Understanding morphological variation of the elbow joint in the Ursidae: Insights from 3D Geometric Morphometrics

Variation in the skeletal morphology within the Carnivora has long been demonstrated as a predictor of a species’ ecological habits. The elbow joint in particular is a clear indicator of predation strategy[1]. Members of the Ursidae display significant diversity of locomotory and foraging habits and fall into three distinct subfamilies, thus proving to be an excellent group in which to study the interplay of ecology and phylogeny on elbow joint morphology. Previous work using 2D Geometric Morphometrics has revealed an effect of both phylogeny and ecology yet did not discriminate between all locomotory groups[2]. However, given the complexity of the elbow joint, 2D Geometric Morphometrics may be insufficient to fully capture the complexity of this feature. A 3D Geometric Morphometric approach was applied to thirty Ursid specimens with the aim of exploring how ecology and phylogeny can explain morphological variation at the elbow joint. Morphological variation was a good predictor of both locomotory and foraging habits. However, the relative importance of these two ecological factors cannot be easily separated. Furthermore, phylogeny also contributes to variation in the shape of the elbow joint although to a lesser extent than the above-mentioned ecological factors. In contrast to previous work, we demonstrate morphological differences between all ursid groups based on locomotory and foraging habits. This confirms elbow joint morphology as both a clear adaptation to the many ecological niches the Ursidae has occupied since its Oligocene emergence and an excellent illustration of the adaptive radiation of mammalian carnivores throughout the Cenozoic. 1. Andersson, K. I. (2004) ‘Elbow‐joint morphology as a guide to forearm function and foraging behaviour in mammalian carnivores-’, Zoological Journal of the Linnean Society, 142, pp. 91–104. https://doi.org/10.1111/j.1096-3642.2004.00129.x 2. Meloro, C. and Marques de Oliveira, A. (2017) ‘Elbow Joint Geometry in Bears (Ursidae, Carnivora): a Tool to Infer Paleobiology and Functional Adaptations of Quaternary Fossils’, Journal of Mammalian Evolution. Journal of Mammalian Evolution, pp. 1–14. doi: 10.1007/s10914-017-9413-x