Article: Anatomy and relationships of the pareiasaur Pareiasuchus nasicornis from the Upper Permian of Zambia
M. S. Y. Lee, C. E. Gow and J. W. Kitching
A well-preserved and newly prepared skull has enabled a critical re-evaluation 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 described for the first time. Most elements typical of basal amniotes are present; however, the postparietal is a single median ossification, the tabular is absent, and a ' supernumerary element' (possibly a modified cervical osteoderm) is present. Among the better-known pareiasaur taxa, Pareiasuchus appears to be most closely related to Pareiasaurus, Scutosaurus and Elginia - other forms with highly elaborate cranial ornament. Autapomorphies of Pareiasuchus include: forked distal end of humerus; and proximal end of femoral shaft greatly bent preaxially. Autapomorphies of P. nasicornis include: posteriorly projecting cheek flanges; medially inflected premaxillary and maxillary teeth; and a discrete ossification over each external naris. The specimen demonstrates that many features previously suggested to be unique (amongst basal amniotes) to procolophonoids and turtles also characterize pareiasaurs: for instance, wide antorbital buttress formed by the prefrontal and palatine; short cultriform process; and medially enclosed adductor fossa. P. nasicornis was a large terrestrial herbivore, as evidenced by the crenulated, labiolingually flattened tooth crowns, depressed jaw articulation, 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.