NEW VERTEBRATE REMAINS FROM THE ALLEN FORMATION (CAMPANIAN–MAASTRICHTIAN; UPPER CRETACEOUS) IN RÍO NEGRO, ARGENTINA

ALEXIS M. ARANCIAGA ROLANDO; CERRONI MAURICIO; MOTTA J. MATIAS,; BRISSÓN EGLI F.

La Plata

Congreso; Reunion de comunicaciones cientificas de la APA; 2019

Asociacion Paleontologica Argentina

The “Arriagada fossiliferous site” is located SE from General Roca city, Province of Río Negro, Argentina. In a recent fieldtrip to such locality we collected vertebrate remains, including indeterminate Chelidae turtles, and yet innominate hadrosaurids, indeterminate titanosaurids, aeolosaurines, saltasaurines, and abelisaurid dinosaurs. The best represented abelisaurid specimen is represented by incomplete dentary, braincase, right scapulocoracoid and fragments of vertebrae and ribs. The assignation to Abelisauridae is based on a tear-shaped basisphenoidal recess, posterior surface of basioccipital flattened, and frontals strongly ornamented and dorsoventrally thickened. Fusion of skull elements indicates that the individual was an adult. It reached approximately 4–5 m in whole length, differing from the almost coeval abelisauridsAbelisaurus and Carnotaurus not only by being smaller in size, but for its morphological features. The new abelisaurid shows basal tubera dorsoventrally tall, deep and flat surface between the foramen magnum and the supraoccipital crest, double foramina for middle cerebral vein, and supratemporal fossa deeply excavated anteriorly. Discoveries in “Arriagada site” reveals a new species of a mid-sized abelisaurid, but the remaining components of this diverse dinosaur fauna still require detailed comparison with materials from other sites of the Allen Formation.