Dinosaurs and environments from the Cretaceous of the Province of Mendoza, Argentina

GONZÁLEZ RIGA, BERNARDO J.

IANIGLA, 30 años de investigación básica y aplicada en ciencias ambientales

Instituto Argentino de Nivología, glaciología y Ciencias Ambientales

Lugar: Mendoza; Año: 2002; p. 197 - 202

At the south of the province of Mendoza, close to the northern extreme of the Argentine Patagonia there are large outcrops of sedimentary sequences from the Cretaceous Period. These same sequences in the neighboring province of Neuquén have contributed important and numerous dinosaur fossils of worldwide importance. But until a few years ago dinosaurs proceeding from Mendoza were completely unknown. Nevertheless the development of intense paleontologic explorations and the communication of findings carried out by oil workers and inhabitants of the region in the last decade, have provided knowledge about the dinosaur dwelling in the south of Mendoza and their relation with fauna from northern Patagonia and from other parts of the world. Up to now the only sedimentary rocks yielding dinosaur fossils are those from the Upper Cretaceous. The findings have been made in the Neuquén Group and in the Loncoche Formation, lithostratigraphic units of the Cuenca Neuquina. During the Jurassic and Cretaceous Periods this basin formed a large depression extending over to the province of Neuquén and parts of the provinces of La Pampa, Río Negro and Mendoza. Marine, continental and littoral sediments were cyclically deposited in this region owing to transgressive and regressive episodes, that is to say advances and retrocession of the sea over the continent. The Neuquén Group is the unit yielding the largest amount of dinosaur fossils. It comprises sandstones, conglomerates and pelites from fluvial, alluvial and playa lake environments developed between the Cenomanian and the early Campanian. Paleontological explorations carried out in the region of Cañadón Amarillo and other sites at the Department of Malargüe, have resulted in the extraction of numerous fossils of Titanosauria herbivore dinosaurs and of other vertebrates. Numerous and significant titanosaur fossils were extracted between 1999 – 2001, together with remains of Theropoda carnivore and Chelidae turtles. Many titanosaur bones of different sizes and ontogenetic development degree were found in several fossiliferous sites. The juvenile individuals were not longer than 7 m, while the medium size adults reached 18 m and weighed 19 tons. Giant specimens, which would have duplicated such weight, were also found. Systematical and phylogenetical studies allowed the recognition of two new species of titanosaurs, the first ones described for the province of Mendoza. One of them shows evolutive newness (autapomorphies) in their caudal and dorsal vertebrae, and osteoderms, which are large bony plates protecting the back and tail. Their study contributes to the knowledge of the diverse adaptive types that titanosaurs developed during the Upper Cretaceous.