Oneirosaurus
Oneirosaurus is an extinct genus of plioplatecarpine mosasaurid known from the Late Cretaceous Galembo Formation of Colombia. The genus contains a single species, Oneirosaurus caballeroi, known from a well-preserved skull and mandible.
Discovery and naming
In 1997, Jaime Caballero reported the discovery of a mosasaur skull to the Servicio Geológico Colombiano. The specimen comprises a nearly complete skull articulated with the mandible and the atlas. It was collected in outcrops of the Galembo Formation near the Barrancabermeja-Bucaramanga highway in Lebrija municipality, Colombia. After Caballero's death, his family donated the specimen to the SGC for study. The SGC subsequently revisited the quarry from which the skull was found and discovered pieces of vertebrae and ribs. It is uncertain if these elements belong to the same individual as the skull. The specimen was initially reported by María Eurídice Páramo-Fonseca in 2012 under the specimen number IPN-2, where it was briefly described as a new specimen generally comparable to—but distinguishable from—Yaguarasaurus columbianus. It is now accessioned under the specimen number IGMp879524 at the José Royo y Gómez National Geological Museum.In 2025, Páramo-Fonseca and colleagues described Oneirosaurus caballeroi as a new genus and species of mosasaurid, establishing IGMp879524 as the holotype specimen. The generic name, Oneirosaurus, combines the Greek words όνειρο, meaning, and σαῦρος, meaning "lizard", in reference to the exquisite preservation of the delicate cranial structures in the holotype. The specific name, caballeroi, honors Jaime Caballero, the discoverer of the specimen.