits, the classical phylogenetic comparative framework consists of a multivariate random process running along the branches of a phylogenetic tree. The Ornstein-Uhlenbeck (OU) process is sometimes preferred to the simple Brownian Motion (BM) as it models stabilizing selection toward an optimum. The optimum for each trait is likely to be changing over the long periods of time spanned by large modern phylogenies. Our goal is to automatically detect the position of these shifts on a phylogenetic tree, while accounting for correlations between traits, which might exist because of structural or evolutionary constraints. We show that, in the presence of shifts, phylogenetic Principal Component Analysis (pPCA) fails to decorrelate traits efficiently, so that any method aiming at finding shifts needs to deal with correlation simultaneously. We introduce here a simplification of the full multivariate OU model, named scalar OU (scOU), which allows for noncausal correlations and is still computationally tractable. We extend the equivalence between the OU and a BM on a re-scaled tree to our multivariate framework. We describe an Expectation Maximization algorithm that allows for a maximum likelihood estimation of the shift positions, associated with a new model selection criterion, accounting for the identifiability issues for the shift localization on the tree. The method, freely available as an R-package (PhylogeneticEM) is fast, and can deal with missing values. We demonstrate its efficiency and accuracy compared to another state-of-the-art method (l1ou) on a wide range of simulated scenarios, and use this new framework to re-analyze recently gathered datasets on New World Monkeys and Anolis lizards.
Article
Through the Cenozoic, paleoclimate records show general trends of global cooling and increased aridity, and environments in North America shifted from predominantly forests to more open habitats. Paleobotanical records indicate grasses were present on the continent in the Eocene; however, paleosol and phytolith studies indicate that open habitats did not arise until the late Eocene or even later in the Oligocene. Studies of large mammalian herbivores have documented changes in ecomorphology and community structure through time, revealing that shifts in mammalian morphology occurred millions of years after the environmental changes thought to have triggered them. Smaller mammals, like rodents and lagomorphs, should more closely track climate and habitat changes due to their shorter generation times and smaller ranges, but these animals have received much less study. To examine changes in smaller mammals through time, we have assembled and analyzed an ecomorphological database of all North American rodent and lagomorph species.
Article
The proportions of the limb bones of tetrapods contribute to the energetic costs of locomotion. Consequently, they can be used to classify locomotor type and can inform hypotheses about changes in community structure. We examined mechanical advantage in the limbs of North American Oligocene and Miocene ungulates (Artiodactyla and Perissodactyla), with the expectation that the distribution of limb morphologies would change with the spread of grass-dominated plant communities; that is, we expect to find morphological optimization for efficient high-speed locomotion with more open habitats. We assess changes in the occupation of locomotor ecomorphospace (LEMS) through time using measurements of the lengths of stylopods and zeugopods of North American ungulate species. Analysis of LEMS reveals significant changes in dominant ungulate locomotor morphology between Oligocene and Miocene faunas. Oligocene ungulates show less variation in LEMS than Miocene ungulates. Artiodactyls show a significant selection towards cursorial morphologies (p < 0.01) in the Miocene. A majority of artiodactyls are non-cursorial in the Oligocene, but only one family occupies the non-cursorial morphospace in the Miocene. Perissodactyls maintain similar levels of disparity in limb proportions in the Miocene as in the Oligocene (p = 0.72), but more perissodactyls occupy the cursorial morphospace in the Miocene than the Oligocene. Our results suggest that the shift from closed to relatively open habitat structure from the Oligocene to the Miocene is associated with a significant change in the proximal limb locomotor anatomy and associated limb mechanics of North American ungulate species.
Article
Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimmensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically.
Article
1. We present mvMORPH, a package of multivariate phylogenetic comparative methods for the R statistical environment. mvMORPH is freely available on the CRAN package repository (http://cran.r-project.org/web/packages/mvMORPH/). 2. mvMORPH allows fitting a range of multivariate evolutionary models under a maximum-likelihood criterion. Initially developed in the context of phylogenetic analysis of multiple morphometric traits, its use can be extended to any biological dataset with one or multiple covarying continuous traits. All the fitting models include the possibility to use SIMMAP-like mapping, which may be useful for fitting changes along lineages at a given point in time. All models provide diagnostic metrics for convergence and reliability of estimates, as well as the possibility to include trait measurement errors in model estimates. 3. New features provided by the mvMORPH package include the possibility of fitting models with changes in the mode of evolution along the phylogeny, which will be particularly meaningful in comparative analyses that include extinct taxa, e.g., when testing changes in evolutionary mode associated with global biotic/abiotic events. 4. We briefly describe the models already included in mvMORPH, and provide some demonstration of the use of the package with two simulated worked examples.
Article
In Measuring and Reasoning, Fred L. Bookstein examines the way ordinary arithmetic and numerical patterns are translated into scientific understanding, showing how the process relies on two carefully managed forms of argument: Abduction: the generation of new hypotheses to accord with findings that were surprising on previous hypotheses, and Consilience: the confirmation of numerical pattern claims by analogous findings at other levels of measurement. These profound principles include an understanding of the role of arithmetic and, more importantly, of how numerical patterns found in one study can relate to numbers found in others. They are illustrated through numerous classic and contemporary examples arising in disciplines ranging from atomic physics through geosciences to social psychology. The author goes on to teach core techniques of pattern analysis, including regression and correlation, normal distributions, and inference, and shows how these accord with abduction and consilience, first in the simple setting of one dependent variable and then in studies of image data for complex or interdependent systems. More than 200 figures and diagrams illuminate the text. The book can be read with profit by any student of the empirical nature or social sciences and by anyone concerned with how scientists persuade those of us who are not scientists why we should credit the most important claims about scientific facts or theories.
Article
The aim of macroevolutionary research is to understand pattern and process in phenotypic evolution and lineage diversification at and above the species level. Historically, this kind of research has been tackled separately by palaeontologists, using the fossil record, and by evolutionary biologists, using phylogenetic comparative methods.Although both approaches have strengths, researchers gain most power to understand macroevolution when data from living and fossil species are analysed together in a phylogenetic framework. This merger sets up a series of challenges – for many fossil clades, well‐resolved phylogenies based on morphological data are not available, while placing fossils into phylogenies of extant taxa and determining their branching times is equally challenging. Once methods for building such trees are available, modelling phenotypic and lineage diversification using combined data presents its own set of challenges.The five papers in this Special Feature tackle a disparate range of topics in macroevolutionary research, from time calibration of trees to modelling phenotypic evolution. All are united, however, in implementing novel phylogenetic approaches to understand macroevolutionary pattern and process in or using the fossil record. This Special Feature highlights the benefits that may be reaped by integrating data from living and extinct species and, we hope, will spur further integrative work by empiricists and theoreticians from both sides of the macroevolutionary divide.
Article
In this article, we investigate convergent evolution toward durophagy in carnivoran skull shape using geometric morphometrics in a sample of living and extinct species. Principal components analysis indicate that, in spite of the different dietary resources consumed by durophages-that is, bone-crackers and bamboo-feeders-both groups of carnivorans share portions of skull phenotypic spaces. We identify by discriminant analyses a shared set of adaptations toward durophagy in the skull of carnivores. However, ancestral states indicate that although durophages reached similar phenotypes, the evolutionary pathways that they followed are different depending upon the family to which they belong. Furthermore, while the carnivoran cranium more closely reflects the nature of the resources consumed-that is, soft or hard and tough items-the mandible shows particular feeding adaptations-that is, bamboo or bone. This finding supports the interpretation that the mandible has more evolutionary plasticity than the cranium, which is more limited to evolve toward a particular feeding adaptation. However, we find that the shapes of the cranium and the mandible are highly integrated for the whole order Carnivora. Published studies of teratological cats and dogs indicate that the role of internal constraints in shaping this pattern of integration is absent or weak and malleable by selection.
Article
Comparative biologists often attempt to draw inferences about tempo and mode in evolution by comparing the fit of evolutionary models to phylogenetic comparative data consisting of a molecular phylogeny with branch lengths and trait measurements from extant taxa. These kinds of approaches ignore historical evidence for evolutionary pattern and process contained in the fossil record. In this article, we show through simulation that incorporation of fossil information dramatically improves our ability to distinguish among models of quantitative trait evolution using comparative data. We further suggest a novel Bayesian approach that allows fossil information to be integrated even when explicit phylogenetic hypotheses are lacking for extinct representatives of extant clades. By applying this approach to a comparative dataset comprising body sizes for caniform carnivorans, we show that incorporation of fossil information not only improves ancestral state estimates relative to those derived from extant taxa alone, but also results in preference of a model of evolution with trend toward large body size over alternative models such as Brownian motion or Ornstein-Uhlenbeck processes. Our approach highlights the importance of considering fossil information when making macroevolutionary inference, and provides a way to integrate the kind of sparse fossil information that is available to most evolutionary biologists.
Article
Fifteen functionally significant aspects of skull morphology were measured on skulls of 36 additional species of carnivores to complete a survey of skull shape in modern fissiped (land) carnivores that includes most of the living genera. The measurements were transformed to dimensionless variables based on the residuals from allometric equations, and were analysed singly and in a 10 variable principal components analysis. An initial study of 62 species of viverrids, canids, mustelids and felids had shown those families to be distinguished from each other by the functionally significant measurements. However, among the additional 36 species, some procyonids, ursids and mustelids display a range of diversity of skull morphology that overlaps that of the other families and diminishes the potential value of the measurements as taxonomic characters. Intraspecific variation is presented for 12 species, and is low enough to allow use of some features as species level diagnostic characters. The lack of correlation between diet and functionally significant aspects of skull morphology among omnivorous carnivores, and the absence of certain skull shapes among carnivores are discussed.
Article
Fifteen variables, selected primarily to reflect functionally significant aspects of cranial morphology, were measured on one skull each of 62 species of modern carnivores, including viverrids, canids, mustelids and felids. To allow comparisons between species of different sizes without the potentially confounding effects of allometric shape changes, the measurements were transformed to dimensionless variables, based on the residuals from allometric equations. Fourteen out of 15 of the transformed variables distinguish one or more of the four family groups and the rotated first two axes of a principal components analysis distinguish all four families from each other. The following functional hypotheses are proposed: mustelids and felids have the most powerful bites and canids the weakest among the four family groups studied; mustelids and, to a lesser degree, felids have more powerful neck musculature than do canids and viverrids; and visual abilities are best developed among felids and least developed among mustelids. The first two functional hypotheses suggest possible differences in killing behaviour, which are supported by a preliminary survey of the literature on such behaviour. Allometric analysis of the 15 cranial measures shows that the neurocranial components scale with negative allometry, while most of the other measures scale approximately isometrically.
Article
An ecomorphological study of extant small carnivorans demonstrates that dietary groups can be distinguished using quantitative morphological characters. Small (<10 kg) modern carnivorans were divided into three dietary classes: carnivores, insectivores and omnivores/hard-object feeders. Statistical analyses revealed differences between these classes including longer carnassial blades in carnivorans, as opposed to larger molar grinding areas, larger post-canine dentitions, and wider fourth premolars in omnivores/hard-object feeders. Insectivores are not consistently distinguished from other dietary types, although they do tend to have weaker dentaries and shorter temporalis muscle moment arms. These trends can be used to help interpret morphologies of taxa of uncertain ecologies, including fossil taxa.
Article
The evolutionary history of a clade has traditionally been studied through phylogenet-ics, and taxonomic diversity has been used as a crude proxy for morphological diversity. However, morphological diversification—beyond counting taxa—can provide a very different view of a clade's evolutionary history and allows the investigation of patterns and timing of morphological evolution. In this paper I use dentition to document the pattern of morphological and taxonomic diversi-fication of Carnivoramorpha and mammalian meat eaters in North America. Using the dentition permits ecological inferences to be made, because teeth and diet are closely related. I present a method developed to describe the entire dentition of the Carnivoramorpha and other mammalian meat eaters (Creodonta). Morphological diversification is measured by dental disparity, using the mean pairwise dissimilarity among species. I test the following hypotheses: (1) Morphological diversification was suppressed relative to tax-onomic diversification, early in the evolutionary history of Carnivoramorpha; and (2) once an ef-ficient system for consuming meat evolved, the dental system remained relatively unchanged. The first hypothesis is rejected. Taxonomic and morphological diversity increase together through the clade's early evolution. There is no evidence of a morphological release in the carni-voramorphans with the demise of creodonts. The second hypothesis is supported. The ecological group ''mammalian meat eaters'' rapidly diversified morphologically and reached its maximum disparity early in its history, after which the dental system remained relatively unchanged.
Article
Fast-running, long-legged pursuit carnivores are familiar members of the present-day ecosystem, and it has been assumed that extinct large predators took similar ecomorphological roles (i.e., were wolf avatars) in past faunas. While these fossil taxa may also have been meat-specialists, we present evidence from limb morphology to show that there was no modern type of pursuit predator until the latest Tertiary. In contrast, ungulates evolved longer legs similar to those of present-day cursorial taxa by the middle Tertiary, some 20 million years earlier. These data suggest the need for the reevaluation of many classical evolutionary stories, not only about assignation of fossil taxa to a wolf-like mode of predatory behavior, but also to issues such as the coevolution of long legs and fast running speeds between predator and prey, and even the implicit assumption that cursorial morphologies are primarily an adaptation for speed. We conclude that evolutionary change in ungulate limb morphologies represents an adaptation to decrease transport costs in association with Tertiary climatic changes and that the present-day predation mode of long distance pursuit is a Plio-Pleistocene phenomenon, related to the development of colder and more arid climates.
Article
The North American grassland biome first appeared around 18 Ma in the mid Miocene. The familiar story of the Neogene evolution of this biome is of the replacement of ungulates (hoofed mammals) having a primarily browsing diet by the more derived grazing ungulates. However, new data show a more complicated pattern of faunal succession. There was a maximum taxonomic diversity of ungulates at 16–14 Ma, including a large number of grazers, and the subsequent decline in overall diversity was largely due to the decline of the browsers, with little corresponding increase in the grazers. Additionally the mid Miocene faunas (∼18–12 Ma) contained a much greater number of browsers than any comparable present-day habitat. We discuss possible explanations for these non-analogous grassland faunas, including the possibility that the primary productivity of the vegetation was greater in the early to middle Miocene than it is today. One possible explanation for increased primary productivity is higher Miocene levels of atmospheric carbon dioxide than in the present day. The proposed difference in vegetational productivity also may explain why horses radiated as the main grazers in North America, in contrast to the radiation of antelope in the Plio–Pleistocene African grasslands.
Article
The North American grassland biome forst appeared around 18Ma in the mid-Miocene. The familiar story of the Neogene evolution of this biome is of a replacement of ungulates(hoofed mammals)having a primarily browsing diet by the more derived grazing ungualtes. However, new data show a more complicated pattern of faunal succession. There was a maximum taxonomic diversity of ungulates at 16-18Ma, including a large number of grazers, and the subsequent decline in overall diversity was largely due to the decline of the browsers, with little corresponding increase in the grazers. Additionally the mid-Miocene faunas (~18-12Ma) contained a much greater number of browsers than any comparable present-day habitat. We discuss the possible explanations for these non-analagous grassland faunas, including the possibility that the primary production of teh vegetation was greater in the early to middle Miocene than it is today. One possible explanation for increased primary productivity is higher Miocene levels of atmospheric carbon dioxide than in the present day. The propose difference in vegetational productivity also may explain why horses radiated as the main grazers in North America, in contrast to the radiation of antelope in the Plio-Pleistocene African grasslands.
Article
High-crowned (hypsodont) teeth are widely found among both extant and extinct mammalian herbivores. Extant grazing ungulates (hoofed mammals) have hypsodont teeth (a derived condition), and so extinct hypsodont forms have usually been presumed to have been grazers. Thus, hypsodonty among ungulates has, over the past 150 years, formed the basis of widespread palaeoecological interpretations, and has figured prominently in the evolutionary study of the spread of grasslands in the mid Cenozoic. However, perceived inconsistencies between levels of hypsodonty and dental wear patterns in both extant and extinct ungulates have caused some workers to reject hypsodonty as a useful predictive tool in palaeobiology, a view that we consider both misguided and premature.
Article
The evolution of grasses using C4 photosynthesis and their sudden rise to ecological dominance 3 to 8 million years ago is among the most dramatic examples of biome assembly in the geological record. A growing body of work suggests that the patterns and drivers of C4 grassland expansion were considerably more complex than originally assumed. Previous research has benefited substantially from dialog between geologists and ecologists, but current research must now integrate fully with phylogenetics. A synthesis of grass evolutionary biology with grassland ecosystem science will further our knowledge of the evolution of traits that promote dominance in grassland systems and will provide a new context in which to evaluate the relative importance of C4 photosynthesis in transforming ecosystems across large regions of Earth.