Late Cretaceous dinosaurs and aquatic vertebrates from Mendoza: new palaeoecological evidence of the Atlantic transgression of Patagonia

GONZÁLEZ RIGA, BERNARDO J.; PREVITERA, ELENA; PARRAS, ANA MARÍA

Mendoza

Congreso; Gondwana 12, “Geological and Biological Heritage of Gondwana”; 2005

Gondwana 12 Conference, Organising Committe

Since the early 20th Century, vertebrate remains related to an Atlantic transgression have been recovered from the Los Alamitos and Coli Toro formations, and from the Malargüe Group. While these vertebrates have been well studied systematically (see references cited in Gasparini et al., 2001), only a few taphonomic analysis have been carried out. The study of fossil materials from two areas from Mendoza Province (northern Neuquén Basin), increases the information available on these vertebrates and their habitats. The Neuquén Basin comprises marine and continental deposits of transgressive-regressive episodes. Within this basin, the Malargüe Group includes the Loncoche, Jagüel, Roca and Pircala formations. The sedimentary facies of the Loncoche Formation (Late Campanian – Early Maastrichtian) suggests that 72 million years ago a narrow sea extended from the Atlantic covering northern Patagonia and reached southern of Mendoza Province (Parras et al., 1998). The area around Ranquil-Có (Sierra de Palauco, Mendoza) has yielded diverse vertebrate assemblages. These include freshwater and brackish fish, such as Rajiformes, cf. Atractosteus sp. (Semionotiformes), Percodei (Perciformes) and Metaceratodus sp. (Dipnoi). Reptiles include terrestrial forms, such as snakes (?Matssoidae) and dinosaurs (Theropoda and Titanosauria), freshwater turtles (Chelidae) and marine or littoral taxa (Plesiosauria) (González Riga, 1999). Sedimentologic and paleontological evidences point towards a progressive marine influence from the base of the Loncoche Formation (fluvial, lacustrine, tide-dominated delta and littoral sabkhas) to the overlying Jagüel Formation (marine shelf) (González Riga and Parras 1998). Most vertebrate remains come from tidal channels (parautocthonous-allochtonous concentrations) that indicates transport, depositation and mixing of continental, freshwater and littoral vertebrates. Conversely, the area around Calmu-Co (along the eastern foothills of the Andes) shows less marine influence. In the middle section of the Loncoche Formation, vertebrate remains come from parautochtonous-allochtonous concentrations of fluvial-dominated deltas. These concentrations are composed by fish, i.e., Teleostei, Lepisosteidae, Batoidei and Dipnoi (cf. Metaceratodus sp), turtles Chelidae (cf. Yaminuechelys sp. and Prochelidella sp.), marine reptiles Elasmosauridae, and terrestrial dinosaurs Titanosauria. In the upper section of the formation, parautochtonous concentrations of fragmentary dinosaur bones and wood come from fluvial facies (Previtera, 2005). The differences between the Ranquil-Có and Calmu-Co areas are probably related to the paleogeographic configuration of the marine ingression. Calmu-Co, located along the western margin of the Neuquén Basin, shows a slightly marine influence, whereas Ranquil-Có is placed in the middle of the ancient narrow sea branch that covered southern Mendoza Province. In northern Patagonia and Mendoza Province, the presence of sedimentary environments related to marine transgressions, resulted in optimal habitats for diverse fish and reptiles characterized by different taphonomic histories and paleoecological requirements. Study supported by the IANIGLA-CRICYT and the Project PICT 07-08277of ANPCyT. References Gasparini, Z., de la Fuente, M., Fernández, M., and Bona, P., 2001, Reptiles from Late Cretaceous coastal environments of northern Patagonia: Asociación Paleontológica Argentina, Publicación Especial, no. 7, p. 101-115. González Riga, B. J., 1999, Hallazgo de vertebrados fósiles en la Formación Loncoche, Cretácico Superior de la provincia de Mendoza, Argentina: Ameghiniana, no. 36, p. 401-410. González Riga, B.J., and Parras, A.M., 1998, Paleoambiente y paleontología de la Formación Loncoche (Cretácico Superior) en Ranquil-Có, sur de la provincia de Mendoza, R. Argentina, 7th Congreso Argentino de Paleontología y Bioestratigrafía, Bahía Blanca, Buenos Aires,  Actas, p.  81. Parras, A. M., Casadío S., and Pires, M., 1998, Secuencias depositacionales del Grupo Malargüe y El límite Cretácico-Paleógeno, en el sur de la provincia de Mendoza, Argentina: Asociación Paleontológica Argentina, Publicación Especial, no. 5, p. 61-69. Previtera, E. 2005. Vertebrados fósiles y paleoambientes cretácicos de la Formación Loncoche en Calmu-Co, provincia de Mendoza, Argentina. [Licenciate Thesis]: Mendoza, Universidad del Aconcagua (Argentina), 97 p.