Still there? Late Campanian sphenodontids from Patagonia

SEBASTIÁN APESTEGUÍA

La Plata

Jornada; XX Jornadas Argentinas de Paleontologia de Vertebrados; 2004

Museo de La Plata

As evidenced by their fossil record, sphenodontids survived in Gondwana much more than in Laurasia, where the diversification of lizards probably restricted their adaptive zones and drove them to extinction after Early Cretaceous times. The discovery of Priosphenodon informs us that at least eilenodontine sphenodontids survived in Patagonia until “Middle” Cretaceous times. Careful examination of Los Alamitos collections at MACN provided remains of additional sphenodontids. The most conspicuous remains is a large left lower jaw belonging to a new non-eilenodontine, but square-toothed, sphenodontian. Teeth are separated each other, striated in the lingual side, square-based and slightly compressed laterally. Labial side shows deep marks of maxillary teeth, these being not well-defined, but elongated, thus demonstrating relatively long propalinal movements. Four additional teeth are preserved and the bases of two severely eroded hatchling teeth. The complete jaw must have been about 11 cm long which is large for a sphenodontian, and the dentary is curved, especially in the dorsal border, as in Clevosaurus. Also as in the latter, the teeth are restricted to the back of the jaw, with a long completely edentate middle and anterior region that resembles Triassic and Jurassic ‘clevosaurs’. This feature, however, is also present in some Opisthias (LACM 120467, 120542). The phylogenetic position of this specimen is still uncertain, but its features open the possibility of an unknown radiation of basal opisthodontians, unusual sphenodontines or surviving clevosaurs.