ANATOMY AND RELATIONSHIPS OF THE PAREIASAUR PAREIASUCHUS-NASICORNIS FROM THE UPPER PERMIAN-OF-ZAMBIA

A well-preserved and newly prepared skull has enabled a critical re-ev aluation of the genus Pareiasuchus (Reptilia; Pareiasauridae) and the species Pareiasuchus nasicornis. The skull is heavily ossified, deeply sculptured, akinetic and anapsid. The skull roof sutures are describe d for the first time. Most elements typical of basal amniotes are pres ent; however, the postparietal is a single median ossification, the ta bular is absent, and a 'supernumerary element' (possibly a modified ce rvical osteoderm) is present. Among the better-known pareiasaur taxa, Pareiasuchus appears to be most closely related to Pareiasaurus, Scuto saurus and Elginia - other forms with highly elaborate cranial ornamen t. Autapomorphies of Pareiasuchus include: forked distal end of humeru s; and proximal end of femoral shaft greatly bent preaxially. Autapomo rphies of P. nasicornis include: posteriorly projecting cheek flanges; medially inflected premaxillary and maxillary teeth; and a discrete o ssification over each external naris. The specimen demonstrates that m any features previously suggested to be unique (amongst basal amniotes ) to procolophonoids and turtles also characterize pareiasaurs: for in stance, wide antorbital buttress formed by the prefrontal and palatine ; short cultriform process; and medially enclosed adductor fossa. P. n asicornis was a large terrestrial herbivore, as evidenced by the crenu lated, labiolingually flattened tooth crowns, depressed jaw articulati on, small gape, heavy jaws, reduced transverse flange of the pterygoid , and heavy, akinetic skull. The distinctive cheek flange and angular boss were probably defensive structures.