Description of the postcranial anatomy of Aulacephalodon baini and its possible relationship with 'Aulacephalodon peavoti'

Abstract

A recent analysis of the postcranial anatomy of Triassic dicynodonts renewed interest in the anatomy of Aulacephalodon. This study focused initially on Aulacephalodon baini as it represents medium to large Permian dicynodonts but also took into account 'Aulacephalodon peavoti'. The postcranial skeletons of A. baini and 'A. peavoti' show several significant differences. The scapula blade of A. baini is more curved than and not as upright as in 'A. peavoti'. A. baini has a rectangular delto-pectoral crest and has a better developed olecranon. In the pelvic girdle the anterior process is higher than the posterior process of the ilium in A. baini and the acetabulum is directed more ventrally. The femoral head is separated from the greater trochanter in A. baini. A comparison also shows that both A. baini and 'A. peavoti' are different from Rhachiocephalus in that the latter has a widely expanded scapula blade and the proximal end of the humerus is wider than the distal. The glenoid is elliptical with a convex surface. Although it could not be conclusively decided what the taxonomic position of 'A. peavoti' is, this study provides information about the postcranial skeleton which could aid its detailed analysis. This study will also assist in clarifying the relationships as well as providing insight into the palaeobiology of these extinct tetrapods.