Morphology and locomotor adaptations of the bovid femur in relation to habitat

Extant bovids inhabit a wide diversity of environments that range from forest to savanna and display locomotor patterns that are habitat specific. I report here on an investigation of the linkage between these locomotor patterns and habitat based on a study of the morphology of the bovid femur. Femoral head shape, shaft dimensions, and knee structure are examined and support a statistically significant separation of the different morphological complexes present in bovids from forest, broken cover, and savanna habitats. Morphological differences are primarily related to locomotor patterns as reflected in the degree of cursoriality displayed by bovids in different habitats. Cursorial bovids from savanna environments have laterally expanded femoral heads that act to limit the degree of abduction and axial rotation at the hip, and elliptically shaped distal femora that increase the moment arm of the extensor muscles that cross the knee. Forest bovids have spherically shaped femoral heads. This morphology permits a much higher degree of abduction and axial rotation at the hip and appears to provide greater maneuverability in a vegetationally complex habitat. Bovids living in broken cover environments that fall between the extremes of closed canopy forest and savanna display an intermediate set of femoral characters. This approach to the relationship between habitat and locomotion offers a potentially powerful means with which to examine the interplay between structural form and function in bovid evolution.     

Analyzing ungulate long bones as a tool for habitat reconstruction

The long bones (humerus, radius, metacarpus, femur, tibia, metatarsus) of 51 extant bovid and 7 equid specimens were measured in order to test the hypothesis that they show adaptations to different habitats. We performed factor analyses (FAs) with principal component extraction method and plotted the extracted factors (Fs) in simple scatterplots. The preferred habitats (grassland, forest, mountainous regions) were labeled in the plots, and our results show three clearly separated clusters for F2 vs. F3. According to our interpretation, F1 reflects the body size of the specimens while F2 is most probably reflecting cursorial adaptations. F3 is largely affected by dimensional bone characteristics adapted to maneuver in the environment, and therefore, F3 is somehow linked to habitat. The investigated equids are plotting within the cluster of bovids preferring grassland habitats, which is surprising because of different constructions of the metapodials in perissodactyls and ruminants. Performed linear discriminant analyses (LDAs) are supporting our FA results. This approach combines biometrics with statistics and presents a tool, which easily can be applied helping to identify the paleo-habitat or the paleo-ecology of extinct bovids with implications on fossil localities.     

Evolutionary allometry of lumbar shape in Felidae and Bovidae

As body size increases, so do the biomechanical challenges of terrestrial locomotion. In the appendicular skeleton, increasing size is met with allometry of limb posture and structure, but much less is known about adaptations of the axial skeleton. It has been hypothesized that stabilization of the lumbar region against sagittal bending may be a response to increasing size in running mammals. However, empirical data on lumbar allometry in running mammals are scarce. This study presents quantitative data on allometry of the penultimate lumbar vertebra in two mammal families: Bovidae and Felidae. One hundred and twenty 3D landmarks were collected on the penultimate lumbar vertebra of 34 bovid (N = 123) and 23 felid (N = 93) species. Multivariate phylogenetically informed regressions were computed, and the shape variation associated with increasing size calculated. The influence of locomotor and habitat variables on size‐corrected lumbar shape was tested using phylogenetic multivariate analysis of variance (MANOVAs). Results demonstrate that the scaling patterns in both groups are consistent with the hypothesis of allometric stabilization of the lumbar region, and suggest convergent evolution of allometric responses in distantly related lineages of mammals. However, there was a relatively smaller effect of size in felids than bovids, even when size range disparities were accounted for, suggesting a trade‐off between size and running behaviour. Despite the strong influence of size and phylogeny on lumbar shape, there was no correlation with either habitat or diet within families, though certain specialized taxa (i.e., cheetah) did have divergent morphology.     

牛科(哺乳纲:偶蹄目)动物与生境利用有关的适应形态模式

对广义牛科动物颅后骨骼的多元变量分析揭示了牛科生境利用和体型之间的骨学特征。利用逐步分辨分析方法和一个基于机器学习的决策树方法鉴别了每种生境中牛科动物颅后解剖结构的形态特征。从110个广义牛科动物测量了43个指标进行了这项分析。利用所有主要肢骨测量值和以单根肢骨测量为主的测量值获得的分辨函数和决策树可以完美地区分适应开阔生境、森林和山地的牛科动物(在所有分析中得到了100 %正确的再分类)。由于调整的函数仅涉及到很小的颅后骨骼测量集,这些函数可以应用于研究考古学和古生物学发掘物中保存的不完整标本。这些表征生境利用的生态适应函数与那些用颅齿部性状建立、用于推测牛科动物食物选择的函数结合,具有刻画已灭绝的分类类群的古个体生态学和重建古环境的潜力。我们还分析了多元回归是否较单一因子回归表现出较高的预测能力,并提出了从每一种单根主要肢骨测量的颅后形态变量得到的最好代数函数     

Assessing astragalar morphology and biomechanics in western Palaearctic Bison populations with geometric morphometrics

Having arrived 1.8 Ma ago, bison prevailed in the bovid assemblages of the European subcontinent for more than 1.5 Ma. The current geometric morphometric study outlines a framework of ecomorphological differences among several Bison populations of the western Palaearctic, shown by inferences from the tibial and tarsal joint surfaces of their astragalus. Given the principal biomechanical role of this element in the locomotion mechanism, its anatomical features could be linked to diverse functional aspects. In terms of morphological affinity, it is possible to attribute the studied fossil Bison astragalar material to several morphological trends. Shape variation is not explained by size differences and is possibly associated with an open-close habitat gradient, as indicated by the presence of expanded or compressed astragali, respectively. This intragroup spatial and temporal phenotypic diversity among the examined populations could indicate a biogeographic segregation influenced by regional climatic and landscape heterogeneity in the European territory during Pleistocene. Furthermore, a relation to habitat-specific locomotor ecology could be supported, revealing forms with increased cursoriality, operating in open biomes and closed-country dwellers as well.     

Phylogenetic comparative methods complement discriminant function analysis in ecomorphology

In ecomorphology, Discriminant Function Analysis (DFA) has been used as evidence for the presence of functional links between morphometric variables and ecological categories. Here we conduct simulations of characters containing phylogenetic signal to explore the performance of DFA under a variety of conditions. Characters were simulated using a phylogeny of extant antelope species from known habitats. Characters were modeled with no biomechanical relationship to the habitat category; the only sources of variation were body mass, phylogenetic signal, or random “noise.” DFA on the discriminability of habitat categories was performed using subsets of the simulated characters, and Phylogenetic Generalized Least Squares (PGLS) was performed for each character. Analyses were repeated with randomized habitat assignments. When simulated characters lacked phylogenetic signal and/or habitat assignments were random, <5.6% of DFAs and <8.26% of PGLS analyses were significant. When characters contained phylogenetic signal and actual habitats were used, 33.27 to 45.07% of DFAs and <13.09% of PGLS analyses were significant. False Discovery Rate (FDR) corrections for multiple PGLS analyses reduced the rate of significance to <4.64%. In all cases using actual habitats and characters with phylogenetic signal, correct classification rates of DFAs exceeded random chance. In simulations involving phylogenetic signal in both predictor variables and predicted categories, PGLS with FDR was rarely significant, while DFA often was. In short, DFA offered no indication that differences between categories might be explained by phylogenetic signal, while PGLS did. As such, PGLS provides a valuable tool for testing the functional hypotheses at the heart of ecomorphology. Am J Phys Anthropol 153:663–674, 2014. © 2013 Wiley Periodicals, Inc.     

Biometric study of ruminant carpal bones and implications for phylogenetic relationships

The mammalian Carpus is a complex of several small bones with multiple interactions during walking. Therefore, it is highly probable that different mammalian families developed distinctive constellations in their Carpi, which could be useful for biometric identification of phylogenetic groupings. The carpal bones of nineteen extant ruminant species (nine bovid, nine cervid, and one moschid) have been investigated to search for biometric traits which are diagnostic for the three families. Additionally, we searched for diverging functional adaptations in the carpal constellations. Therefore, measurements have been taken from the five main carpals, which are carrying the body weight. As a sesamoid bone, Os carpi accessorium was excluded. After transformation of the data into their natural logarithms, multivariate methods of factor analyses and discriminant analyses were performed for each bone. Bivariate plots of the factor scores allowed a clear separation of bovids and cervids. The only one species of the Moschidae (Moschus moschiferus) lies closer to the cervids than to the bovids. The grouping is due to phylogenetic relationships and not due to functional differences in the groups or differing habitat preferences. Generally, the carpals of cervids are more slender and higher in contrast to the bulky and flat carpals in bovids. This approach could be used to assign isolated carpal bones found in fossil sites to their ruminant family.     

Combining isotopic and ecomorphological data to refine bovid paleodietary reconstruction: a case study from the Makapansgat Limeworks hominin locality

The relationship between environmental change and hominin evolution remains obscure. For the most part, this stems from the difficulty of reconstructing ancient hominin habitats. Bovids are among the most frequently utilized paleoenvironmental indicators, but little is known about the habitat preferences of extinct taxa. It is generally assumed that fossil bovids both ate the same things and occupied the same habitats as their closest extant relatives. We test the first part of this assumption by reconstructing the diets of seven bovids from Makapansgat Limeworks, South Africa. Since diet and habitat are linked, these reconstructions have implications for our understanding of fossil bovid habitat tolerances. Ecomorphological and stable carbon isotope analyses are employed, allowing us to take advantage of the strengths and overcome the weaknesses of both. In most cases, fossil bovids did have similar diets to their extant relatives, and probably occupied similar habitats. Gazella vanhoepeni and Aepyceros sp., however, were almost exclusive browsers, and not mixed feeders like their living counterparts.     

Evolutionary allometry reveals a shift in selection pressure on male horn size

How selection pressures acting within species interact with developmental constraints to shape macro‐evolutionary patterns of species divergence is still poorly understood. In particular, whether or not sexual selection affects evolutionary allometry, the increase in trait size with body size across species, of secondary sexual characters, remains largely unknown. In this context, bovid horn size is an especially relevant trait to study because horns are present in both sexes, but the intensity of sexual selection acting on them is expected to vary both among species and between sexes. Using a unique data set of sex‐specific horn size and body mass including 91 species of bovids, we compared the evolutionary allometry between horn size and body mass between sexes while accounting for both the intensity of sexual selection and phylogenetic relationship among species. We found a nonlinear evolutionary allometry where the allometric slope decreased with increasing species body mass. This pattern, much more pronounced in males than in females, suggests either that horn size is limited by some constraints in the largest bovids or is no longer the direct target of sexual selection in very large species.     

The Divergence of Echolocation Frequency in Horseshoe Bats: Moth Hearing,Body Size or Habitat?

A phylogenetic approach was used to test three hypotheses regarding the evolution of diversity in the echolocation frequencies used by horseshoe bats (family Rhinolophidae, genus Rhinolophus): 1) Allotonic Frequency Hypothesis (high frequency echolocation in the Rhinolophidae resulted from coevolution with moth hearing); 2) Allometry Hypothesis (echolocation frequency is negatively scaled with body size and evolutionary changes in echolocation frequencies are correlated with changes in body size in the Rhinolophidae); and 3) Foraging Habitat Hypothesis (evolution of echolocation frequency is associated with changes in habitat type). Both discrete and continuous character sets were used for ancestral state reconstructions and for investigating patterns of evolution between frequency and body size, and frequency and habitat type. Contrary to the prediction of the Allotonic Frequency Hypothesis, echolocation frequency in the Rhinolophidae did not increase over time, which would be expected if moth hearing and bat echolocation frequency coevolved. The number of extant species that exhibit calls within moth hearing ranges was not significantly different from the number of species that echolocate outside of moth hearing range. There was also no correlation between changes in frequency and changes in habitat type as predicted by the Foraging Habitat Hypothesis. Instead, the evolution of echolocation frequency within the Rhinolophidae was correlated with changes in body size as predicted by the Allometry Hypothesis.     

Head shape evolution in monitor lizards (Varanus): interactions between extreme size disparity,phylogeny and ecology

Characterizing patterns of observed current variation, and testing hypotheses concerning the potential drivers of this variation, is fundamental to understanding how morphology evolves. Phylogenetic history, size and ecology are all central components driving the evolution of morphological variation, but only recently have methods become available to tease these aspects apart for particular body structures. Extant monitor lizards (Varanus) have radiated into an incredible range of habitats and display the largest body size range of any terrestrial vertebrate genus. Although their body morphology remains remarkably conservative, they have obvious head shape variation. We use two‐dimensional geometric morphometric techniques to characterize the patterns of dorsal head shape variation in 36 species (375 specimens) of varanid, and test how this variation relates to size, phylogenetic history and ecology as represented by habitat. Interspecific head shape disparity is strongly allometric. Once size effects are removed, principal component analysis shows that most shape variation relates to changes in the snout and head width. Size‐corrected head shape variation has strong phylogenetic signal at a broad level, but habitat use is predictive of shape disparity within phylogenetic lineages. Size often explains shape disparity among organisms; however, the ability to separate size and shape variation using geometric morphometrics has enabled the identification of phylogenetic history and habitat as additional key factors contributing to the evolution of head shape disparity among varanid lizards.     

Size matters for lice on birds: Coevolutionary allometry of host and parasite body size

Body size is one of the most fundamental characteristics of all organisms. It influences physiology, morphology, behavior, and even interspecific interactions such as those between parasites and their hosts. Host body size influences the magnitude and variability of parasite size according to Harrison's rule (HR: positive relationship between host and parasite body sizes) and Poulin's Increasing Variance Hypothesis (PIVH: positive relationship between host body size and the variability of parasite body size). We analyzed parasite–host body size allometry for 581 species of avian lice (～15% of known diversity) and their hosts. We applied phylogenetic generalized least squares (PGLS) methods to account for phylogenetic nonindependence controlling for host and parasite phylogenies separately and variance heterogeneity. We tested HR and PIVH for the major families of avian lice (Ricinidae, Menoponidae, Philopteridae), and for distinct ecological guilds within Philopteridae. Our data indicate that most families and guilds of avian lice follow both HR and PIVH; however, ricinids did not follow PIVH and the “body lice” guild of philopterid lice did not follow HR or PIVH. We discuss mathematical and ecological factors that may be responsible for these patterns, and we discuss the potential pervasiveness of these relationships among all parasites on Earth.     

牛科(哺乳纲:偶蹄目)动物与食物有关的适应形态模式

利用逐步分辨分析方法（Stepwise discriminant analysis,SCDA）检测了广义牛科动物的颅齿部结构,这些结构特征可以作为采食行为生态适应特征。在本研究中,测量了72种广义牛科动物的28个颅齿部结构。逐步分辨分析方法得出了6种采食方式适应类型：一般粗食者、新鲜禾草粗食者、开阔生境混合型采食者、精食者、郁闭生境混合型采食者、食果者。用103个标本检测了分辨指标的预测能力,所用标本为缺损标本,大多数缺少一项或多项结构。从这些标本获得的分辨函数的平均预测能力为94％,比用72种广义牛科动物标本建立的分辨函数的平均预测能力（98％）低一些。从一个颅齿部结构小样本建立的分辨函数可以用于考古发掘物中不完整标本的研究。这些指标与用颅下结构测量建立的运动能力和生境选择的指标相结合,可以推断古牛科动物的个体生态学以及古环境重建。     

Scaling of cursoriality in mammals

Data on limb bone lengths from 64 mammalian species were combined with data on 114 bovid species (Scott, '79) to assess the scaling of limb lengths and proportions in mammals ranging from 0.002 to 364 kg. We analyzed log-transformed data using both reduced major axis and least-squares regression to focus on the distribution across mammals of two key traits—limb length and metatarsal/femur ratio—associated with cursorial adaptation. The total lengths of both fore and hindlimbs scale in a manner very close to the M^0.33 predicted by geometric similarity. Thus the relative limb lengths of large mammals, including bovids, generally regarded among the most cursorial of mammals, are very similar to those of the rodents and insectivores in this sample. Metatarsal/femur ratio also shows little change with changing mass, although bovids tend to have relatively longer metapodials than do other families in the sample. We argue that many of the remaining morphological traits associated with cursoriality (e.g., reduction in joint mobility and number of distal limb bone elements) promote cursoriality only at large body sizes. These results lead us to question the general perception that cursoriality is most widespread among large mammals. We also suggest that discussions of cursoriality should focus explicitly on the two partially independent aspects of performance that are otherwise confounded under this general term—speed and the ability to cover substantial distance. © 1993 Wiley-Liss, Inc.     

Using functional traits and phylogeny to understand local extinction risk in dragonflies and damselflies (Odonata)

Understanding the risk of local extinction of a species is vital in conservation biology, especially now when anthropogenic disturbances and global warming are severely changing natural habitats. Local extinction risk depends on species traits, such as its geographical range size, fresh body mass, dispersal ability, length of flying period, life history variation, and how specialized it is regarding its breeding habitat. We used a phylogenetic approach because closely related species are not independent observations in the statistical tests. Our field data contained the local extinction risk of 31 odonate (dragonflies and damselflies) species from Central Finland. Species relatedness (i.e., phylogenetic signal) did not affect local extinction risk, length of flying period, nor the geographical range size of a species. However, we found that closely related species were similar in hind wing length, length of larval period, and habitat of larvae. Both phylogenetically corrected (PGLS) and uncorrected (GLM) analysis indicated that the geographical range size of species was negatively related to local extinction risk. Contrary to expectations, habitat specialist species did not have higher local extinction rates than habitat generalist species nor was it affected by the relatedness of species. As predicted, species’ long larval period increased, and long wings decreased the local extinction risk when evolutionary relatedness was controlled. Our results suggest that a relatively narrow geographical range size is an accurate estimate for a local extinction risk of an odonate species, but the species with long life history and large habitat niche width of adults increased local extinction risk. Because the results were so similar between PGLS and GLM methods, it seems that using a phylogenetic approach does not improve predicting local extinctions.     

Astragali of Pakicetidae and other early-to-middle Eocene archaeocetes (Mammalia,Cetacea) of Pakistan: locomotion and habitat in the initial stages of whale evolution

Richard Dehm and colleagues of the Bayerische Staatssammlung für Paläontologie und Geologie in Munich made an important collection of early-to-middle Eocene mammals at Ganda Kas in Pakistan during the winter of 1955/56. The genera and species Ichthyolestes pinfoldi and Gandakasia potens were named from this collection. Both are now recognized as early and primitive archaeocete cetaceans. In addition, Dehm’s group collected 16 complete or partial astragali of archaeocetes that were misidentified as artiodactyls. These bring the total number of archaeocete astragali known from Ganda Kas to 28. They separate clearly into four species distinguished by size: from smallest to largest Ichthyolestes pinfoldi Dehm and Oettingen-Spielberg, Pakicetus attocki (West), Gandakasia potens Dehm and Oettingen-Spielberg, and Ambulocetus natans Thewissen et al. Ganda Kas artiodactyls are smaller and rare in comparison. Ichthyolestes and Pakicetus are pakicetid archaeocetes, Gandakasia is presently indeterminate to family, and Ambulocetus is an ambulocetid. Tooth size and astragalus size are highly correlated, corroborating reference of astragali to the first three archaeocete taxa based on teeth. Multivariate morphometric comparison (Auto3Dgm) shows that pakicetid astragali overlap almost completely in shape with those of early artiodactyls. Middle Eocene protocetid astragali are divergent from both. Retention of an astragalus indistinguishable from that of artiodactyls shows that pakicetids are closely related to artiodactyls phylogenetically, but does not make Ichthyolestes and Pakicetus terrestrial or cursorial. Other skeletal elements and bone microstructure indicate that pakicetids were semiaquatic like later protocetids. Tropical riverine and marginal marine facies of the Kuldana Formation are likely habitats for initial stages of the transition from terrestrial artiodactyls to semiaquatic and fully aquatic archaeocetes.     

On the selection of phylogenetic eigenvectors for ecological analyses

Among the statistical methods available to control for phylogenetic autocorrelation in ecological data, those based on eigenfunction analysis of the phylogenetic distance matrix among the species are becoming increasingly important tools. Here, we evaluate a range of criteria to select eigenvectors extracted from a phylogenetic distance matrix (using phylogenetic eigenvector regression, PVR) that can be used to measure the level of phylogenetic signal in ecological data and to study correlated evolution. We used a principal coordinate analysis to represent the phylogenetic relationships among 209 species of Carnivora by a series of eigenvectors, which were then used to model log‐transformed body size. We first conducted a series of PVRs in which we increased the number of eigenvectors from 1 to 70, following the sequence of their associated eigenvalues. Second, we also investigated three non‐sequential approaches based on the selection of 1) eigenvectors significantly correlated with body size, 2) eigenvectors selected by a standard stepwise algorithm, and 3) the combination of eigenvectors that minimizes the residual phylogenetic autocorrelation. We mapped the mean specific component of body size to evaluate how these selection criteria affect the interpretation of non‐phylogenetic signal in Bergmann's rule. For comparison, the same patterns were analyzed using autoregressive model (ARM) and phylogenetic generalized least‐squares (PGLS). Despite the robustness of PVR to the specific approaches used to select eigenvectors, using a relatively small number of eigenvectors may be insufficient to control phylogenetic autocorrelation, leading to flawed conclusions about patterns and processes. The method that minimizes residual autocorrelation seems to be the best choice according to different criteria. Thus, our analyses show that, when the best criterion is used to control phylogenetic structure, PVR can be a valuable tool for testing hypotheses related to heritability at the species level, phylogenetic niche conservatism and correlated evolution between ecological traits.     

Locomotor correlates of the scapholunar of living and extinct carnivorans

The relationship of carpal morphology to ecology and habitat is under studied in carnivorans and more generally in mammals. Here, we use 3D-scanning techniques to assess the usefulness of a carpal bone, the scapholunar, in carnivorans to reflect ecology and habitat, and to reconstruct the ecology of five extinct carnivorans from two fossil sites: Rancho La Brea and Natural Trap Cave. We 3D-scanned scapholunars and measured articular surface areas and angles between articular facets using GeoMagic and Rhino 3D-software. We analyzed the difference in these metrics using multivariate analysis of variance and discriminant function analysis. Results show that the scapholunar reflects ecological signal, with clear groupings of cursorial carnivorans and grappling/climbing carnivorans; however, phylogenetic signal was also present in the results with hyaenids, canids, and large felids in distinct morphospaces. Extinct species Miracinonyx trumani (American cheetah) and Smilodon fatalis (sabertooth cat) showed surprising results with M. trumani grouping with pantherines instead of Acinonyx or Puma, suggesting it runs but still retains the ability to grapple prey. S. fatalis groups with pantherines, but also shows some unique adaptations, suggesting it had a different range of wrist motion than living cats. Overall, the scapholunar is a good indicator of ecology and functional morphology and can be another tool to use in modern and fossil carnivorans to reconstruct extinct ecologies and locomotor behaviors.     

Functional aspects and ecological implications in Pleistocene endemic herbivores of Mediterranean Islands

The endemic herbivores of Pleistocene Mediterranean Islands, in their processes of adaptation and speciation, show two main tendencies: size variations, widely described in the case of size reduction, and morphological and functional variations, mainly concerning the distal segment of limbs. In the so‐called pachyderms (elephants and hippos) adaptive morphologies are added to variations due to size reduction and point out a cursorial attitude. The endemic insular cervids show perhaps less remarkable functional modifications, but these modifications demonstrate that each form acquire characteristic adaptations, in function of their ecological niche. The modifications of endemic bovids are less known with exception of the dwarf balearic bovids, in which the evolutive process prouced remarkable cranial, dental and limb modifications.     

Evolutionary allometry of the thoracolumbar centra in felids and bovids

Mammals have evolved a remarkable range of body sizes, yet their overall body plan remains unaltered. One challenge of evolutionary biology is to understand the mechanisms by which this size diversity is achieved, and how the mechanical challenges associated with changing body size are overcome. Despite the importance of the axial skeleton in body support and locomotion, and much interest in the allometry of the appendicular skeleton, little is known about vertebral allometry outside primates. This study compares evolutionary allometry of the thoracolumbar centra in two families of quadrupedal running mammals: Felidae and Bovidae. I test the hypothesis that, as size increases, the thoracolumbar region will resist increasing loads by becoming a) craniocaudally shorter, and b) larger in cross‐sectional area, particularly in the sagittal plane. Length, width, and height of the thoracolumbar centra of 23 felid and 34 bovid species were taken. Thoracic, prediaphragmatic, lumbar, and postdiaphragmatic lengths were calculated, and diameters were compared at three equivalent positions: the midthoracic, the diaphragmatic and the midlumbar vertebra. Allometric slopes were calculated using a reduced major axis regression, on both raw and independent contrasts data. Slopes and elevations were compared using an ANCOVA. As size increases the thoracolumbar centra become more robust, showing preferential reinforcement in the sagittal plane. There was less allometric shortening of the thoracic than the lumbar region, perhaps reflecting constraints due to its connection with the respiratory apparatus. The thoracic region was more robust in bovids than felids, whereas the lumbar region was longer and more robust in felids than bovids. Elongation of lumbar centra increases the outlever of sagittal bending at intervertebral joints, increasing the total pelvic displacement during dorsomobile running. Both locomotor specializations and functional regionalization of the axial skeleton appear to have influenced its response to increasing size. J. Morphol. 276:818–831, 2015. © 2015 Wiley Periodicals, Inc.