Calsoyasuchus

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Calsoyasuchus valliceps was an early Jurassic relative of crocodiles that lived in what is now Arizona, USA. Scientists describe it from a single incomplete skull about 38 centimeters long, found in the Kayenta Formation on Navajo Nation land.

The genus name honors Dr. Kyril Calsoya, and the species name “valliceps” means “valley head,” a reference to a deep groove along the midline of the skull bones. The skull shows a long, low shape with a wide-tip snout, several teeth in the snout, and a large number of teeth in the upper jaw. A noticeable groove runs along the midline of the nasal and frontal bones, and the frontal bones are fused. Unlike some later crocodile relatives, Calsoyasuchus had external openings in the skull in front of the eyes (antorbital fenestrae). CT scans revealed air passages and a double-walled palate, features that are similar in some ways to true crocodiles.

Calsoyasuchus is often treated as one of the earliest members of the family Goniopholididae, but its exact position is debated. Some analyses group it with other goniopholids such as Goniopholis and Sunosuchus, while others place it near different crocodyliforms. A 2011 study suggested it is the most basal goniopholidid, a 2019 study linked it more closely to Hsisosuchus, and a 2022 analysis found it among the closest relatives of Thalattosuchia (a different group of crocodile-like reptiles).

This fossil helps push back the appearance of goniopholids into the Early Jurassic, filling gaps in both time and form between early crocodyliforms and later giants of the crocodylian line. The Kayenta Formation at the time hosted a diverse ecosystem with frogs, turtles, other crocodylomorphs, pterosaurs, various dinosaurs, and early mammals.

The holotype skull, labeled TMM 43631-1, was discovered in 1997 during a collaborative expedition and represents a moderately sized animal. The discovery highlights how crocodyliform history stretches much further back than previously thought.