THE CONTINENTAL CENOMANIAN OF PATAGONIA: A COMPARISON BETWEEN THE FOSSIL VERTEBRATE FAUNAS OF THE RÍO LIMAY SUBGROUP (NEUQUÉN GROUP) AND OF THE BAJO BARREAL FORMATION (CHUBUT GROUP)

CANALE, JUAN IGNACIO; IBIRICU, LUCIO; HALUZA, ALEJANDRO; CASAL, GABRIEL

San Juan

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Cenomanian continental sediments are well represented in Patagonia, and two major stratigraphic units are particularly important regarding their geographic extent and fossiliferous richness. ␣e Río Limay Subgroup, including the Candeleros and Huincul formations, is exposed in the provinces of Neuquén and Río Negro. Secondly, the lower member of the Bajo Barreal Formation outcrops extensively in Chubut Province. These units have yielded a large number of vertebrate fossils and show showing remarkable faunal similarities. ␣e hypothesis of a faunal relationships between those stratigraphic units was tested using an UPGMA cluster analyses (Sokal and Michener, 1958) based on the Bray-Curtis distance coecient (using Jaccard and Simpson similarity coecients). In this analysis were included other stratigraphic units of the Neuquén Group (Río Neuquén and Río Colorado Subgroups) and the Allen Formation (Garrido, 2011). Likewise, the beds preliminarily assigned to the upper member of the Bajo Barreal Formation exposed in the southeastern region of Lago Colhué Huapi were also included (Casal et al., 2006, 2007). Results showed that the latter clearly group with the Allen Formation in particular, and in general with all post-Turonian units analyzed. The analysis revealed from evidence provided by the fossil record– the marked dierence between the faunal associations found in both members of the Bajo Barreal Formation. ␣is agrees with previous proposals about an important diacronism within this Formation (Casal et al., 2007). Cenomanian units analyzed display a strong clustering, characterized by the presence of basal coelurosaurs (Aniksosaurus Martínez and Novas, 2006, and related forms), rebbachisaurids and basal titanosau- riforms (Andesaurus Calvo and Bonaparte, 1991). In addition, they are separated from the rest of the post-Turonian units, which present moderate to strong clustering among them. This pattern suggests that faunal associations of wide geographical distribution in Patagonia suffered a signicant turnover, probably related to an extinction event at the Cenomanian/Turonian boundary (Coria and Salgado, 2005).