Differing limb functions and their potential influence upon the diversification of the mustelid hindlimb skeleton

Though form-function relationships of the mammalian locomotor system have been investigated for over a century, recent models of trait evolution have hitherto been seldom used to identify likely evolutionary processes underlying the locomotor system’s morphological diversity. Using mustelids, an ecologically diverse carnivoran lineage, I investigated whether variation in hindlimb skeletal morphology functionally coincides with climbing, digging, swimming, and generalized locomotor habits by using 15 linear traits of the femur, tibia, fibula, calcaneum, and metatarsal III across 44 species in a principal components analysis. I subsequently fit different models of Brownian motion and adaptive trait diversification individually to each trait. Climbing, digging, and swimming mustelids occupy distinct regions of phenotypic space characterized by differences in bone robustness. Models of adaptive and neutral evolution are, respectively, the best fits for long bone lengths and muscle in-levers...