| Calsoyasuchus | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Archosauria |
| Clade: | Pseudosuchia |
| Clade: | Crocodylomorpha |
| Clade: | Crocodyliformes |
| Family: | †Goniopholididae |
| Genus: | †Calsoyasuchus Tykoskiet al.,2002 |
| Type species | |
| †Calsoyasuchus valliceps Tykoskiet al., 2002 | |
Calsoyasuchus (meaning "[Dr. Kyril] Calsoyas'crocodile") is agenus ofcrocodylomorph[1] that lived in theEarly Jurassic. Itsfossilized remains were found in theSinemurian-Pliensbachian-ageKayenta Formation onNavajo Nation land inCoconino County,Arizona,United States. Formally described asC. valliceps, it is known from a single incomplete skull which is unusuallyderived for such an early crocodile relative. This genus was described in 2002 byRonald Tykoski and colleagues; the specific name means "valley head" and refers to a deep groove along the midline of thenasal bones andfrontal bones.[2] It has often been interpreted as the earliest diverging member ofGoniopholididae, but other studies have recovered it in various other positions.
Theholotype skull (TMM 43631-1) that would be namedCalsoyasuchus was discovered in 1997 by members of an expedition composed of crews fromTexas Memorial Museum of theUniversity of Texas at Austin, theMuseum of Comparative Zoology atHarvard University, and theSeba Dalkai Navajo Nation School. It was found in the middle third of thesiltyfacies of the Kayenta Formation, near theAdeii Eechii Cliffs. The skull is missing the lower jaws, part of thepalate, most of thesuspensorium (the bones that make up the region where the upper and lower jaws articulate), and theocciput andbraincase. 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.[2]
The skull was long, low, and curved so that both extremities were higher than the middle. Thepremaxilla bones that formed the end of the snout were enlarged to form a wide tip; there were at least four teeth in the right premaxilla and five in the left. The leftmaxilla (main tooth-bearing bone of the upper jaw) is more complete than the right, and had at least 29 teeth. There was a deep groove along the midline of the nasals and the frontals; the frontals were fused into a single bone, as is seen in other adult mesoeucrocodylians. Unlike derived neosuchians, it had externalantorbital fenestrae. Tykoski and colleagues subjected the skull toCT scanning, which revealed internal cavities and air passages, and showed that it had a double-walled secondary palate similar to that oftrue crocodylians, and similar pneumatic cavities as well.[2]
Tykoski and colleagues performed acladistic phylogenetic analysis with their newtaxon, and found that it grouped withGoniopholis,Sunosuchus, and, most closely, withEutretauranosuchus in a weakly supportedclade, Goniopholididae. They noted that the skull ofCalsoyasuchus is very similar to some goniopholid skulls from the younger,Upper JurassicMorrison Formation.Calsoyasuchus pushes back the earliest occurrence of goniopholids from the Late Jurassic into the Early Jurassic, and not only helps to bridge a temporal gap between groups of crocodyliforms, but also amorphological gap. It also implies that some groups of crocodyliforms have long undiscovered histories.[2]
In 2011,Calsoyasuchus was recovered as the basalmost goniopholidid and the sister taxon to all other goniopholidids.[3]
| Neosuchia |
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Its placement as a goniopholid is not uncontested. A cladistic analysis of Crocodylomorpha published by Wilberg et al. (2019) in their discussion of crocodylomorph paleobiology recoversCalsoyasuchus as a close relative of the basalmesoeucrocodyliformHsisosuchus.[4] A 2022 analysis found it to be the sister group ofThalattosuchia.[5]
During theSinemurian andPliensbachian ages of the Early Jurassic, the Kayenta Formation had a diversefauna, with the remains ofcaecilians,frogs,turtles, at least five other taxa ofcrocodylomorphs,pterosaurs,theropod,sauropodomorph, andornithischiandinosaurs, and early relatives of mammals (tritylodontids andmorganucodontids).[2]
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