Funny Bones: Ecomorphology of the Bovid Distal Humerus and its Paleontological Implications

Abstract

When seeking to understand early human evolution, it is fundamental to understand the ecology of the environment in which those early humans lived. This is an important overlap between the fields of anthropology and palaeontology, and here I take an ecomorphological approach involving the study of variation in bone morphology as a proxy for ecology in bovids. The family Bovidae (Mammalia: Artiodactyla) dominated ecosystems at the time of early human (Homo sapiens) evolution, and continue to in many areas today, as well as frequently having been domesticated throughout human history. For these reasons, bovids provide an excellent study group for this research. The main aim of this project is to develop the bovid distal humerus as an ecological proxy using 3D geometric morphometrics on 116 scans of extant bovid species, representing 11 of the approximately 16 extant bovid tribes, and 40% of known extant species. The humerus is particularly informative due to its extensive roles in weight-bearing and forelimb use. This study focuses on the distal humerus (the elbow articulation) as this section of bone is dense and frequently preserved in the bovid fossil record, and additionally a great many attachment and origin sites for muscles involved in lower forelimb movement are concentrated at the distal humerus. I find evidence that aspects of distal humerus morphology have evolved convergently across bovids, relating to body mass and habitat preference, and that distal humerus morphology can be a proxy to infer such information in bovids. This information can be utilized to understand the ecology of extinct bovids, and in the final part of this project I apply this to the case of the unusual Pleistocene bovid Rusingoryx atopocranion, which is known to have been hunted by early humans. The results indicate that the unusual distal humerus morphology observed in Rusingoryx is directly related to the animal being highly adapted for cursoriality on the hard, flat terrain of the Kenyan shores of Lake Victoria in the Pleistocene.