Late Cretaceous vertebrates from bajo de Santa Rosa (Allen Formation), Río Negro province, Argentina, with the description of a new sauropod dinosaur (Titanosauridae)
A large and diverse collection of vertebrate remains from the Campanian-Maastrichtian Allen Formation (Malargüe Group) at the Bajo deSanta Rosalocality (Río Negro Province,Argentina) is described here. The vertebrates are represented by: chondrichthyans; diplomystid siluriform, lepisosteid, cf. percichthyid and dipnoid osteichthyans; pipid and leptodactylid anurans; chelid turthes; sphenodonts; elasmosaurid plesiosaurs; madtsoiid snakes; faveoolitid and megaloolithid eggshells; and hadrosaurid, cf. carcharodontosaurid and titanosaurid dinosaurs. A new small saltasaurine titanosaurid, Bonatitan reigi gen. et sp. nov., is described. It is diagnosed by the following association of characters: 1) longitudinal groove located on the suture between parietals that continues posteriorly over the supraoccipital to the foramen magnum; 2) basisphenoid tubera long and narrow (more than twice as long as wide); 3) dorsal to middle caudal vertebrae with deep oval to circular pits present on both sides of the prespinal lamina; 4) anterior caudal vertebra with spino-postzygapophysial and spino-prezygapophysial laminae; 5) neural arch of anterior caudals with deep interzygapophysial fossae with numerous pits; 6) anterior caudal vertebra with an accessory sub-horizontal lamina extending from the antero-ventral portion of the postzygapophysis to the mid-portion of the spino-prezygapophysial lamina; and finally, 7) anterior caudal vertebra with a prominent axial crest on the ventral surface of the cemtrum. The first record of sphenodonts and cf. carcharodontosaurid theropods is recognized for the upper Late Cretaceous of Patagonia, as well as the earliest record of percichthyids (Perciformes). The vertebrate record is mainly composed of terrestrial and freshwater taxa, but a few marine elements are found (elasmosaurids) indicating a marine influence during the deposition of the Allen Formation in the area of Bajo deSanta Rosa. The vertebrate remains support a Campanian-Maastrichtian age for the Allen Formation. Comparisons with other South American Campanian-Maastrichtian localities suggest a similar fossil vertebrate composition, with relatively few differences between the Patagonian and extra Patagonian South American records. Key words: Late Cretaceous, osteichthyans, chondrichthyans, anurans, turtles, sphenodonts, plesiosaurs, ophidians, dinosaurs,Patagonia.
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