Oneirosaurus caballeroi gen. et sp. nov., un nuevo mosasaurio de Colombia

A new mosasaur specimen found in the Coniacian beds of Lebrija, Santander, Central Colombia, is here described. The new specimen represents a new genus and species of plioplatecarpine mosasaurid that we name Oneirosaurus caballeroi gen. et sp. nov. Oneirosaurus is a plioplatecarpine characterized by one character unknown in any other plioplatecarpine: the presence of two external foramina for the exit of nerves X, XI, and XII. It is also distinguished by a combination of characters that includes among others: prefrontal and postorbitofrontal separated at the roof of the orbit; broad frontal, with short triangular surface anterior to the orbits; triangular and broad anterodorsal surface of the parietal contacting the postorbital for a short distance; infrastapedial process of the quadrate robust without being fused to the suprastapedial process; small otosphenoidal crest of prootic not covering the exit of nerve VII; basioccipital canal opening into the floor of the braincase through two large foramina separated by a medial septum; lingual alveolar parapet of dentary lower than labial; marginal teeth crown with subcircular cross-section at base and with two carinae arranged at 180º; and presence of a notch in anterior border of the atlas neural arch. The morphological comparisons and the cladistic analysis show the new taxon as an intermedium plioplatecarpine with phylogenetic proximity to the Colombian species Yaguarasaurus columbianus from the lower Turonian and to the species Ectenosaurus clidastoides from the Santonian-Campanian of the USA. Our phylogenetic results shows tethysaurines and halisaurines as plesiopelvic and plesiopedal groups separated from the hydropelvic and hydropedal derived groups Tylosaurinae, Plioplatecarpinae, and Mosasaurinae.