Amphicotylus milesi
Morrison Formation
Upper Jurassic
Moffat County, Colorado

Here is a tooth of the Jurassic crocodile Amphicotylus. It is prepared in its original matrix of Morrison Formation channel sandstone. The tooth is 1.7 cm tall and displays the characteristic striations of the genus. There is no repair or restoration.

Amphicotylus milesi is a member of the Goniopholididae, a group of basal neosuchian crocodyliforms closely related to Paralligatoridae and Eusuchia that lived during the Jurassic and Early Cretaceous. Goniopholidids have the long, flat snout and secondary palate of modern crocodylians, the acquisition of which is regarded as a key feature in the early evolution of crocodylian body plan and their aquatic adaptation. Modern crocodylians are the descendants of a terrestrial crocodyliform ancestor that gave rise to a lineage of successful semi-aquatic predators through the acquisition of a suite of unique characteristics including a long, flat snout, dorsally facing orbits, closable nostrils, a secondary palate and a gular valve.