title: The youngest South American rhynchocephalian, a survivor of the K/Pg extinction.
abstract: Rhynchocephalian lepidosaurs, though once widespread worldwide, are represented today only by the tuatara (Sphenodon) of New Zealand. After their apparent early Cretaceous extinction in Laurasia, they survived in southern continents. In South America, they are represented by different lineages of Late Cretaceous eupropalinal forms until their disappearance by the Cretaceous/Palaeogene (K/Pg) boundary. We describe here the only unambiguous Palaeogene rhynchocephalian from South America; this new taxon is a younger species of the otherwise Late Cretaceous genus Kawasphenodon. Phylogenetic analysis confirms the allocation of the genus to the clade Opisthodontia. The new form from the Palaeogene of Central Patagonia is much smaller than Kawasphenodon expectatus from the Late Cretaceous of Northern Patagonia. The new species shows that at least one group of rhynchocephalians not related to the extant Sphenodon survived in South America beyond the K/Pg extinction event. Furthermore, it adds to other trans-K/Pg ectotherm tetrapod taxa, suggesting that the end-Cretaceous extinction affected Patagonia more benignly than the Laurasian landmasses.
authors.affiliation: CONICET-Fundación de Historia Natural 'Félix de Azara'-CEBBAD-Universidad Maimónides, Hidalgo 775, Buenos Aires 1405, Argentina sebapesteguia@gmail.com.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Apesteguía
authors.affiliation: CONICET-Departamento de Ciencias Geológicas, Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires, Pabellón 2, Ciudad Universitaria, Buenos Aires 1428, Argentina.
authors.forename: Raúl O
authors.initials: RO
authors.lastname: Gómez
authors.affiliation: Department of Anatomical Sciences and Neurobiology, University of Louisville, 500 South Preston Street, Louisville, KY 40292, USA.
authors.forename: Guillermo W
authors.initials: GW
authors.lastname: Rougier
mesh_terms: D000818:Animals; D001118:Argentina; D005580:Fossils; D007568:Jaw / Q000033:anatomy & histology; D010802:Phylogeny; D012104:Reptiles / Q000033:anatomy & histology / Q000145:classification*; D014070:Tooth / Q000033:anatomy & histology
keywords: cretaceous/palaeogene boundary; opisthodontia; palaeocene; patagonia; rhynchocephalia