The oldest lower Upper Cretaceous plesiosaurs (Reptilia, Sauropterygia) from the southern Patagonia, Argentina

JOSÉ PATRICIO O'GORMAN AND AUGUSTO NICOLÁS VARELA

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: La Plata; Año: 2010 vol. 47 p. 447 - 459

0002-7014

THE OLDEST PLESIOSAURS (REPTILIA, SAUROPTERYGIA) FROM THE EARLY LATE CRETACEOUS, SOUTHERN PATAGONIA, ARGENTINA. Plesiosaurs are recorded for the first time from the Mata Amarilla Formation, Santa Cruz, Patagonia Argentina. The stratigraphic succession consists of mudstones and siltstones interbedded with medium to fine-grained sandstone, deposited in a littoral environment during the Cenomanian to Santonian interval, therefore the material is the oldest record of plesiosaurs from the Upper Cretaceous rocks in Argentina. The remains include teeth some vertebrae and one propodium assigned to Elasmosauridae indet and Plesiosauria indet. The assignation of Polyptychodon patagonicus Ameghino, 1893 as well as the stratigraphical position are discussed, leading to the conclusion that the material described by Ameghino is probably from the Mata Amarilla Formation and can only be referred to Plesiosauria indet. The analysis of sedimentological features indicates that the material described here was deposited in an estuarine environment with strong tidal influence. The characters of the inferred environment are consistent with the type of preservation of the materials.