New species of extinct crocodile rewrites life on Triassic coast

The surprising discovery of a new species of extinct crocodile from the Triassic Favret Formation in Nevada, USA, rewrites the story of life along the coasts during the first act of the Age of Dinosaurs.

Described in a study published in Biology lettersThe new species Benggwigwishingasuchus eremicarminis reveals that while giant ichthyosaurs ruled the oceans, ancient relatives of crocodiles known as pseudosuchian archosaurs ruled the globe’s coasts in the Middle Triassic period between 247.2 and 237 million years ago.

“This exciting new species demonstrates that pseudosuchians occupied coastal habitats globally during the Middle Triassic,” said Dr. Nate Smith, lead author of the paper, and Gretchen Augustyn, director and curator of the Dinosaur Institute at the Natural History Museum of Los Angeles County.

Capturing fossil life from the Triassic Eastern Panthalassan Ocean, the locality that includes the Favret Formation is known for its fossils of marine creatures like ammonites as well as marine reptiles like the giant ichthyosaur C. youngorum. The discovery of the newly described B. eremicarminis came as a bit of a shock.

“Our first reaction was: What the hell is this?” said Nicole Klein, co-author of the study and professor at the University of Bonn. “We expected to find marine reptiles. We didn’t understand how a land animal could be found so far out in the sea, among ichthyosaurs and ammonites. It was only when I saw the almost completely prepared specimen in person that I was convinced that it was indeed a land animal.”

Pseudosuchian archosaurs have been discovered in fossil deposits on the coasts of the ancient Tethys Ocean, but this is the first coastal representative from the Panthalassan Ocean and the Western Hemisphere, revealing that these crocodile relatives were present in coastal environments worldwide during the Middle Triassic. Interestingly, these coastal species are not all from the same evolutionary group, suggesting that pseudosuchians (and archosauriforms more broadly) adapted independently to life along coasts.

“Essentially, it looks like several very different groups of archosauriforms decided to dip their toes in the water during the Middle Triassic. What’s interesting is that it doesn’t look like many of these ‘independent experiments’ led to broader radiations of semi-aquatic groups,” Smith said.

During the Triassic, archosaurs, the “dominant reptiles”, appeared and split into two groups with two surviving representatives: birds, descendants of dinosaurs, and crocodilians (alligators, crocodiles and gharials), descendants of pseudosuchian archosaurs such as B. eremicarminis.

While modern crocodilians are similar enough to be confused by most people, their ancestors were very different in size and lifestyle. The evolutionary relationships between B. eremicarminis and its relatives suggest that pseudosuchians reached great diversity very quickly after the end-Permian mass extinction, the extent of which has yet to be discovered in the fossil record.

“A growing number of recent discoveries of Middle Triassic pseudosuchians suggest that an underappreciated amount of morphological and ecological diversity and experimentation was occurring early in the group’s history. While much of the public fascination with the Triassic focuses on the origin of dinosaurs, it was actually pseudosuchians that were doing interesting things in the early Mesozoic,” Smith said.

This new species highlights the multiplicity of these ancient reptiles during the Triassic, from giants like Mambawakale ruhuhu to smaller animals like the recently described B. eremicarminis, which probably reached about 1.5 to 1.8 m in length. The exact length of B. eremicarminis and how it survived along the coasts remain obscure in the past.

Only a few pieces of the individual’s skull have been found, and no clues about how it fed and hunted have been found. What is clearer is that B. eremicarminis probably stayed fairly close to shore. Its well-preserved limbs are well-developed and show no signs of aquatic life, such as fins or altered bone density.

The research team wanted a name that would honor the early human inhabitants of the Augusta Mountains where the specimen was found, and so consulted with a member of the Fallon Paiute Shoshone tribe to decide on an appropriate name.

“Benggwi-Gwishinga,” a word meaning “to catch fish” in the Shoshone language, was combined with the Greek word for Sobek, the Egyptian crocodile-headed god, to create the new genus, Benggwigwishingasuchus. The specific epithet eremicarminis translates to “song of the desert,” in honor of two NHMLAC supporters who have a passion for paleontology and Southwestern opera. Thus, the full name is supposed to translate roughly to “Desert Song of the Fishing Crocodile.”