The effect of function, phylogeny, and size, on the morphology of the limb bones in Carnivora was studied. First, the locomotor strategy of non-arboreal mammals on narrow supports was determined, and compared to that of arboreal mammals. To do that, kinematic and coordination variables were studied in the cat (scansorial) and the dog (terrestrial). Arboreal, scansorial and terrestrial species used different strategies to increase stability on narrow supports. However, common features were also observed, such as reducing swing phase duration and using a crouched posture. Secondly, the factors influencing limb morphology were explored and quantified using univariate, bivariate, and multivariate approaches. For the univariate and scaling (bivariate) approaches, a set of 43 variables were measured in the limb bones of 435 specimens belonging to 143 species of Carnivora. The multivariate approach consisted in the study of scapula shape using geometric morphometrics methods. For this analysis, 34 3D-landmarks were digitized on 213 scapulas from 101 carnivoran species. In all those studies, limb bone morphology was determined by the complex interaction of size, phylogenetic history, and function. Conformity to either the elastic or the geometric similarity hypotheses was low. Furthermore, differential scaling was detected in most variables, as well as significant differences between the scaling exponents obtained using traditional regression methods and those using phylogenetically independent contrasts. Both phylogeny and adaptation caused significant deviations from the scaling pattern of the whole order. Locomotor adaptations in the scapula shape of extant carnivorans seemed independent of size or shared ancestry and reflected the particular muscular function associated to different locomotor habits. Finally, a medium-sized, forest-dwelling mammal with mixed adaptations for arboreal and terrestrial habits is supported as the hypothetical ancestor for extant Carnivora.
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