A new brachaucheniine pliosaurid (Plesiosauria, Pliosauridae) from the upper Aptian of Villa de Leyva, Boyacá, Colombia

We describe two new pliosaurid specimens from upper Aptian beds near Villa de Leyva, Boyacá, Colombia. Morphological analysis reveals they represent a new brachaucheniine genus and species, <i>Boyacasaurus sumercei</i> gen. et sp. nov. Autapomorphies include: (1) an extremely elongated parasphenoid anterior projection surpassing the posterior interpterygoid vacuity margin, preventing midline pterygoid contact anterior to the posterior interpterygoid vacuity; and (2) palatines exhibiting a slope change near the midline, transitioning from a flat medial surface to a slightly dorsally inclined surface meeting the maxillae. <i>Boyacasaurus</i> is further distinguished by: maxilla forming anterior, lateral, and posterior halves of the internal naris margin; a short maxillary medial process posterior to the internal naris; a rounded basioccipital condyle lacking precondylar constriction and with a weakly developed ventral process; and palatines extending anteriorly beyond the pterygoid. Phylogenetic analysis places <i>Boyacasaurus</i> within Brachaucheniinae, closely related to long-snouted, subtrihedral-toothed pliosaurs <i>Stenorhynchosaurus munozi</i> and <i>Luskhan itilensis</i>. As the youngest recorded subtrihedral-toothed pliosaurid, <i>Boyacasaurus</i> demonstrates that the proposed decrease in Cretaceous pliosaurid dental disparity did not occur before the late Aptian. ZooBank LSID: urn:lsid:zoobank.org:pub:9F237C35-4DF9-467F-A2DB-A3FBD19CDA14