THE TARSUS OF ERYTHROSUCHID ARCHOSAURS, AND IMPLICATIONS FOR EARLY DIAPSID PHYLOGENY

The morphology of the erythrosuchid ankle joint is reassessed. Two spe cimens, recently thought to have been incorrectly referred to Erythros uchus africanus, are shown without doubt to belong to this taxon. Furt hermore, the morphology is essentially similar to that of other early archosaurs. The tarsus of Erythrosuchus is poorly ossified and consist s of a calcaneum, astragalus, and two distal tarsals. The calcanea of Erythrosuchus, Vjushkovia triplicostata, and Shansisuchus shansisuchus are all similar in being dorsoventrally compressed, possessing a late ral tuber, and lacking a perforating foramen. The astragalus of V. tri plicostata is currently unknown. The astragalus of Shansisuchus is app arently unique in form. The erythrosuchid pes is therefore more derive d than has been recently proposed. The tarsal morphology of several ot her archosauromorph taxa is reviewed and many details are found to be at variance with the literature. The plesiomorphic condition for the A rchosauromorpha consists of four distal tarsals and a proximal row of three elements; two of which articulate with the tibia. These proximal elements are interpreted as the astragalus, calcaneum, and a centrale , and the same pattern is retained in the earliest archosaurs. This re assessed tarsal morphology has implications for the homology of the ce ntrale and reconstruction of early diapsid phylogeny. (C) 1996 The Lin nean Society of London