GASTROLITHS IN A PLESIOSAUR (SAUROPTERYGIA) FROM THE ALLEN FORMATION (CAMPANIAN-MAASTRICHTIAN), Rio NEGRO PROVINCE, PATAGONIA, ARGENTINA

A group of 389 gastroliths associated to a partially preserved skeleton of a plesiosaur from the Allen Formation (Campanian-Maastrichtian), found in the Rio Negro Province (Patagonia, Argentina), is described. The gastroliths were in situ in the abdominal region of the animal. With respect to their form, spheroidal and discoidal gastroliths, predominated over the laminar. The mean index of sphericity is of 0,686 (d.s +/- 0,108). These two last data suggest that the plesiosaur from Rio Negro, as many others found in other localities of the world (for instance, Kansas and Montana, in the United States), would have ingested the pebbles in the mouths of the rivers. Estimations on this and others plesiosaur specimens suggest that the gastroliths would have had a digestive function, more than hydrostatic.