A Late Cretaceous “tuatara” (Lepidosauria: Sphenodontinae) from South America

Rhynchocephalia achieved a global distribution during the Mesozoic but the history of sphenodontines, the clade containing the extant genus Sphenodon (the New Zealand tuatara), remains poorly understood. Here, we describe a partial maxilla from the Late Cretaceous of Argentina bearing teeth that closely resemble those of modern Sphenodon. This material helps to fill in a notable gap in the fossil history of lepidosaurs because it represents the first evidence of a sphenodontine from South America and increases the number of known Late Cretaceous rhynchocephalian taxa from that region. The morphological disparity encompassed by these records is consistent with suggestions that rhynchocephalians remained diverse in the Late Cretaceous of South America despite a concurrent disappearance from Laurasia. Moreover, the new record supports the hypothesis that sphenodontines were once found widely throughout Gondwana, before its constituent landmasses began to separate about 80 million years ago. The extant Sphenodon probably represents a biogeographic remnant of this distribution, but whether its relatively large size and its ability to remain active at cold temperatures reflects a high latitude ancestry requires further examination.