Claw retraction and protraction in the Carnivora: the cheetah (Acinonyx jubatus) as an atypical felid

Abstract

The cheetah Acinonyx jubatus is the most cursorial felid and has been described as somewhat dog-like in both the shape and the diminished degree of retraction of the claws. In this study we evaluate and investigate the osteological correlates associated with claw retraction in the cheetah through a comparison of the morphology of its middle phalanges with those of other felids and of the wolf Canis lupus. Compared to other felids, the middle phalanges of the cheetah have better-developed grooving of the distal articulatory facets in both the manus and pes, reduced to absent angulation to the distal articulatory facets in the inner and outer digits, less marked asymmetry of the shaft, and a mid-shaft cross-section that is less triangular and more circular. In all of these features, the morphology of the cheetah is intermediate between that of other felids and that of the wolf. The cheetah's distinctive morphology is autapomorphic within Felidae and similarities between the cheetah and the wolf are the result of convergence. Study of an ontogenetic series of specimens of the domestic cat suggests that the morphology of the cheetah can be explained, at least in part, as a product of heterochrony in which the development of the middle phalanx is truncated at an earlier stage than is typical of the adults of other felids. Some of the morphological differences in the middle phalanges of the cheetah can be associated with its distinctive hunting behaviour. The reduced manipulative capabilities of the forelimb associated with the evolution of cursorial adaptations seem to have limited the roles of the forepaws in both the subduing of prey and feeding.