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Morphological Evolution of the Scapula in Tree Squirrels, Chipmunks, and Ground Squirrels (Sciuridae): An Analysis Using Thin-Plate Splines
Abstract
The mammalian scapula, like many bones, is a single structural element that serves as an attachment site for several muscles. The goal of this study was to determine whether the scapula evolves as an integrated unit, or as a collection of distinct parts. Shape differences among the scapulae of tree squirrels, chipmunks, and ground squirrels were described using thin-plate spline analysis. This technique produces a geometric description of shape differences that can be decomposed into a series of components ranging in scale from features that span the entire form to features that are highly localized. Shape differences among tree squirrel scapulae were found only in large-scale features, indicating spatially integrated shape change. Chipmunks and ground squirrels differ from tree squirrels in several features, but shared differences reflecting divergence of their common ancestor were found only in the small-scale features. Divergence of ground squirrels from the common ancestor involved some large-scale changes but was dominated by small-scale changes. Divergence of chipmunks was dominated by large-scale changes. Thus, the scapula evolved as an integrated unit during some transitions but as a collection of distinct parts during others. These results suggest that evolutionary patterns of the postcranial skeleton may be as complex as the patterns that have been described for skulls and feeding mechanisms.
... In this study, the Class I average was taken as the initial geometry and the mean Class III configuration as the final geometry. The TPS analysis (Swiderski, 1993;Bookstein, 1989) was conducted to map points within the midfacial and mandibular anatomical landmarks from the initial to the final cephalographs. The TPS mapping function can be described by a physical metaphor in which the landmarks of one form located on an infinitely thin metal plate are deformed so that the height over each landmark is equal to the coordinates of the corresponding point on the other form (Swiderski, 1993;Bookstein, 1989). ...
... The TPS analysis (Swiderski, 1993;Bookstein, 1989) was conducted to map points within the midfacial and mandibular anatomical landmarks from the initial to the final cephalographs. The TPS mapping function can be described by a physical metaphor in which the landmarks of one form located on an infinitely thin metal plate are deformed so that the height over each landmark is equal to the coordinates of the corresponding point on the other form (Swiderski, 1993;Bookstein, 1989). We have taken 5100 and 6200 triangular elements for midface and mandible which were generated by TPS. ...
... The new technique of geometric morphometrics, called TPS analysis (Bookstein, 1989), generates useful illustrations of size and shape differences, and displays more information on morphological differences than in the past. The TPS analysis utilizes an interpolation function that maps points or landmarks of a reference configuration onto the corresponding location of another configuration, and further, it can plot the morphological differences between two landmark configurations by way of a transformation grid (Swiderski, 1993;Yaroch, 1996). ...
The method of strain tensor (ST) analysis efficiently demonstrates the morpho-logical differences in skeletal jaw growth and provides more information for orth-odontic diagnosis and orthopedic therapy of jaw disharmonies. The purpose of this study was to investigate midfacial and mandibular size and shape differences in a sample of normal Class I molar occlusion and Class III malocclusion. Fifty Chinese boys aged 10-12 years, each occlusal group of 25 subjects, have been selected. The results indicated that statistically significant differences in midfacial and mandibular configurations between Class I occlusion and Class III malocclusion occurred at P< 0.01 levels. The mandibular corpus of Class III malocclusion was larger than that of Class I occlusion and the extension direction of growth tensors was chiefly mani-fested along the long axis of general mandibular morphology. In contrast, the midfacial size of Class III malocclusion was smaller than that of Class I occlusion and a hori-zontal reduction was observed at the posterior midface. Shape differences in the midface and mandible manifested for the two occlusal types. The present investiga-tion with a new geometric morphometrics (ST analysis) provides more information and better understanding of the midfacial and mandibular morphology and growth pattern in Class III growing children.
... TPS models shape differences as deformations among a set of homologous landmarks, which are digitized on the included specimens. The thin plate spline function interpolates a surface that is fixed at the landmarks, and is computed so as to minimize overall bending energy, implying minimizing spatially localized information (Bookstein, 1991;Swiderski, 1993;Zelditch et al., 2000Zelditch et al., , 2004. This has important implications for interpretation because any given morphological change may always be interpreted as a singular feature but this is, by default, unparsimonious. ...
... Other displacements are non-affine, and are localized changes in one region relative to others. These can be decomposed by eigen analyses of a bending energy matrix into non-affine components of a progressively more localized nature (Bookstein, 1991;Swiderski, 1993;Zelditch et al., 2000Zelditch et al., , 2004. ...
... By default, the consensus shape is oriented by its principal components axis. An initial affine X, Y component describes parallel changes in shape, and succeeding non-affine components are generated in the order of least localized (small eigenvalues) to most localized (large eigenvalues) (Bookstein, 1991;Swiderski, 1993;Zelditch et al., 2000Zelditch et al., , 2004. ...
The great North American Pleistocene pantherine felid Panthera atrox has had a turbulent phylogenetic history, and has been claimed to show affinities to both the jaguar and the tiger; currently, it is most often regarded as a subspecies of the extant lion. The cranial, mandibular, and dental morphology of Panthera atrox was compared with those of extant lions, jaguars, and tigers using bivariate, multivariate, and shape analyses. Results indicate that the skull of Panthera atrox shows lion affinities, but also deviates from lions in numerous aspects. Mandibular morphology is more similar to jaguars and tigers and, as with cranial morphology, the mandible shows a number of traits not present among extant pantherines. Multivariate analyses grouped Panthera atrox separately from other pantherines. Panthera atrox was no lion, and cannot be assigned to any of the extant pantherines; it constituted a separate species. A possible scenario for evolution of P. atrox is that it formed part of a pantherine lineage that entered the Americas in the mid-Pleistocene and gave rise to the extant jaguar and Panthera atrox in the late Pleistocene of North America. These studies suggest that previous models of lion biogeography are incorrect, and although lions may have been present in Beringia, they did not penetrate into the American mainland.
... More recent studies of scapular shape have used landmark-based geometric morphometrics (GM), an analysis of geometric information based on a configuration of landmarks independent of size, position, and orientation (Dryden and Mardia 1998) providing informative and intuitive graphic displays of shape changes. GM has been used to study scapular shape variation in several groups of vertebrates, including squirrels (Swiderski 1993), armadillos (Monteiro and Abe 1999), turtles (Depecker et al. 2006), rodents (Morgan 2009), and marsupials (Astúa 2009), as well as primates, although in this case the findings were inconsistent. Taylor and Slice (2005) used two-dimensional GM to compare the shape of the dorsal side of the scapula, including the fossae, the spine, and the acromion, of chimpanzees with that of gorillas. ...
... To minimize this, we kept the distance to the digital camera constant and oriented the scapulae with the plane defined by landmarks 3, 4, and 5 parallel to the plane of focus. The distortion caused by projecting all landmarks onto this plane will have its greatest effect on the acromion (Swiderski 1993), not affecting our analysis. After obtaining the digital images with a Canon EOS 550D digital camera we recorded the coordinates of the landmarks with tpsDig 2.16 software. ...
Hominoidea have adapted to various forms of locomotion, each of which has specific requirements that are reflected in the shape of the scapula. We compared several qualitative and quantitative methods for characterizing the dorsal side of the scapula to detect morphological differences that reflect the adaptations of the scapula to locomotor behaviors. Our sample included 55 specimens of Hominoidea, repre-senting five genera, including Homo, focusing specifically on the relative sizes of the scapular supraspinous and infranspinous fossae. In addition, we weighed the supra-spinatus and infraspinatus muscles of 23 of the specimens to examine the feasibility of extrapolating muscle characteristics from osteological data. Our findings con-firmed that the five genera exhibit significant differences in the relative size of the supraspinous and the infraspinous fossae that are related to their forms of locomotion. The supraspinous fossa was relatively small in Homo and Pongo but large in Pan, Gorilla, and Hylobates. The analysis of muscle weights showed that a substantial amount of information about soft tissues is lost in osteological analyses, leading us to recommend caution when drawing conclusions regarding forms of locomotion based only on osteological analyses.
... Previous works have analyzed characteristics of the long bones and autopodial skeleton of diverse caviomorphs and studied adaptive traits of these postcranial elements (Biknevicius 1993;Casinos et al. 1993;Vassallo 1998;Stein 2000;Elissamburu and Vizcaíno 2004;Weisbecker and Schmid 2007;Candela and Picasso 2008). Although several workers have analyzed the mammalian scapula using morphological and morphofunctional approaches (Lessertiseur and Saban 1967;Oxnard 1968;Hildebrand 1985;Price 1993;Swiderski 1993;Taylor 1997;Sargis 2002;Young 2004Young 2006, including caviomorph rodents (Lehmann 1963;Fernández et al. 2000;Seckel and Janis 2008), no comprehensive analyses have been made of the shoulder girdle of caviomorphs as a group. ...
... sliding points placed along outlines and allowed to change their spacing along the curves they describe; Bookstein 1997). Nine landmarks were selected on the basis of a qualitatitive analysis of shape variation in the sample, as well as previous studies (Swiderski 1993;Monteiro and Abe 1999;Young 2004), and digitized from digital photographs of the scapula in external view (Fig. 1, Table 2). I used the application MakeFan6 (Sheets 2003) to place alignment ''fans'' at equal angular displacements along the curved scapular outline, and nine semilandmarks were extracted along the craniodorsal outline of the scapula between landmarks (5) and (6) to describe the variably convex shape of the cranial border and angle (Fig. 2). ...
The scapula of the ecomorphologically diverse South American caviomorph rodents was studied through geometric morphometric techniques, using landmarks and semilandmarks to capture the shape of this complex morphological structure. Representatives of 33 species from all caviomorph superfamilies, as well as Hystrix cristata for comparisons, were analyzed. Marked differences in scapular shape were found among the major caviomorph lineages analyzed, particularly in the shape and length of the scapular spine and development of the great scapular notch. Shape differences were not influenced by body size, and only partially influenced by locomotor mode. Thus, at this scale of analysis, phylogenetic history seems to be the strongest factor influencing scapular shape. The scapular shape of erethizontids, chinchillids and Cuniculus paca could represent the less specialized state with respect to the highly differentiated scapula of octodontoids and most cavioids. In this sense, the characteristic scapular morphologies of octodontoids and cavioids could reflect particular functional capabilities and constraints associated with the evolution of prevalent locomotor modes within each lineage.
... Their elongated tails and sharp-clawed digits further enhance balance and grip in arboreal environments (Carrizo and Díaz 2013;Coutinho and Oliveira, 2017). Notably, similar morphofunctional specializations are observed in other groups of small mammals, associated with diverse locomotor habits and lifestyles, suggesting evolutionary convergence guided by natural selection (Swiderski 1993;Sargis 2002;Salton and Sargis 2008;Astúa 2009;Arregoitia et al. 2017;Tavares and Pessôa 2020;Carvalhaes et al. 2022). ...
Cerradomys, a genus of rodents with eight described species, primarily inhabits open vegetation areas in South America. Cerradomys goytaca, the only species endemic to coastal sandy plains, exhibits scansorial abilities and is frequently captured in trees. Typically, scansorial rodents display adaptations in the appendicular skeleton that facilitate climbing. We hypothesized that C. goytaca has developed locomotor specializations for a scansorial habit, differentiating it from other closely related species. To test this, we characterized scapular morphological variation in seven Cerradomys species from eastern Brazil using 2D geometric morphometrics on 211 adult specimens. A low but significant allometric effect was observed, explaining up to 3.2% of shape variation. Principal Component Analysis and Linear Discriminant Analysis (LDA) revealed interspecific differences in scapular shape, with C. goytaca exhibiting a relatively wider and shorter scapular blade. LDA indicated a tendency for species to occupy distinct regions of morphospace, despite partial overlap and the absence of complete morphological segregation. Among the species analyzed, C. goytaca was consistently distinct from its closest relative, C. subflavus. Its scapular morphology resembles that of other climbing mammals, suggesting recent morphological divergence likely driven by ecological pressures in the coastal sandy plains. These findings support our hypothesis and suggest that Cerradomys species exhibit anatomical variation that reflects adaptation to diverse habitats and locomotor behaviors.
... In trilobites, quantitative measurements have been used for the study of morphology for a very long time (Eldredge 1972(Eldredge , 1973. Quantitative measurements (e.g., linear distances or angles between anatomical landmarks, homologous landmarks) digitized on 2D pictures are usually used for such studies (Zelditch et al. 1992;Swiderski 1993;Elewa 2004). Nevertheless, while 2D quantitative analyses have advanced our understanding of the morphological relationships among trilobites (Smith and Lieberman 1999;Kim et al. 2002;Crônier et al. 2005Crônier et al. , 2015, 3D quantitative analyses have recently received the most attention, although not in phacopid trilobites. ...
Phacopid trilobites are well documented during the Paleozoic. Nevertheless, while 2D quantitative analyses have advanced our understanding of the morphological relationships among trilobites, the quantification of their morphological traits in 3D remains rarely documented. Based on two sets of morphological data (head and tail), 2D versus 3D shape quantification approaches were used to explore shape allometries as well as to explore how the shape variations can be explained by the phylogenetic relationships among phacopid trilobite species for the first time. We demonstrate that (1) there are similar patterns of morphological variability across taxa in 3D and 2D; (2) there are rather congruent results between 3D and 2D to discriminate taxa; (3) 2D and 3D landmarks capture different levels of detail, and the third dimension in 3D is very important for making taxonomic distinctions at the genus level; (4) there is congruity between 2D and 3D datasets for allometric patterns with results showing similar allometric slopes among species exhibiting a glabellar length decrease during growth leading to wider cephala; (5) the phylomorphospaces show tree branches that do not intersect, suggesting possible phylogenetic constraints on morphospace occupation for each species and supporting the idea that the Austerops and Morocops groups are sister clades that experienced different modes of morphological evolution; and (6) the morphological descriptors in morphometric analyses in 2D and 3D throughout phacopid evolution are effective.
... Specimens of E. interrupta (139) and the type material of E. interrupta, G. christyi and G. instabilis were used in the morphometric analysis. Eight homologous and repeatable landmarks (Swiderski 1993) on each shell (Fig. 1A) were digitized from photographs using tpsDig 1.40 (Rohlf 2004). Total shell length could not be used since most specimens of E. interrupta were missing early whorls due to erosion and/or breakage. ...
An examination of museum material indicated that the lectotypes of Goniobasis christyi Lea, 1862 and G. instabilis Lea, 1862, along with recent collections of putative Elimia interrupta (Haldeman, 1840), represent a new species separate from E. interrupta, sensu stricto. We propose the name E. christyi for the new species, and provide re-descriptions of it and E. interrupta.
... Using tpsDig2 (Rohlf, 2015), one of us (T.P.F.) positioned ten anatomical landmarks on each digital image (Fig. 1). The landmarks were selected based on their contribution to the characterization of both scapula shape and the main regions containing muscle insertions, which are associated with important locomotory functions (based on Swiderski, 1993;Astúa, 2009;Morgan, 2009). All landmark configurations were submitted to a generalized Procrustes analysis (GPA; Rohlf & Slice, 1990) in order to correct the raw coordinates by rotating, translating and rescaling them. ...
It is not a new concept that marsupials and placentals are distant and distinct clades among mammals. In South America, these animals coexist, occupy similar niches and, in some cases, are similar in appearance. This is especially true with respect to the locomotor categories of smaller rodents belonging to the family Cricetidae or, more specifically, the subfamily Sigmodontinae, compared with the marsupials of the Didelphidae family. In this study, we have investigated both the similarities and the differences between the two clades by examining locomotion-dependent adaptation, a crucial survival mechanism that has affected the morphology of both clades. We applied geometric morphometrics to quantify the shape of the scapula, which is a very adaptable structure. We found similar morphological adaptations between the clades, especially with respect to adaptation to life in trees. Moreover, Didelphidae are influenced by phylogenetic history to a greater extent than Sigmodontinae with regard to variation of scapula shape and allometry. These differences can be explained by the greater degree of body size variation that exists within the Didelphidae. Didelphidae have an ancient evolutionary history in South America compared with the Sigmodontinae, which have undergone a very successful and rapid diversification more recently.
... We therefore expected the femur to be informative for the question addressed herein. Various studies have been concerned with the comparison of the morphology of sciuromorph taxa with different locomotor behaviors (Parsons, 1894;Peterka, 1936;Bryant, 1945;Polyakova & Sokolov, 1965;Gambaryan, 1974;Stalheim-Smith, 1984;Swiderski, 1993;Thorington et al. 1997;Essner & Scheibe, 2002;Thorington & Santana, 2007;Hayssen, 2008;Mielke et al. 2018). However, except for the study of Hays- sen (2008), which investigated the relation between body mass and body length as well as tail length among different locomotor groups, we know of no publication that has accounted for a possible interplay of ecological and allometric constraints. ...
Sciuromorph rodents are a monophyletic group comprising about 300 species with a body mass range spanning three orders of magnitude and various locomotor behaviors that we categorized into arboreal, fossorial and aerial. The purpose of this study was to investigate how the interplay of locomotor ecology and body mass affects the morphology of the sciuromorph locomotor apparatus. The most proximal skeletal element of the hind limb, i.e. the femur, was selected, because it was shown to reflect a functional signal in various mammalian taxa. We analyzed univariate traits (effective femoral length, various robustness variables and the in‐levers of the muscles attaching to the greater, third and lesser trochanters) as well as femoral shape, representing a multivariate trait. An ordinary least‐squares regression including 177 species was used to test for a significant interaction effect between body mass and locomotor ecology on the variables. Specifically, it tested whether the scaling patterns of the fossorial and aerial groups differ when compared with the arboreal, because the latter was identified as the ancestral sciuromorph condition via stochastic character mapping. We expected aerial species to display the highest trait values for a given body mass as well as the steepest slopes, followed by the arboreal and fossorial species along this order. An Ornstein–Uhlenbeck regression fitted to a phylogenetically pruned dataset of 140 species revealed the phylogenetic inertia to be very low in the univariate traits, hence justifying the utilization of standard regressions. These variables generally scaled close to isometry, suggesting that scaling adjustments might not have played a major role for most of the femoral features. Nevertheless, the low phylogenetic inertia indicates that the observed scaling patterns needed to be maintained during sciuromorph evolution. Significant interaction effects were discovered in the femoral length, the centroid size of the condyles, and the in‐levers of the greater and third trochanters. Additionally, adjustments in various femoral traits reflect the acquisitions of fossorial and aerial behaviors from arboreal ancestors. Using sciuromorphs as a focal clade, our findings exemplify the importance of statistically accounting for potential interaction effects of different environmental factors in studies relating morphology to ecology.
... There have been many papers concerned with how one can make use of the new techniques of geometric morphometrics in systematics -especially for phylogeny estimation. Zelditch et al. (1992Zelditch et al. ( , 1993, , Swiderski (1993), and Fink and Zelditch (1995) used partial warp scores to search for variables that could be used in cladistic studies. They compared regressions of individual partial warps to obtain discrete characters and used linear (Wagner) parsimony to estimate a phylogeny. ...
... Most studies that have used geometric morpho- metrics to explore shape variation in an evolutionary framework have focused on vertebrates: for example, to study transformations in skull shape, scapula shape, body form, etc. (Swiderski, 1993;Zelditch, Fink & Swiderski, 1995;Oettlé, Pretorius & Steyn, 2005;Stayton, 2005). In contrast, relatively few such studies have focused on insects. ...
A geometric morphometric analysis was conducted on wing-vein landmarks on exemplar species of the family
Simuliidae of the following genera: Parasimulium, Gymnopais, Twinnia, Helodon, Prosimulium, Greniera,
Stegopterna, Tlalocomyia, Cnephia, Ectemnia, Metacnephia, Austrosimulium, and Simulium. Generalized least
squares superimposition was performed on landmarks, followed by a principal component analysis on resulting Procrustes distances. Patterns of shape change along the principal component axes were visualized using the thin-plate spline. The analysis revealed wing shape diversity through (1) the insertion points of the subcosta and R1, resulting in the terminus of the costa exhibiting a trend towards a more apical position on the wing, and (2) the insertion point of the humeral cross vein, resulting in the anterior branch of the media exhibiting a trend toward a more basal position on the wing. Canonical variates analysis of Procrustes distances successfully assigned all exemplar species into their a priori taxonomic groupings. The diversity in wing shape reveals a trend towards decreased length of basal radial cell and increased costalization of anterior wing veins in the evolutionary transition from plesiomorphic prosimuliines to more derived simuliines. The functional significance of these evolutionary transitions is discussed.
... To minimize this, digital images were obtained with a Canon EOS 550D camera, keeping the focal distance constant and with the scapulae oriented with the plane defined by landmarks 3, 4, and 5 parallel to the plane of focus. The distortion caused by projecting all landmarks onto this plane has been shown to have its greatest effect on the acromion (Swiderski, 1993), not considered in our analysis. The coordinates of the landmarks were recorded with tpsDig 2.16 software (Rohlf, 2010) and MorphoJ 1.02 (Klingenberg, 2010) was used to conduct the General Procrustes analysis, a procedure that superimposes all specimens minimizing spatial variability and removing the effects size and orientation of landmark coordinates (Bookstein, 1991; Dryden and Mardia, 1998; Zelditch et al., 2004; Klingenberg, 2010). ...
Many osteological collections from museums and research institutions consist mainly of remains from captive-bred animals. The restrictions related to the space of their enclosures and the nature of its substrate are likely to affect the locomotor and postural behaviors of captive-bred animals, which are widely considered uninformative regarding bone morphology and anatomical adaptations of wild animals, especially so in the case of extant great apes. We made a landmark-based geometric morphometrics analysis of the dorsal side of the scapular bone of both wild-caught and captive-bred great apes to clarify the effect of captivity on the morphology of a bone greatly involved in locomotion. The comparison suggested that captivity did not have a significant effect on the landmark configuration used, neither on average scapular shape nor shape variability, being impossible to distinguish the scapulae of a captive-bred animal from that of a wild-caught one. This indicates that the analyzed scapulae from captive Hominoidea specimens may be used in morphological or taxonomic analyses since they show no atypical morphological traits caused by living conditions in captivity. Am J Phys Anthropol, 2013. © 2013 Wiley Periodicals, Inc.
... The thin-plate spline interpolation function can be used to illustrate this shape difference as a deformed grid (Fig. 2B). (More complete computational details can be found in Bookstein 1991 Bookstein , 1996b; less formal descriptions can be found in Swiderski 1993; Zelditch and Fink 1995.) The full set of partial warps scores can be analyzed in any conventional multivariate analysis to evaluate the effects of hypothesized factors on shape (Bookstein 1996a). ...
The fundamentals of mechanics provide a strong basis for the hypothesis that allometry could be an important constraint on evolutionary changes in shape. Empirical evidence that allometry accounts for sufficient shape variation to be an effective constraint is much weaker. Numerous studies claim to show that most shape variation is correlated with size, but nearly all these studies use morphometric methods that confound size and shape. Consequently, the proportion of the shape variation correlated with size remains unknown. To address this issue, I examined ontogenetic change and adult variation in lower jaws of the fox squirrel, Sciurus niger. Jaw morphologies were quantified using traditional distance measurements and geometric shape variables computed from landmark coordinates. The same analyses were performed on each data set. As expected, analyses of the distance measurements found that allometry accounted for nearly all ontogenetic variation. The same analysis on the coordinate data found that allometry accounts for <50% of the ontogenetic variation in shape. In analyses of adults, allometry explained >50% of the variation in distance measurements but <25% of the variation in shape. These results confirm that analyses of distance measurements confound size and shape and that this can lead to erroneous claims about the importance of allometry.
... In addition to the debate about the use of the sorts of characters most likely to be examined using morphometrics (see above), there has also been much discussion about the suitability of geometric morphometric methodologies for generating phylogenetic character data. Some studies have attempted to use morphometric methods directly to derive new phylogenetic characters (e.g.,Swiderski 1993;Zelditch et al. 1995, 2002) argued that morphometric-based methods that produce sample-referenced results should not be excluded from use in phylogenetic inference as all phylogenetic characters are defined with reference to the sample (for example, a character in an analysis of 3 terminal taxa might have 3 different states, but were the analysis expanded to 5 terminal taxa, the same character might have 3, 4, or 5 states) and that therefore, with care it should also be possible to incorporate such data into a phylogenetic analysis. A number of methods have previously utilized ordination data in defining characters and character states. ...
Despite being the objects of numerous macroevolutionary studies, many of the best-represented constituents of the fossil record-including diverse examples such as foraminifera, brachiopods, and mollusks-have mineralized skeletons with limited discrete characteristics, making morphological phylogenies difficult to construct. In contrast to their paucity of phylogenetic characters, the mineralized structures (tests and shells) of these fossil groups frequently have distinctive shapes that have long proved useful for their classification. The recent introduction of methodologies for including continuous data directly in a phylogenetic analysis has increased the number of available characters, making it possible to produce phylogenies based in whole or part on continuous character data collected from such taxa. Geometric morphometric methods provide tools for accurately characterizing shape variation and can produce quantitative data that can therefore now be included in a phylogenetic matrix in a non-arbitrary manner. Here, the marine gastropod genus Conus is used to evaluate the ability of continuous characters-generated from a geometric morphometric analysis of shell shape-to contribute to a total evidence phylogenetic hypothesis constructed using molecular and morphological data. Furthermore, the ability of continuous characters derived from geometric morphometric analyses to place fossil taxa with limited discrete characters into a phylogeny with their extant relatives was tested by simulating the inclusion of fossil taxa. This was done by removing the molecular partition of individual extant species to produce a "cladistic pseudofossil" with only the geometric morphometric derived characters coded. The phylogenetic position of each cladistic pseudofossil taxon was then compared with its placement in the total evidence tree and a symmetric resampling tree to evaluate the degree to which morphometric characters alone can correctly place simulated fossil species. In 33-45% of the test cases (depending upon the approach used for measuring success), it was possible to place the pseudofossil taxon into the correct regions of the phylogeny using only the morphometric characters. This suggests that the incorporation of extinct Conus taxa into phylogenetic hypotheses will be possible, permitting a wide range of macroevolutionary questions to be addressed within this genus. This methodology also has potential to contribute to phylogenetic reconstructions for other major components of the fossil record that lack numerous discrete characters.
Correlations between morphology and lifestyle of extant taxa are useful for predicting lifestyles of extinct relatives. Here, we infer the locomotor behaviour of Palaeosciurus goti from the middle Oligocene and Palaeosciurus feignouxi from the lower Miocene of France using their femoral morphology and different machine learning methods. We used two ways to operationalize morphology, in the form of a geometric morphometric shape dataset and a multivariate dataset of 11 femoral traits. The predictive models were built and tested using more than half (180) of the extant species of squirrel relatives. Both traditional models such as linear discriminant analysis and more sophisticated models like neural networks had the greatest predictive power. However, the predictive power also depended on the operationalization and the femoral traits used to build the model. We also found that predictive power tended to improve with increasing body size. Contrary to previous suggestions, the older species, P. goti, was most likely arboreal, whereas P. feignouxi was more likely terrestrial. This provides further evidence that arboreality was already the most common locomotor ecology among the earliest squirrels, while a predominantly terrestrial locomotor behaviour evolved shortly afterwards, before the vast establishment of grasslands in Europe.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
Ground squirrels of the genus Marmota are known for their ability to tolerate bitterly cold climates, which they in part accomplish with their exceptional ability to hibernate for as much as eight months a year (Armitage et al., 2003). Most of the 15 living species are associated with montane habitats, and those that are not, like the North American woodchuck (Marmota monax) and the eastern European and central Asian bobak (M. bobak) inhabit regions with strongly seasonal climates and often bitterly cold winters (Armitage, 2000) (Figure 9.1). All marmots construct burrows, which can be more than one metre deep even in comparatively mild climates and as much as seven metres deep in the harsh climates of the Himalayas (Barash, 1989). During the cold phases of the last half of the Quaternary the fossil record demonstrates many marmots inhabited periglacial environments (Zimina and Gerasimov, 1973; Kalthoff, 1999). For these reasons, marmots are sometimes considered to be a quintessentially Quaternary clade, specialists on the cold variable climates that are unique to the past 2.6 million years of Earth’s history. The world in which they originated, however, was very different; a warmer one in which there were no tundra biomes, no glacial-interglacial cycles, and no permanent ice cover in the Northern Hemisphere. In this chapter, we review the fossil and phylogenetic history of marmots, the palaeoenvironments in which they originated, and their relationship to glacial-interglacial cycles to better understand the contexts in which the specializations of this unique clade of rodents arose. The Quaternary, the current geological period, is defined by the onset of permanent ice sheets in the Northern Hemisphere 2.58 million years ago and is by far the coldest period since the extinction of the last non-avian dinosaurs 65 million years ago (Zachos et al., 2001; Gibbard et al., 2010).
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
Background
Understanding airflow through human airways is of importance in drug delivery and development of assisted breathing methods. In this work, we focus on development of a new method to obtain an averaged upper airway geometry from computed tomography (CT) scans of many individuals. This geometry can be used for air flow simulation. We examine the geometry resulting from a data set consisting of 26 airway scans. The methods used to achieve this include nasal cavity segmentation and a deformable template matching procedure. Methods
The method uses CT scans of the nasal cavity of individuals to obtain a segmented mesh, and coronal cross-sections of this segmented mesh are taken. The cross-sections are processed to extract the nasal cavity, and then thinned (‘skeletonized’) representations of the airways are computed. A reference template is then deformed such that it lies on this thinned representation. The average of these deformations is used to obtain the average geometry. Our procedure tolerates a wider variety of nasal cavity geometries than earlier methods. ResultsTo assess the averaging method, key landmark points on each of the input scans as well as the output average geometry are located and compared with one another, showing good agreement. In addition, the cross-sectional area (CSA) profile of the nasal cavities of the input scans and average geometry are also computed, showing that the CSA of the average model falls within the variation of the population. Conclusions
The use of a deformable template method for aligning and averaging the nasal cavity provides an improved, detailed geometry that is unavailable without using deformation.
Morphometric divergence among the skulls of 10 species of plecotine bats (n = 105) was studied using x, y-coordinates of 11 homologous landmarks recorded from the left half dorsal view of each skull. Univariate and multivariate analyses of shape coordinates provided estimates of differences among taxa and between sexes. The differences in size among species were correlated with uniform shape differences. The centroid size to uniform factor allometry was more pronounced longitudinally (i.e., along the midline of the skull) than it was laterally. Significant shape differences among species were also detected in both uniform and non-uniform components. Non-uniform shape variation involved lateral rather than longitudinal displacement of landmarks on the skull. Sexual dimorphism was reflected by centroid size and was seen only in Otonycteris hemprichi, in which females were about 4.4% larger than males. The UPGMA phenograms of Mahalanobis D
2
of shape coordinates and of relative warp scores (in which the uniform shape component had been removed) revealed two consistent phenetic clusters. One was formed by O. hemprichi, with the remaining genera grouping in a second cluster. The relationships among genera in this second cluster varied depending on the phenogram generated. Nevertheless, the UPGMA phenogram derived from Mahalanobis D
2
computed on Bookstein shape coordinates (sexes combined) was entirely congruent with the current systematic hierarchy and phylogenetic hypothesis of the Plecotini sensu stricto recently put forward based on a parsimony analysis of 32 skin and skull characters. In our analysis, the most divergent species group was the monotypic O. hemprichi. A second group was formed by the genus Barbastella. The remaining clusters were composed of species of Corynorhinus; Plecotus; and a cluster containing Idionycteris and Euderma.
A systematic review of Euglandina singleyana was undertaken to thoroughly examine shell morphology, allozyme, and mtDNA variation in specimens of E. singleyana endemic to central Texas. Allozyme similarity ranged from 95% in the most geographically proximal individuals of E. singleyana (Val Verde and Real counties) to 82% between the most distant individuals (Comal and Val Verde counties). DNA sequence similarity, based on a 397 bp partial 16S mtDNA sequence, ranged from 98% in eastern specimens (Comal and Kerr counties) to 95% in individuals from Kerr, Real, and Val Verde counties. Analysis of variation in shell morphology, allozyme similarity, and mtDNA sequences supports the existence of a single, highly variable, widespread species of Euglandina in central Texas. This study also examines the validity of E. immemorata, using morphometric and DNA sequence data and E. exesa, using morphometric data. The morphometric analysis showed that E. immemorata and E. singleyana differ significantly in shape. The current status of E. immemorata and E. exesa are also examined.
The use of quantitative shape data in phylogenetic studies has been challenged on several grounds, the most important being that hypotheses of homology cannot apply to them. Two premises underlie that argument: (1) quantitative data comprise a single homogeneous class, and (2) qualitative and quantitative data are fundamentally different. The first premise is problematic because some morphometric variables are constrained to compare homologous features of organisms, whereas others are not. Those that are so constrained, including traditional measurement data, shape coordinates and partial warps, yield features that can be assessed for their similarities and differences, and the resulting hypotheses of homology can be tested for their congruence with the cladogram. Those variables that are not so constrained, including most outline-based variables as well as multivariate constructs such as principal components and canonical variates, may be useful tools discriminating and sorting taxa by overall similarities in shape, but not for dis-covering characters. The second premise is also problematic because the same logic and methods apply to both qualitative and quantitative data alike. Thus, if care is taken to ensure that morphometric comparisons are framed in terms of homology, there is no barrier to using quantitative variables in phylogenetic studies, especially those produced by geometric morphometrics. Not only are they tools for describing shape differences, they are also tools for understanding the evolutionary history of shape.
Landmarks are discrete anatomical loci that can be recognized as the same point in all specimens in the study. They are often termed “homologous points” because these points can be matched up, one by one, as “the same point” in all individuals in the study. We could restrict the analysis to these points but we might miss a great deal of the morphology if we did, especially when complex curves contain critical information. Additional points that capture information are not discrete anatomical loci (much less homologous); rather than being landmarks these points are “semilandmarks”. The question every researcher must face is what landmarks to use and whether to include semilandmarks at all (and, if so, how they should be sampled).
The new morphometrics, or geometric morphometrics, is a rapidly evolving field. “Morphometrics” has been used to describe a number of fields that study measurements of organisms, and that is why the modifier “new” or “geometric” is necessary to set aside the special subject matter discussed here: the shape of biological organisms as it is studied using as data, point coordinates in two or three dimensions. This includes landmark and outline coordinates. Landmarks are specific points on an organism that correspond in a sensible way over the forms being studied, that is they are homologs; while outline points do not share this notion of homology. The data of morphometrics is now being extended to include tangent directions at coordinates as well (see Bookstein and Green, 1993; Little and Mardia, this volume). Shape is primarily concerned with properties of coordinates that are invariant to scale, location and orientation (see Appendix I, Glossary). The current status of morphometrics together with some future objectives are summarized in a review by Rohlf and Marcus (1993a).
Phenotypic variation within species provides the raw material acted upon by natural selection and other evolutionary mechanisms. As such, the range and variation of morphology within a species can play an important role in determining the tempo of evolution. The range and variance of aspects of cranidial morphology for nine lower Paleozoic trilobites were measured to identify microevolutionary correlates of macroevolutionary patterns. Comparisons were made among sets of homologous landmarks or upon partial warp vector matrices containing similar proportions of variance. Rarefaction and bootstrap analyses helped estimate the effects of sampling. Levels of variance and range of morphology differed considerably within and among time periods. There is no significant temporal decline in the variance or range of morphology, suggesting that developmental or genomic constraints may not have been the primary factors controlling the tempo of trilobite macroevolution. The spatial distribution of cranidial variance differed considerably among taxa, suggesting that a complex set of developmental processes governed the morphogenesis of cranidia within trilobites.
The Cambrian Radiation marks the appearance of representatives of virtually all major skeletonized phyla in the fossil record and clearly represents a fundamental episode in the history of life. Furthermore, the tempo and mode of this evolutionary event have been the subject of intense debate. One area that has been debated is how so many phylum-level body plans can have evolved in such a geologically brief period. Some have argued that there was enhanced morphological flexibility and fewer evolutionary constraints at this time, leading to greater morphological disparity of Early Cambrian faunas. Others have claimed that this is not true because the evolution of most of the animal phyla significantly predates the radiation or because they failed to detect a signature of decreasing morphological disparity through time. At present, the higher-level patterns of diversification during this time period and the relevant implications for Early Cambrian uniqueness are areas of active research interest and debate. Recognizing this debate, we used both a phylogenetic and a morphometric framework to study whether there is a signature of increasing morphological constraint and decreasing flexibility through time within one of the clades that is a significant constituent of the Early Cambrian biota, specifically, the olenelloid trilobites. In this species-rich clade, we found no evidence that morphological changes were becoming either increasingly constrained or less flexible in one of the dominant Early Cambrian metazoan clades as it passed through the Cambrian Radiation.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
An examination of museum material indicated that the lectotypes of Goniobasis christyi Lea, 1862 and G. instabilis Lea, 1862, along with recent collections of putative Elimia interrupta (Haldeman, 1840), represent a new species separate from E. interrupta, sensu stricto. We propose the name E. christyi for the new species, and provide re-descriptions of it and E. interrupta.
Theridomyids were the most diverse and abundant rodents from the Late Eocene to Late Oligocene in Western Europe. As they lived in an archipelago, almost completely (Late Eocene) or partly (Oligocene) isolated from other continental areas, their evolution remained mainly insular, leading to an increase in evolutionary rates. Theridomyids are most often known from isolated teeth, but partial postcranial material is also available. A few subcomplete skeletons of a ricochetal theridomyid (i.e. Issiodoromys) have already been studied, but their locomotor adaptations were probably not restricted to leaping habits, especially in the basal members of the group. The numerous isolated postcranial bones collected in the Paleogene Quercy localities of France and other Western European areas allow us, for the first time, to describe the anatomy of the pivotal bones of the theridomyid locomotor apparatus, in order to enhance our understanding of their specificity and diversity. We performed Factorial Discriminant Analyses (DA) to evaluate theridomyid locomotory behaviour and body shape in comparison with extant taxa. Despite the limited number of taxa for which postcranial data are available, at least four different types of locomotion and postural behaviour can be characterized: (1) the quadrupedal possibly semi-fossorial Suevosciurus; (2) the occasionally bipedal ricochetal Issiodoromys; (3) the scansorial Theridomys bonduelli; and (4) the cursorial Blainvillimys.
The widespread use of mouse models in developmental, behavioural and genetic studies has sparked wider interest in rodent biology as a whole. This book brings together the latest research on rodents to better understand the evolution of both living and extinct members of this fascinating group. Topics analysed include the role of molecular techniques in the determination of robust phylogenetic frameworks; how geometric morphometric methods help quantify and analyse variation in shape; and the role of developmental biology in elucidating the origins of skeletal elements and the teeth. The editors unite these disciplines to present the current state of knowledge in rodent biology, whilst setting the landscape for future research. This book highlights interdisciplinary links across palaeontology, developmental biology, functional morphology, phylogenetics and biomechanics, making it a valuable resource for evolutionary biologists in all fields.
Size and shape are fundamental features of organisms. Ideally, the methods used to describe size and shape must be sensitive enough to detect small differences, and at the same time provide interpretation that is visually satisfying. I compared shape of wings among Eptesicus fuscus, Myotis lucifugus, Pipistrellus hesperas, and Tadarida brasiliensis using three methods of morphometric analysis; principal-components analysis on traditional measures of lengths and areas, principal-components analysis of interlandmark distances, and relative-warp analysis. These species were chosen to test the efficacy of each morphometric analysis at discovering and describing differences in both size and shape. Although principal-components analyses provided similar aggregations of species based on variable loadings, only relative-warps analysis provided clear pictures as to how species differ. The molossid bat, T. brasiliensis, had narrower wings than the vespertilionid bats; this shape was not due to compression of the entire wing, but to a complicated rotation around the fifth digit. The vespertilionid bats were difficult to discern based on wing shape alone, but the warp analysis showed that P. Hesperus and M. lucifugus are more similar in shape of wing than either is to E. fuscus. Each method of analysis of shape has strengths, but relative-warp analysis provided both the power to discriminate among minor differences in shape of species within families, and the graphical capability to display those differences in a visually pleasing way.
A morphometric comparison of scapular shape was conducted between two species of Peromyscus (P. gossypinus and P. floridanus). Earlier findings suggested that scapulae of adult P. floridanus are relatively more horizontally elongate than those of P. gossypinus and were interpreted as being related to differences in frequency of arboreal climbing. However, adult P. floridanus are significantly larger in body size than adult P. gossypinus. Using traditional methods of analysis and tensor-biometrics, a biostatistical approach to landmark data, we examine whether significant differences in scapular shape exist independently of differences in size. Linear measures of adult P. floridanus are consistently and significantly larger than those of adult P. gossypinus, but larger adult P. gossypinus have the same scapular proportions as smaller adult P. floridanus. Tensor analysis confirmed results of traditional methods indicating that the two groups share a common pattern of allometry. This work underscores the importance of an allometric approach to assessing the functional implications of variation in morphology.
To obtain the best surgical results in orthognathic surgery, treatment planning and the evaluation of results should be performed. In these operations it is necessary to provide to the physicians powerful tools able to underline the behaviour of soft tissue. For this reason, considering the improvements provided by the use of 3D scanners, as photogrammetry, in the medical diagnosis this paper proposes a methodology for analysing the facial morphology working with geometrical features. The methodology has been tested over patients affected by malocclusion, in order to analyse the reliability and efficiency of the provided diagnostic results.
The brachiopod genus Sowerbyella is an abundant component of many Ordovician paleocommunities of the eastern United States. Five successive populations from a limited geographic region in central Kentucky were tested for the response of brachial valve size and shape to alterations in paleoenvironmental conditions. The populations span the interval from Chatfieldian to Maysvillian (M5-C3) including the majority of an Ecological-Evolutionary (EE) subunit previously described for brachiopods in this area. A marked diminution in size occurs subsequent to maximum deepening in the M5 sequence, and is persistent for the remainder of the interval sampled. Shape follows a different pattern, with similar changes occurring each time deep-water facies occur in the area. Discriminant analysis shows a clear separation between populations sampled from nearshore and offshore facies along discriminant function 1. End member populations in both nearshore and offshore populations diverge significantly on discriminant function 2 over periods of 6.5 and 3.5 my, respectively, the longer period spanning the majority of the EE subunit. This contrasts with stasis in valve shape in Devonian. brachiopods over an EE subunit of similar duration, but is in accordance with previous findings of less community-level stability in Ordovician EE subunits when compared with their Devonian counterparts.
Growth patterns that lead to sexual dimorphism in adults are not well quantified. We measured 49 skeletal dimensions in male and female Chinchilla lanigera from radiographs of growing individuals taken during 320 days. Measurements for each individual were fit with a nonlinear Gompertz equation to quantify growth patterns. Differences in Gompertz parameters between sexes were compared with a r-test. Most significant differences between sexes in growth and final size were in the pelvic girdle (which formed the birth canal) and viscerocranium. Sexual dimorphism in the viscerocranium may support the hypothesis that differences in use of ecological niche often causes sexual dimorphism where females are larger than males.
Using light microscospy, cross sections of the superior vestibular nerve were compared in 2 tree-dwelling species of squirrels (Sciurus carolinensis and S. niger) and 3 ground-dwelling species (Spermophilus tridecemlineatus, S. mexicanus, and S. variegatus). Fiber number, internal minor diameter of the axon, and axon area were measured for 31,959 fibers taken from 5 males of each species. Significant differences were not found within or among species, suggesting that climbing behaviors are not correlated with these morphologic features of the superior vestibular nerve.
Marmots are of prominent interest for sociobiologists studying mammal societies. They are also a fascinating group on which to test congruence between morphological information and molecular phylogeny and the possible occurrence of homoplasy in the evolution of the sciurid skeleton. To investigate marmot morphological relationships, an analysis of the outlines of the posterior region of the marmot mandible was performed using Elliptic Fourier analysis. Outgroup species belonging to other sciurid genera were also included, and the efficacy of this technique to discriminate taxa based on the morphology of this mandibular region was assessed. The mandible outlines led to a partial separation of the groups under study, but the phylogenetic signal seems to be weak compared to previous studies of the marmot mandible. Indeed, epigenetic influences acting on the posterior region of the mandible, an area of insertion of important masticatory muscles, may be a source of phenotypic variation that can mask the phylogenetic signal. However, interpretations must be made with caution as the posterior region of the mandible is an apparently suitable structure for outline analysis but the poor alignment of the outlines using standard elliptic Fourier methods made the study more complex than expected.
This study tested the hypothesis that developmental heterogeneity in cranial base morphology increases the prevalence of Class III malocclusion and mandibular prognathism in Asians. Thin-plate spline (TPS) graphical analysis of lateral cephalometric radiographs of the cranial base and the upper midface configuration were compared between a European-American group (24 females and 31 males) and four Asian ethnic groups (100 Chinese, 100 Japanese, 100 Korean and 100 Taiwanese; 50 females and 50 males per group) of young adults with clinically acceptable occlusion and facial profiles. Procrustes analysis was performed to identify statistically significant differences in each configuration of landmarks (P < 0.001). The TPS graphical analysis revealed that the greatest differences of Asians were the horizontal compression and vertical expansion in the anterior portion of the cranial base and upper midface region. The most posterior cranial base region also showed horizontal compression between the basion and Bolton point, with forward displacement of the articulare. Facial flatness and anterior displacement of the temporomandibular joint, resulting from a relative retrusion of the nasomaxillary complex and a relative forward position of the mandible were also noted. These features that tend to cause a prognathic mandible and/or retruded midface indicate a morphologic predisposition of Asian populations for Class III malocclusion.
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