New small reptile remains from the Late Cretaceous of Patagonia increase morphological diversity of sphenodontids (Lepidosauria)

Abstract

Sphenodontids are a group of reptiles that were diverse and global for much of the Mesozoic but today they are only represented by the New Zealand tuatara. Here we describe new sphenodontid remains coming from the Cretaceous (Maastrichtian) Los Alamitos Formation, at Río Negro province, Argentina. Previous reports in the stratigraphical unit included an indeterminate sphenodontid and the enigmatic Kawasphenodon. The new material here reported includes an isolated and incomplete dentary and a palatine bone. The dentary belongs to a small taxon having quadrangular teeth and an interlocked mandibular symphysis. The palatine shows compressed teeth and a fang-like canine. These specimens probably belong to two new taxa. These, together with Kawasphenodon, suggest that Maastrichtian sphenodontians from northern Patagonia were at least as diverse as those reported from Cenomanian beds. This contrasts with the poorer record of lizards in the same beds. However, the record of Maastrichtian sphenodonts in southern Patagonia is restricted to a single finding of a Sphenodontine sphenodontid. In Australasia the sphenodont record is also restricted to Cenozoic sphenodontines, very similar to extant Sphenodon species. The currently available fossil record suggests that northern Patagonian rhynchocephalians were more morphologically diverse than those of southern Patagonia and Australasia during the Cretaceous, probably reflecting another faunistic particularity of the 'Weddelian Bioprovince'.