A new Cretaceous thyreophoran from Patagonia supports a South American lineage of armoured dinosaurs

The early evolution of thyreophoran dinosaurs is thought to have occurred primarily in northern continents since most evidence comes from the Lower and Middle Jurassic of Europe and North America. The diversification into stegosaurs and ankylosaurs is obscured by a patchy fossil record comprising only a handful of fragmentary fossils, most with uncertain phylogenetic affinities. Here we report the discovery of a new armoured dinosaur from the early Late Cretaceous of Argentina, recovered phylogenetically using various datasets either as a basal thyreophoran or a stem ankylosaur, closely related to Scelidosaurus. It bears unusual anatomical features showing that several traits traditionally associated with the heavy Cretaceous thyreophorans did not occur universally. Jakapil kaniukura gen. et sp. nov. is the first definitive thyreophoran species from the Argentinian Patagonia. Unlike most thyreophorans, it seems to show a bipedal stance, as in Scutellosaurus. Jakapil also shows that early thyreophorans had a much broader geographic distribution than previously thought. It is a member of an ancient basal thyreophoran lineage that survived until the Late Cretaceous in South America.The authors thank to Mariluan family for kindly allowing us the access to the fossiliferous locality of Cerro Policia and to the Secretaria de Cultura of the Rio Negro Province for allowing the respective permits; to the Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Agencia Nacional de Promocion de la Investigacion, el Desarrollo Tecnologico y la Innovacion (projects PICT 2014-0564 and PICT 2018-04598), the Fundacion Azara-Universidad Maimonides, the Spanish Ministerio de Ciencia, Innovacion e Universidades and the European Regional Development Fund (projects CGL2017-85038-P and PID2021-122612OB-I00), and the Gobierno Vasco/EJ (research group IT1418-19) for the funding. F. J. R. thanks to I. Diaz-Martinez, A. Martinelli, L. Leahey, R. Molnar, A. Vargas Milne, S. Soto Acuna, and M. Baron for digital material; to L. Pazo and J. Kaluza for the material preparation; to the members of the Area de Paleontologia of the Fundacion Azara, especially F. Garberoglio, L. Fernandez Dumont and J. P. Garderes, for all the helping; to R. Ponti for the thin sectioning, and I. Cerda for his advice on histological aspects; to S. Bogan, S. M. alvarez and J. Meluso for facilitate the access to the Fundacion Azara collections. S. A. acknowledges J. Kaluza for identifying key materials. Thanks to R. Glasgow for reviewing the English text of the manuscript. Special thanks to the reviewers Susannah Maidment, Victoria Arbour, and an anonymous reviewer, whose comments strongly improved the manuscript