Yaguarasaurus columbianus (Reptilia,Mosasauridae), a primitive mosasaur from the Turonian (upper cretaceous) of Colombia

New remains of Yaguarasaurus columbianus found in the Turonian beds of the upper valley of the Magdalena River, in Colombia, are described. Three aspects of the cranial morphology of Y. columbianus are of particular interest. First, its morphology is one of the most primitive among mosasaurs; second, it exhibits most similarities to the cranial morphology of the aigialosaurs; and finally, it exhibits some traits that are unknown in other mosasaurs, including certain cranial features that resemble those of the terrestrial varanoids.