CERDA Ignacio Alejandro
congresos y reuniones científicas
Elasmosaurs (Sauropterygia, Plesiosauria) from La Colonia Formation (Campanian-Maastrichtian), Chubut, Argentina.
JOSE PATRICIO OGORMAN; LEONARDO SALGADO; ZULMA BRANDONI DE GASPARINI; JULIO VARELA; ANA PARRAS; IGNACIO A. CERDA; JULIANA STERLI; DIEGO POL; PABLO PUERTA; BELEN ROSSO
General Roca, Río Negro.
Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina?, Noviembre de 2012,; 2012
La Colonia Formation (Campanian-Maastrichtian) crops out in the north east of Chubut Province, Argentina. The second facies association of the La Colonia Formation, where several elasmosaur specimens were recently collected from sections located to the north of the Cerro Bayo, was deposited in a marine marginal environment. The new material shares with some Elasmosauridae indet. from the Allen Formation (Río Negro) a distinctive small size and caudal vertebrae with parapophyses strongly projected laterally which indicate a possible relationship between the plesiosaur faunas from the north and south of the Somún Curá Plateau. The distinctive small body size of these elasmosaurs could be related with marginal marine environments. The specimen (MPEF MPEF-PV 10602 was collected in association with 197 gastroliths. Most of the gastroliths are discoidal (41.9%) or spheroidal (34.8%), with a mean Maximum Projection Sphericity Index value of 0.69 and a mean OP Index value of -0.74. These values of these are similar to those recorded for clasts from fluvial environments. This result is congruent with the values calculated for other gastroliths sets associated with Upper Cretaceous elasmosaurs that indicates a fluvial or estuarine origin. Therefore this indicates that at least some Upper Cretaceous elasmosaurs entered into estuarine (or fluvial) environments and helps explaining the interesting vertebrate assemblage of the Allen and La Colonia formations, where a rich continental fauna is recorded, but elasmosaurids and polycotylids are up to now the only well represented vertebrates with marine affinities.