Abstract
A large and diverse collection of vertebrate remains from the Campanian-Maastrichtian Allen Formation (Malargue Group) at the Bajo deSanta Rosalocality (Rio 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.
Highlights
During ttie summer of 1990, 1.991, and 1994 fieldworks direct.cd by Dr Jos6 I? Bonaparlo arid carried out by staff from the Museo Argentino de Ciencias Naturales *Bernardino Rivadaviam were conducted a t the Bajo de Santa Rosa locality
Rio NegroProvince, Argentina (Fig. 1).Arich and diverse collection of vertebrate remains was recovered from outcrops of the Allen Formation (Table 1).These fossil reinairis identified are: chondrichthyans; diploinystid siluriforrns, Iepisosteid, proi~abiypercichthyid, and dipnoid osteichthyans; pipid and leptodactylid anurans; chelid turtles; sphenodonts; elasmosaurid plesiosaurs; madtsoiid snakes; and hadrosaurid, titanosaurid, and probably carcharodontosaurid dinosaurs (Table 2)
Ttie aim of'this contribution is to describe the vertebrate fossils collected from the Allen Formation at the Bajo de Santa Rosa locality
Summary
The Bajo de Santa Rosa locality is 1ocal.ed approximately 150 km south west from ttie city of lamarque, approximately in the so~itherncenter of the Rio Negro Province (Fig, 1 ). In this area, the exposed Mesozoic sedimentary rocks correspond to three Late Cretaceousformations: Bajo de la Carpa, Allen, and Jagiiel (Hugo & Lcanza, 2001).The Bajo de la Carpa Forrnation belongs to the Rio Colorado Subgroup from the Neuqu4n Group (Hugo & Leanza, 2001) and its age is presumed to be Coniacian-Santoniari (Legarreta & Gulisai~o,1989; Bonaparte, 1991).
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