The vertebrate fauna of the Upper Permian of Niger—III, morphology and ontogeny of the hindlimb of Moradisaurus grandis (Reptilia, Captorhinidae)

ABSTRACT

We describe hindlimb elements of the large captorhinid Moradisaurus grandis (Reptilia: Captorhinidae) recently collected from the Upper Permian Moradi Formation of north-central Niger. This description is based primarily on an associated partial skeleton comprising a hemimandible, vertebral column, and partial left and nearly complete right hindlimb. Additionally, we report on a well-preserved, articulated, and essentially complete juvenile pes that provides important information on the ontogeny of the captorhinid tarsus. The hindlimb of Moradisaurus is stout and more massively built than in any other known captorhinid. The femur displays several features interpreted as adaptations to the demands of large body size, and the tibia and fibula have short, wide shafts and hypertrophied condyles and epicondyles. The astragalus is very derived, possessing two accessory ossifications and a relatively horizontal tibial articulation, indicating that the tibia was held more vertically than in other captorhinids. The calcaneum is co-ossified with distal tarsal five. The juvenile pes indicates that the captorhinid centrale arose from the fusion of two ossification centers, and that the captorhinid astragalus arose from the fusion of at least three ossification centers.