Two new species of non-Aristonectine Elasmosaurids (Plesiosauria; Sauropterygia) from the Weddellian Province and the origin of the Aristonectinae. .

O'GORMAN, J.P

San Rafael

Congreso; 4° International Paleontological Congress; 2014

The elasmosaurids from the Weddellian province (Patagonia, Western Antarctica and New Zealand) comprises the distinctive large skulled aristonectine (Aristonectes, Kaiwhekea) and the more typical small skulled non-aristonectine elasmosaurids. Here two new non-aristonectine elasmosaurids from the Weddellian Province are commented. The nov. sp. 1 (MLP 93-I-5-1, Museo de La Plata, Argentina) comes from Vega Island, James Ross Archipelago, Antarctica, lower Maastrichtian Cape Lamb Member of the Snow Hill Island Formation. The nov. sp. 2 (MLP 71-II-13-1) comes from Lago Pellegrini, Río Negro, Patagonia (upper Campanian-lower Maastrichtian Allen Formation). The nov. sp. 1 is one of the few Late Cretaceous elasmosaurids from the South Hemisphere whosepostcranial anatomy is well-known. The nov. sp. 1 is distinguished from other elasmosaurids by the following combination of characters: cervical region with 54 vertebrae with elongated centra, dumbbell shaped articular faces and lateral ridge present in the anterior and middle part of the neck but absent in the posteriormost cervical vertebrae; scapula with ventral ramus bearing a strong ridge in the anteromedial corner of its dorsal surface; ilium shaft, with expanded distal end, divided in two parts forming an angle of 140° opening anteriorly; humerus with anterior knee and prominent posterior projection with accessory posterior articular facet. The nov. sp. 2 shares with the nov. sp.1 the humeral morphology (humerus with anterior knee and prominent posterior projection with accessory posterior articular facet) but differs from the nov, sp. 1 in its distinctive small body size (about 3.7 m long), more elongated cervical centra, caudal parapophysis laterally projected and presence of pelvic bar. Preliminary phylogenetic analysis places the nov. sp. 1 and nov. sp. 2 within a clade that includes the Late Cretaceous Weddellian aristonectine elasmosaurids, Aristonectes and Kaiwhekea. This indicates a close relationship between Aristonectinae and non-Aristonectinae Late retaceous Weddellian elasmosaurids and reinforces the hypothesis of the Weddellian origin for the Aristonectinae.