Paleontologists have identified a new species of extinct crocodyliform from the fossilized remains of a juvenile individual found in southwest Montana, the United States.
An artist’s impression of Thikarisuchus xenodentes. Image credit: Dane Johnson / Museum of the Rockies.
The newly-described species lived at the edge of the ancient Western Interior Seaway about 95 million years ago (Late Cretaceous epoch).
Named Thikarisuchus xenodentes, the ancient creature was a type of neosuchian.
“Measuring no more than 60 cm (2 feet) long from nose to tip of tail, this Thikarisuchus xenodentes individual was about the size of a big lizard,” said Montana State University’s Professor David Varricchio.
“Had it lived to be full grown, it would have measured no longer than 90 cm (3 feet), far smaller than most members of the Neosuchia clade to which it and its distant relatives belong.”
“The clade includes modern crocodilians and their closest extinct relatives, almost all of them semiaquatic or marine carnivores with simple, conical teeth.”
“Thikarisuchus xenodentes, by contrast, lived on the land, probably feasting on both plants and insects or small animals with its assortment of differently shaped and specialized teeth.”
“Its unique anatomy reveals that it was part of a new, previously unrecognized family of crocodyliforms endemic to the Cretaceous of North America.”
The fossilized bones of Thikarisuchus xenodentes — including its limbs, vertebrae, jaw and 50-mm-long skull — were found in the summer of 2021 in the Blackleaf Formation on U.S. Forest Service land near Dillon, Montana.
“We have found dinosaurs in the Blackleaf Formation before, but this was the second known vertebrate animal we’d ever found in this formation,” said Harrison Allen, a doctoral student at Stony Brook University.
The paleontologists discovered that the bones of Thikarisuchus xenodentes were densely concentrated and organized in a manner consistent with fossils of organisms found in burrows in the Blackleaf Formation and the nearby Wayan Formation in Idaho.
“This suggests that Thikarisuchus xenodentes was likewise preserved within a burrow, further supporting the notion that fossils recovered from these formations are biased toward those that were preserved in burrows,” they said.
The specimens also presented clues about Thikarisuchus xenodentes’ newly-named family group Wannchampsidae and a similar group found in Eurasia known as Atopasauridae.
Both groups were tiny and terrestrially adapted, and they shared certain cranial and dental features found in another more distantly related group from the Cretaceous of Africa and South America.
“It suggests that during the same time period, we’re seeing convergent evolution between two distantly related groups due to similar environmental conditions, prey availability and who-knows-what that prompted crocs on opposite sides of the planet to develop similar features,” Allen said.
“The majority of diversity of crocodyliforms is in the past. There were fully marine crocs, fully terrestrial crocs, herbivorous crocs, omnivores and some that cracked shells.”
“That amazed me and made me want to get into this more specific realm of paleontology.”
A paper on the findings will be published in the Journal of Vertebrate Paleontology.
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Harrison Allen et al. 2025. A new, diminutive, heterodont neosuchian from the Vaughn member of the Blackleaf Formation (Cenomanian), Southwest Montana, and implications for the paleoecology of heterodont neosuchians. Journal of Vertebrate Paleontology, in press; doi: 10.1080/02724634.025.2542185
