A new ophthalmosaurid (Ichthyosauria) from the Upper Kimmeridgian deposits of the La Casita Formation, near Gomez Farias, Coahuila, northern Mexico

摘要

Recent redescriptions of numerous ophthalmosaurid ichthyosaur taxa have led to a major reinterpretation of the taxonomic and evolutionary hypotheses of the family Ophthalmosauridae. The specimen CPC 238 from the La Casita Formation, Coahuila, Mexico, was first identified as belonging to Ophthalmosaurus icenicus. However, our reexamination of this specimen within the current taxonomic status of Ophthalmosaurus, has allowed for a reclassification of CPC 238 within a new genus and species, Jabalisaurus meztli. The creation of the new genus Jabalisaurus is supported by the presence of four diagnostic characters: 1) posterior lachrymal end separating both nasal and prefrontal bones; 2) an extensive contact between both lachrymal and nasal bones; 3) frontals elongated medially, with a posterior lateral expansion that gives them an L-shape; and 4) a crescent-moon shaped postorbital bone, higher than wide, large, covering more than two-thirds of the postorbital surface of the skull. A new phylogenetic analysis of Ophthalmosauridae conducted in the present study, placed Jabalisaurus meztli in the subfamily Ophthalmosaurinae. The discovery and redescription of J. meztli will contribute to the knowledge of the diversity of ophthalmosaurid ichthyosaurs present in the western domain of the Tethys.