Postcranial remains of Fabrosauridae (Reptilia: Ornithischia) from the Stormberg of southern Africa

摘要

The postcranial skeletons of three fabrosaurids from the upper Elliot Formation "Red Beds" of the Stormberg Group in southern Africa are described. The material demonstrates details of fabrosaurid anatomy previously unknown, particularly a short, deep prepubic process which is undoubtedly primitive for the Ornithischia. Besides the short prepubis, fabrosaurids are characterized by 1) a reduced manus; 2) an ilium having a lateral extension of the supra-acetabular margin and a deep nearly vertical brevis shelf; and 3) an elongated hindlimb. Postcranial morphology excludes the fabrosaurids from the ancestry of the contemporaneous heterodontosaurids. Neither can the fabrosaurids be considered ancestral to the 'juvenile scelidosaurid' (BMNH R6704) as has been suggested. On the contrary, the 'scelidosaurid' is more primitive in structure than fabrosaurids. The assignment of Nanosaurus agilis Marsh to the Fabrosauridae is not substantiated after morphological comparisons between the postcranial material of both. The taxonomic status of Scutellosaurus lawleri is regarded as uncertain. The fabrosaurids are more similar to the Morrison Formation camptosaurids, than to Hypsilophodon. Finally, it is argued that ornithopods were not a basal stock for the phylogenesis of non-ornithopods but represent an independent radiation comparable to the other ornithischian suborders. The fabrosaurids were an early development of the ornithopod radiation itself.