The first rhynchocephalian from the Late Jurassic of South America (Cañadón Calcáreo Formation, Chubut, Argentina)

Abstract

The fossil record of rhynchocephalian lepidosaurs in South America spans from the Late Triassic to the Paleocene, but remains
sparse and elusive. Currently, there are many gaps in our understanding of the diversity and evolutionary history of South American taxa, due to the scarcity of specimens and often fragmentary remains. Here we describe the first Late Jurassic rhynchocephalian from the continent, from the probable Oxfordian Cañadón Calcáreo Formation of Chubut Province, Argentina. The specimen is poorly preserved and represented solely by postcranial elements. The presence of amphicoelous vertebrae with notochordal canal and gastralia allows the identification of this specimen as a rhynchocephalian of unclear affinities. The latest phylogenetic analyses suggest that only neosphenodontians were present in Argentina. Thus, it is likely that the specimen belongs to this derived clade of rhynchocephalians, but the lack of diagnostic features hampers secure referral.