Amphicotylus

Ceratosaurus hunting Amphicotylus. Credit: Xiphactinus on DeviantArt.

*Amphicotylus* is an extinct genus of crocodile that lived in Oklahoma and Colorado during the Late Jurassic.

## History

Edward Drinker Cope (1878) described *A. lucasii* from dorsals, lumbars, ribs and osteoderms from the *Camarasaurus supremus* holotype, determining the animal as smaller than the American alligator. It's name is afetr Superintendent Lucas, who discovered the specimens. Cope then collected crania from the same level, but did not refer them to his *Amphicotylus*. Charles C. Mook (1942) examined these crania, refering them to the species based on morphology, lack of associated crocodilian remains and size, rather than just the level. This specimen was designated the neotype. J.W. Stovall examined material similar to *A. gilmorei* that was discovered by the Works Progress Administration in the 1930s. Mook has described these in 1964 as *Goniopholis stovalli*. Eric Randall Allen (2012) argues that this specimen and others like it are differentiated enough from European forms in palate anatomy and fully split chaonae alone to define *Amphicotylus* as a catch-all for Morrison goniopholidids and *Goniopholis* as a catch-all for select European forms. Here, *"Goniopholis" felix* was recombined as A. felix. They also find little differences between *A. lucasii* and *A. gilmorei*, the only character being created by artificial breakage, and so decided to call it a junior synonym of *A. lucasii*, the type species. East *Camarasaurus* Quarry in 1993 has yielded some of the most goniopholidids ever found. This specimen would be exhibited in the Gunma Museum of Natural History since 1996 until Yoshida et al. (2021) would name is *A. milesi*, after Clifford Miles who contributed to museum curation and excavations.

## Description

*Amphicotylus* has a somehwat triangular, platyrostral skull similar to extant crocodilians. The palate anatomy differs from European goniopholidids through the choana severing connection from the palatines, which is shared by *Eutretauranosuchus*. A. milesi has a skull 43 centimeters long, being the largest skull of the genus. *A. milesi* has a hyoid with similar morphology to extant crocodilians. The anterior of the elongate choana was likely coated in soft tissue. The ventral fold of the guilar valve was likely able to raise, which is an adaptation of semi-aquatic life. This would have allowed it to close off the oral cavity from respiration, allowing *Amphicotylus* to open its jaws underwater while breathing through nostrils at the surface of the water. This suggests neosuchian respiratory evolution started in the Jurassic.

## Species

* *A. felix*
* *A. lucasii*
* *A. stovalli*
* *A. milesi*

## Synonyms

* *"G." felix*
* *"G." gilmorei*
* *"G." stovalli*
* *"G." lucasii*

## Classification

*Amphicotylus* is consistently nested within deep goniopholididae, mostly outside of European forms. Puértolas-Pascual et al. (2015) recover *Denazinosuchus* as the sister taxon to *Amphicotylus*, but Yoshida et al. (2021) place this taxon as part of the European clade. De Andrade et al. (2011) find the following:

Yoshida et al. (2021) find:

## References

https://en.wikipedia.org/wiki/Amphicotylus