A new Tithonian ophthalmosaurid ichthyosaur from Coahuila in northeastern Mexico

Abstract

Historically, Mexican Jurassic ichthyosaurs have been referred to European representatives of the cosmopolitan family-level clade Ophthalmosauridae. Here, we describe one of the most skeletally complete Mexican ichthyosaur fossils discovered to date. This specimen was recovered from Late Jurassic (Tithonian) deposits of the La Caja Formation exposed near Gómez Farias in the Saltillo municipality of Coahuila, northern Mexico. The unique morphology of the external nasal opening, which is sub-divided by the dorsal process of the maxilla, an anteroposteriorly elongate lacrimal, and the presence of an elongate linear contact between the lacrimal and prefrontal identify these remains as a new genus and species—Parrassaurus yacahuitztli gen. et sp. nov. Other diagnostic character states include an extremely elongate prenarial rostrum, a proportionately large subnarial versus supranarial process on the premaxilla, anterior bordering of the supratemporal fenestra by the frontal, and an articular contact between the humerus and intermedium that separates the ulna and radius. Parrassaurus yacahuitztli represents the second platypterygiine taxon recorded from Mexico to date, and thus demonstrates a greater diversity of North American ophthalmosaurids than has been previously suspected.

Jair Israel Barrientos-Lara* [[email protected]] and Jesús Alvarado-Ortega [[email protected]], Instituto de Geología, Universidad Nacional Autónoma de México, Circuito de la Investigación S/N, Ciudad Universitaria, Delegación Coyoacán, Ciudad de México, 04510 México.

Keywords:

• Parrassaurus
• Late Jurassic
• Ophthalmosauridae
• Platypterygiinae
• Hispanic Corridor

Acknowledgements

We thank Victor Manuel Escalante-Hernández and José Manuel Padilla Gutiérrez (MUDE) for access to specimens. The Chief Editor of Alcheringa, Benjamin Kear, and three anonymous reviewers provided constructive comments and editing of our manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental material

Supplemental research materials for this article can be accessed at https://doi.org/10.1080/03115518.2021.1922755.

Additional information

Funding

Financial support was provided by grants from the Universidad Nacional Autónoma de México [IN207314 and IN110920]. JBL also acknowledges a scholarship from the Consejo Nacional de Ciencia y Tecnología (CONACyT), Mexico.