Acuetzpalin carranzai gen et sp. nov. A new ophthalmosauridae (Ichthyosauria) from the Upper Jurassic of Durango, North Mexico

Abstract

The family Ophthalmosauridae gathers the most derived ichthyosaurs from the Middle Jurassic - earliest Late Cretaceous marine deposits of North America, South America, Asia, Europe, and Australia. Although this group has a worldwide distribution, its records from the Caribbean realm, particularly from Mexico, are still comparatively scarce; therefore, the role of these fossils to understand the diversification of the family is negligible. Herein we describe Acuetzpalin carranzai gen. et sp., based on an almost complete specimen from the Kimmeridgian deposits at the Sierra de Palotes, Durango, central Mexico, which belong to the La Casita Formation. This new taxon exhibits a unique combination of features supporting its taxonomical singularity; these include the presence of the parietal foramen entirely surrounded by the parietals, a robust and short supratemporal process on the parietal, a long middle parietal symphysis, the internal carotid foramen exposed on the posterior surface of the basisphenoid, stapedial shaft moderately slender, the opisthotic and stapedial facets of the basioccipital laterally exposed, the intermedium separates the radius from the ulna and has no contact with the humerus, and the nasal lacks the lateral “wing” over the dorsal border of the naris. This fossil, the second ophthalmosaurid species found in Mexico, complements the ichthyosaurs diversity in the western domain of the Tethys Sea, at the southern end of North America. A phylogenetic analysis reveals that Acuetzpalin carranzai is member of the subfamily Platypterygiinae and is located among the most-derived platypterygiines. A new fossil ichthyosaur is described from the Kimmeridgian outcrops of the Sierra de Palotes, near Cuencamé, Durango, Mexico. Acuetzpalin carranzai gen. et sp. is the second ophthalmosaurid species found in Mexico. This discovery expands the knowledge on the Late Jurassic ichthyosaur diversity from the Caribbean region.