Late Cretaceous vertebrates from bajo de Santa Rosa (Allen Formation), Río Negro province, Argentina, with the description of a new sauropod dinosaur (Titanosauridae)

Resumen

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.