First record of Kawanectes lafquenianum (Plesiosauria, Elasmosauridae) from the La Colonia Formation of Argentina, with comments on the mandibular morphology of elasmosaurids

Abstract

The elasmosaurid plesiosaur Kawanectes lafquenianum is recorded from the upper Campanian–Maastrichtian levels of the La Colonia Formation in Argentina for the first time, thus extending the stratigraphical range of this taxon, which was previously recorded only from the geographically proximal Allen Formation. The new fossils are referrable to K. lafquenianum on the basis of the large posterodistal projection on the humerus supporting an articular facet for a proximal supernumerary ossification, the presence of a depression anterior to the main muscle scar on ventral surface of the humeral shaft, and a high humerus/femur length ratio ( 1.2). Novel diagnostic character states for K. lafquenianum include the presence of a high triangular and distally pointed coronoid process on the mandible, a mandibular symphysis that incorporates 2.5 alveolar spaces on each ramus, and a retroarticular process without dorsal or medial inflexion. Relatively low b/a ratio (measure of coronoid–glenoid cavity length/preglenoid length) could suggest a mechanical advantage toward fast jaw closure and weak bite forces. Comparisons with other elamosaurids this imply that Southern Hemisphere weddellonectian taxa, such as K. lafquenianum, Aristonectes parvidens and Kaiwhekea katiki, were possibly adapted for rapid snapping bites.