Dinosaurs in Their Time

Field Guide to the Oviraptorosaur

Eusuchian crocodyliform
(you-SUE-key-en crock-oh-DIE-lih-form)

crocodyliform

Illustration © 2004 Robert F. Walters

This very incomplete skeleton (including a possible skull fragment, several vertebrae, and two dermal scutes) belongs to a small relative of living crocodylians. More specifically, we know it pertains to the group Eusuchia, because its tail vertebrae aredeeply concave in front and convex behind. However, because several eusuchians are known from the Hell Creek Formation, scientists cannot currently determine which of them this fragmentary specimen belongs to. The most abundant eusuchians in this formation are Borealosuchus and Brachychampsa, with Thoracosaurus also present but less common. In addition to Borealosuchus and Brachychampsa, the neighboring Lance Formation has produced fossils of another eusuchian called Prodiplocynodon.

Borealosuchus was a relatively small eusuchian that looked and probably behaved like modern crocodiles, although it is only distantly related to them. Brachychampsa, a relative of today’s alligator, has blunt teeth that seem well-suited to crushing hard objects. For this reason, some scientists think it ate turtles. Thoracosaurus, a long-snouted animal that preferred coastal environments, is a distant relative of the modern gavial, a fish-eating crocodylian that lives in India. Finally, the rare Prodiplocynodon, known from only a single skull, is more closely related to today’s crocodiles than are all other eusuchians from the Hell Creek and Lance formations.

Top and side views of fossils

crocodyliform fossils

crocodyliform fossils

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