| Abstract: | A new reconstruction of the tarsus of Stenaulorhynchus stockleyi differs from that previously offered by von Huene (1938) and Schaeffer (1941), and leads to a revaluation of the tarsi of other rhynchosaurs and rhynchocephalians. The tarsi of the rhynchosaurs Stenaulorhynchus, Scaphonyx, Cephalonia, Rhynchosaurus, Hyperodapedon, Howesia and Mesosuchus appear to comprise a proximal row of three bones (tibiale, intermedium, and fibulare) and a distal row of three bones associated with metatarsals–4. The metatarsals increase in length but decrease in thickness from the first to fourth, and the fifth is "hooked". The first metatarsal of Stenaulorhynchus, Scaphonyx , and Rhynchosaurus is unusually short. Among the remaining rhynchocephalians, the tarsi of claraziids and pleurosaurids are simplified in accord with aquatic habits involving the use of the limbs as paddles, and those of sphenodontids and Sapheosaurus are alike in the following respects. An astragalus (intermedium+tibiale+ centrale) and calcaneum (fibulare), or a single conjoined bone, occupy the proximal row of the tarsus and the distal row comprises four (first to fourth), three (second to fourth), or but two (third and fourth) bones; the fourth is the largest. The metatarsals increase in length from first to fourth but do not decrease in thickness. In both rhynchosaurian and spheno-dontid types tarsal movement is largely mesotarsal, a condition derived from their eosuchian ancestors and not independently developed as Schaeffer (1941) has thought. The specialization of the sphenodontid tarsus parallels that seen in lizards which have the same eosuchian ancestry. |
