Very interesting are the modifications of the wrist and hand in the marine Crocodilia (Fig. 150). But two carpals remain, corresponding to the elongated ossified bones of the terrestrial forms; the first of them, the supposed radiale, is very broad and flat.
Fig. 150. Geosaurus (Thalattosuchia). Elongate left hind leg, and paddle-like left front leg. After Fraas.
The carpus and hand of the strictly aquatic or marine reptiles are so like the ankle and foot that they may be discussed together (p. 193).
Tarsus
The earliest known tarsus is that of Eosauravus (Fig. 151 b), presumably a cotylosaur reptile, though the skull is not known, from the middle Pennsylvanian. It has but two bones in the proximal row, corresponding quite to the astragalus and calcaneum of mammals and the typical reptiles. Beyond these, six, and only six, bones are visible, five of which are undoubted tarsalia; one may be a centrale. The whole number, eight, was the most known in any reptile until recently. Nine bones are present in the tarsus of Ophiacodon (Fig. 152), from the uppermost Pennsylvanian or basal Permian of New Mexico: two in the proximal row, the astragalus and calcaneum, two centralia in the middle row on the tibial side; and five tarsaha in the distal row, one corresponding to each metatarsal. Since this discovery two centralia have also been found by Watson in the genus Broomia (Fig. 137 d), from the Permian of South Africa; and probably also two in the cotylosaurian genus Labidosaurus. The second
