Paleontologist Describes New Genus of Mosasaurs: Gnathomortis stadtmani

Thursday, September 24, 2020

A skeletal mount of the mosasaur Gnathomortis stadtmani at BYU’s Eyring Science Center. Image credit: BYU.

Gnathomortis stadtmani, the only species of the newly-described mosasaur genus, swam in the seas of North America between 79 and 81 million years ago (Cretaceous period).

The partial skull and skeleton of Gnathomortis stadtmani was discovered in the Mancos Shale of Delta County in western Colorado in 1975.

In 1999, the specimen was assigned to the genus Prognathodon and named Prognathodon stadtmani.

In a new study, Dr. Joshua Lively from the Jackson School of Geosciences at the University of Texas at Austin examined the original specimen and the recently-uncovered portions of the mosasaur’s skull roof, jaw, and braincase.

He determined the fossils are not closely related to other species of the genus Prognathodon and needed to be renamed.

“The new name, Gnathomortis, is derived from Greek and Latin words for ‘jaws of death’,” Dr. Lively said.

A cast of the mosasaur Gnathomortis stadtmani’s bones mounted at Brigham Young University’s Eyring Science Center in Provo, Utah. Using phylogenetics and other analysis, Utah State University Eastern paleontologist Joshua Lively described and renamed the new genus, which roamed the oceans of North America toward the end of the Age of Dinosaurs. Credit: BYU

“It was inspired by the incredibly large jaws of this species, which measure 1.2 m (4 feet) in length.”

An interesting feature of the mosasaur’s jaws is a large depression on their outer surface, similar to that seen in modern lizards, such as the collared lizard (Crotaphytus collaris).

The feature is indicative of large jaw muscles that equipped the marine reptile with a formidable biteforce.

“What sets this animal apart from other mosasaurs are features of the quadrate — a bone in the jaw joint that also forms a portion of the ear canal,” Dr. Lively said.

“In Gnathomortis, this bone exhibits a suite of characteristics that are transitional from earlier mosasaurs, like Clidastes, and later mosasaurs, like Prognathodon.”

“We now know Gnathomortis swam in the seas of Colorado between 79 and 81 million years ago, or at least 3.5 million years before any species of Prognathodon.”

The study was published in the Journal of Vertebrate Paleontology.


Joshua R. Lively. Redescription and phylogenetic assessment of ‘Prognathodon’ stadtmani: implications for Globidensini monophyly and character homology in Mosasaurinae. Journal of Vertebrate Paleontology, published online September 23, 2020; doi: 10.1080/02724634.2020.1784183