Large early mosasaur species discovered in Mexico

A new species of mosasaur that lived about 90 million years ago has been found in Mexico. The marine reptile was roughly 5.2 metres long, making it one of the earliest large mosasaurs.

Yaguarasaurus regiomontanus is a member of Mosasauridae, a group of extinct marine reptiles that lived underwater while the dinosaurs ruled on land. Mosasaurs were the ocean’s top predators during the Late Cretaceous epoch (100.5–66 million years ago).

The new species lived during the Turonian stage (94–90 million years ago) of the Late Cretaceous.

It’s discovery is detailed in a paper published in the Journal of South American Earth Sciences.

Marine reptiles in Earth’s ancient seas, flying reptiles in the air and the non-avian dinosaurs on land were all wiped out in a mass extinction caused by an asteroid which hit Earth at the end of the Cretaceous.

There are over 40 genera of mosasaur, which were present around the world in the Late Cretaceous.

The largest, Mosasaurus hoffmani, measured 12 metres long—about double that of the largest great white sharks today. But some estimates suggest that it could have reached up to 19 metres. Though a far cry from Steven Spielberg’s mosasaur in the film Jurassic World: Fallen Kingdom (2015), which measured about 70 metres, these marine reptiles were fearsome hunters.

With long, serpentine bodies, it would have been able to reach high speeds and snap up prey in its jaws filled with dozens of teeth.

“Mosasauridae comprise at least four subfamilies: Halisaurinae, Mosasaurinae, Tylosaurinae, and Plioplatecarpinae, although the details of mosasaur relationships remain controversial and a topic of ongoing study,” write the authors, led by Hector Rivera-Sylva, a palaeontologist at Mexico’s Museo del Desierto.

Plioplatecarpine mosasaurs generally had shorter bodies and skulls, and were strong-swimming.

Yaguarasaurus is a plioplatecarpine mosasaurid known from an almost complete, well-preserved skull. The specimen was found in the northeastern Mexico state of Nuevo Leon. It is the first Yaguarasaurus found in Mexico, with other species found in South America.

Fossil skull of a mosasaur
Yaguarasaurus regiomontanus, holotype slab. Scale bar – 10 cm. Credit: Rivera-Sylva et al.

“The new species closely resembles Yaguarasaurus columbianus from the Turonian of Columbia but exhibits derived features suggesting it may be more closely related to later plioplatecarpines,” Rivera-Sylva and his team say.

“It is one of the earliest large mosasaurids and one of the first plioplatecarpines, documenting the initial radiation of mosasaurids in the Turonian following mid-Cretaceous extinctions in the Cenomanian.”

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