Cranial anatomy of Kawanectes lafquenianus (Plesiosauria; Elasmosauridae) from la colonia formation with comments on the paleobiogeography of the weddellonectians

Abstract

A new, well-preserved specimen of the small-bodied elasmosaurid Kawanectes lafquenianus (corrected name) from the La Colonia Formation (Upper Maastrichtian, Patagonia, Argentina) provides unprecedented insights into its cranial anatomy and phylogenetic relationships. The specimen comprises a nearly complete skull and partial postcranial skeleton, enabling a detailed morphological description and an updated diagnosis of the taxon. Notable new features include a high sagittal crest, a convex ventral orbital margin, the absence of the posterior interpterygoid symphysis and a plate-like quadrate ramus of the pterygoid. Additionally, a distinctive gracile ectopterygoid forms the caudal and medial margin of a well-developed suborbital fenestra, a feature never seen in other elasmosaurids. Phylogenetic analysis supports Kawanectes lafquenianus as a member of Weddellonectia, closely related to Vegasaurus molyi. Paleobiogeographic reconstruction using BioGeoBEARS indicates that the Western Interior Seaway is the most likely ancestral area for Elasmosauridae, while the origin of Weddellonectia and Aristonectinae is inferred to be southern South America. These findings corroborate previous research on the phylogenetic placement of Kawanectes and enhance our understanding of elasmosaurid evolution, and highlighting the significance of South American records in reconstructing Late Cretaceous marine reptile biogeography.