A short-necked plesiosaur (Plesiosauroidea, Polycotylidae) from the upper cretaceous of North Patagonia

摘要

A SHORT-NECKED PLESIOSAUR (PLESIOSAUROIDEA, POLYCOTYLIDAE) FROM THE UPPER CRETACEOUS OF NORTH PATAGONIA. Several plesiosaur vertebrae found in the Allen Formation (late Campanian-early Maastrichtian; Upper Cretaceous), at Loma Puntuda locality, Salitral de Santa Rosa, Rio Negro Province, Argentina, are described. Some anatomical features, such as the amphicoelous vertebral centres higher rather than longer, a ring surrounding the posterior articular surface of the cervical vertebrae, a ventral keel in the cervical vertebrae, the cervical neural spines expanded distally and probably inclined posteriorly, and the lateral surfaces of the dorsal bodies strongly compressed, justify their assignation to the Polycotylidae, a short-necked plesiosauroid group relatively frequent in the Upper Cretaceous of North America. This is the first record of postcranial remains of a polycotylid in South America, where these plesiosaurs were known only by cranial and mandibular remains (assigned to Sulcusuchus erraini Gasparini and Spalletti) found in equivalent stratigraphic levels (Campanian-Maastrichtian), in the Chubut and Rio Negro Provinces.