Evolution of scapula size and shape in Carnivora: locomotor habits and differential shape scaling

The effect of size, phylogeny, and locomotor habit, on shape was tested in 213 scapulas from 101 carnivoran species using 3D geometric morphometric methods. The sampled species spanned the whole size range and locomotor patterns in Carnivora. The results of the present study indicate that, in this order, scapula shape responds to the complex interaction of allometric, phylogenetic, and functional effects. Furthermore, evidence for differential scaling in the shape of the carnivoran scapula was found, which might be related to scaling differences among carnivoran families. Additionally, most allometric shape variation in the carnivoran scapula was related to size changes along phyletic lines. Locomotor-related shape differences were assessed using canonical variate analysis. Most locomotor habits could be significantly separated from each other based on scapula shape, although high misclassification rates were obtained when comparing semiarboreal and semifossorial carnivorans to other locomotor types. Locomotor indicators in the scapula shape of extant carnivorans seemed independent of size or shared ancestry and could be related to muscular function. These locomotor indicators were then used to infer the locomotor habits of several internal nodes of the carnivoran phylogeny, whose scapular size and shape was reconstructed using weighted square-change parsimony. According to scapula size and shape, the carnivoran ancestor was a medium-sized scansorial animal (i.e., it spent most of its time on the ground, but was a good climber).