Quantifying morphological adaptations using direct measurements: The carnivoran appendicular skeleton as a case study

Here, I study whether locomotor adaptations can be detected in limb bones using a univariate approach, and whether those results are affected by size and/or shared evolutionary history. Ultimately, it tests whether classical papers on locomotor adaptations should be trusted. To do that, I analyzed the effect of several factors (size, taxonomic group, and locomotor habit) on limb bone morphology using a set of 43 measurements of the scapula, long bones, and calcaneus, of 435 specimens belonging to 143 carnivoran species. Size was the main factor affecting limb morphology. Size-corrected analyses revealed artifactual differences between various locomotion-related categories in the analyses of raw data. Additionally, several between-group differences were new to the size-corrected analyses, suggesting that they were masked by the size-effect. Phylogeny had also an important effect, although it only became apparent after removing the effect of size, probably due to the strong covariation of both factors. Regarding locomotor adaptations, locomotor type was used to represent locomotor specialization, and utilized habitat as an indicator of the capacity to adopt different modes of locomotion (running, swimming, climbing, and digging) and thus maximize resource exploitation by being capable of navigating all the substrates in the habitat they use. Locomotor type produced better results than utilized habitat, suggesting that carnivorans use locomotor specialization to minimize locomotion costs. The characteristic limb bone morphology for each locomotor type studied is described, including several adaptations and trends that are novel to the present study. Finally, the results presented here support the hypothesis of a "viverrid-like", forest-dwelling carnivoran ancestor, either arboreal or terrestrial.