Multiple exostoses and an osteochondroma in a Pliocene canid from Langebaanweg ‘E’ Quarry (South Africa)

Abstract

Langebaanweg is a Mio-Pliocene locality located on the West Coast of South Africa. It is renowned for its rich diversity of both terrestrial and marine vertebrate fossils. Several carnivorans have been identified from this site, amongst which is the recently described jackal-like canid, Eucyon khoikhoi. One of the skeletons assigned to E. khoikhoi exhibits anatomical deformities on several bones of the skeleton. Here, we use multiple methodologies (anatomical descriptions, CT scanning and histology) to investigate the bony overgrowths or exostoses evident in the radius, and we compare these findings with those of a radius from a healthy individual of the same species from Langebaanweg. Our results show that anatomical observations are important for first level observation of the pathology, but that micro-CT scanning permits a more precise assessment of how the pathology affected the internal organization of the bone, both periosteally and endosteally. This methodology permitted us to diagnose the tumors as benign rather than cancerous. Our observations of calcified cartilage in the histological thin sections in the region of the exostosis allowed us to further diagnose the exostosis as an osteochondroma. This study has demonstrated the usefulness of applying multiple techniques to characterize and diagnose pathological bony growths in a fossil canivoran. We have also demonstrated the usefulness of histological studies in permitting a more refined diagnosis of the exostosis as an osteochondroma.