Stenorhynchosaurus munozi, gen. et sp. nov. a new pliosaurid from the Upper Barremian (Lower Cretaceous) of Villa de Leiva, Colombia, South America

Abstract

From one of the most complete Lower Cretaceous rock sequences in the world (in Villa de Leiva region, central Colombia), we describe a new genus and species of pliosaurid plesiosaur Stenorhynchosaurus munozi. Stenorhynchosaurus displays a series of features which differentiate it from all the other Cretaceous pliosaurid genera: the anterior of the vomer, in ventral view, posterior of the palatal premaxilla-maxilla suture, contacting the posterior palatal process of the premaxilla level with the third maxillary alveolus; rostrum narrow and elongated with straight sides in dorsal view; lacrimal forming the anterior border and greater part of the ventral border of the orbit and broadly borders the maxilla anteriorly; anterior interpterygoid vacuity present; internal nares located between vomer and maxilla at the level of 13th-15th maxillary alveoli; anterior of rostrum and mandible without lateral expansion or marked increase in size of the functional alveoli; penultimate premaxillary alveolus slightly larger than adjacent premaxillary alveoli; homodont maxillary functional alveoli, with fourth tooth positions very slightly enlarged with respect to the neighboring alveoli; homodont dentary dentition; and epipodials extremely short. Based on morphological analysis of phylogenetic characters, Stenorhynchosaurus most likely nests within the increasingly inclusive Pliosauridae and Pliosauroidea, however, as currently defined, firm inference for referral of Stenorhynchosaurus to Thalassophonea is much more problematic, but ultimately seems likely based on characters shared with Pliosaurus and Brachaucheninae. However, this uncertainty indicates Thalassophonea requires rigorous redefinition. As to whether Stenorhynchosaurus is a member of the currently exclusively Jurassic genus Pliosaurus, or the Cretaceous sub-family Brachaucheninae, remains equivocal.