First Record of Kawanectes Lafquenianum (Elasmosauridae, Sauropterygia) From La Colonia Formation

JOSÉ P. O'GORMAN

Jornada; 31 Jornadas Argentinas de Paleontología de Vertebrados; 2017

Plesiosaurs are the only vertebrate with marine affinities collected from the upper Campanian-lower Maastrichtian La Colonia Formation, Chubut Province. Both elasmosaurids and polycotylids have been collected from the middle facies association of the La Colonia Formation. Here, a new specimen (MPEF 1155) referred to Kawanectes lafquenianum is described, and new information about its anatomy is added. MPEF 1155 preserves the mandible and cervical, dorsal, sacral, and caudal vertebrae, as well as an almost complete anterior limb, pubis, ischium, both ilia and femora. MPEF 1155 shares with the holotype of Kawanectes lafquenianum (MLP 71-II-13-1) and referred specimens (MUC Pv 92; MCS PV 4) the strongly laterally projected parapophyses in caudal vertebrae and a relatively high humerus length/femur length ratio (~1.2). K. lafquenianum shows a relatively short mandibular symphysis, comprising only 2.5 alveoli. The coronoid process is relatively high and pointed. The distance between the coronoid process and the glenoid cavity is relatively low compared with other elasmosaurids. Additionally MPEF 1155 preserves a complete ilium, indicating that it bears only a slightly expanded distal end, contrary to previous assumptions. Additionally the medial surface bears a slightly concave area. The new specimen is relevant as it bears the first well-preserved mandibular material of a non-aristonectine elasmosaurid collected in Patagonia, providing new data on the plesiosaur fauna of La Colonia Formation and the Weddellian elasmosaurids.