Calsoyasuchus

Calsoyasuchus (meaning "[Dr. Kyril] Calsoyas' crocodile") is a genus of goniopholidid mesoeucrocodylian that lived in the Early Jurassic. Its fossilized remains were found in the Sinemurian-Pliensbachian-age Kayenta Formation on Navajo Nation land in Coconino County, Arizona, United States. Formally described as C. valliceps, it is known from a single incomplete skull which is unusually derived for such an early crocodile relative. This genus was described in 2002 by Ronald Tykoski and colleagues; the species name means "valley head" and refers to a deep groove along the midline of the nasal bones and frontal bones.

The holotype skull (TMM 43631-1) that would be named Calsoyasuchus was discovered in 1997 by members of an expedition composed of crews from Texas Memorial Museum of the University of Texas at Austin, the Museum of Comparative Zoology at Harvard University, and the Seba Dalkai Navajo Nation School. It was found in the middle third of the silty facies of the Kayenta Formation, near the Adeii Eechii Cliffs. The skull is missing the lower jaws, part of the palate, most of the suspensorium (the bones that make up the region where the upper and lower jaws articulate), and the occiput and braincase. Sutures between the skull bones are mostly fused. As preserved, it is about 38.0 centimeters (15.0 in) long, making its owner a moderately sized animal.