Proterochampsidae

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Proterochampsidae Temporal range: Middle - Late Triassic, 237–216 Ma PreЄ Є Є O O S S D D C C P P T T J J K K Pg Pg N N
File:Proterochampsa BW.jpg
Life restoration of Proterochampsa
Scientific classification
Unrecognized taxon (fix):	Proterochampsidae
Genera
Barberenachampsa (Barberena, 1982) Cerritosaurus (Price, 1946) Chanaresuchus (Romer, 1971) Gualosuchus (Romer, 1971) Proterochampsa (Reig, 1959) Tropidosuchus (Arcucci, 1990)

Proterochampsidae is a family of archosauriforms. Proterochampsids may have filled an ecological niche similar to modern crocodiles, and had a general crocodile-like appearance. They lived in what is now South America in the Middle and Late Triassic.

Description

Proterochampsids have long, crocodile-like skulls. The posterior portion of the skull is wide while the snout is very narrow. Most proterochampsids also have downturned snouts. Like many early archosauriforms, they also have dermal armour.

Proterochampsids have small holes called dorsal fenestrae at the top of their skulls. Unlike other early archosauromorphs, they do not have parietal foramina, which in many reptiles holds a parietal eye. The postorbital bones behind the eye sockets have thick, jagged crests. As another diagnostic feature of the group, the holes that allow the passage of the internal carotid artery through the braincase open at the sides of a bony projection called the basipterygoid process. Proterochampsids are primitive in that they have simple plate-like pelvises, but they lack small bones in the vertebra called intercentra that are common in earlier reptiles.

As in most archosaurs, distinguishing features can be seen in the shape of the ankle bones. A projection on the calcaneum bone called the calcaneal tuber is narrow and positioned downward relative to other lateral projections on the bone. The calcaneum also has a facet that attaches to both the fibula bone of the leg and another tarsal, or ankle bone. A hemicylindrical facet on the calcaneum attaches to another bone in the ankle called the astragalus. The astragalus has facets that attach to the tibia and fibula that are adjacent to each other.

Classification

Proterochampsidae was named in 1966 by A.S. Romer in his book Vertebrate Paleontology, 3rd edition. Members such as Proterochampsa and Cerritosaurus had been known for several decades prior to the family's creation. Proterochampsids were originally thought to be close relatives of crocodilians based on their similar appearance. In the following years, proterochampsids were frequently associated with Proterosuchia, another group of long-snouted Triassic archosauriforms. As phylogenetic studies became more common in the 1980s and 1990s, proterochapsids were found to be a distinct group closely related to true archosaurs. Recent studies have placed Proterochampsidae as either the sister taxon of Archosauria (the closest relatives of archosaurs), or the sister taxon of Archosauria and Euparkeria. Recently, the unusual Late Triassic archosauriform Doswellia has been placed as the closest relative of proterochampsids. Because doswelliids are more closely related to proterochampsids than to any other archosauriform, the two groups form their own clade.

Seven species have been assigned to Proterochampsidae: Cerritosaurus binsfeldi, Chanaresuchus bonapartei, Gualosuchus reigi, Rhadinosuchus gracilis, Tropidosuchus romeri, Proterochampsa barrionuevoi, and Proterochampsa nodosa. P. nodosa was assigned to its own genus Barberenachampsa in 2000, but it is generally still considered to be a species of Proterochampsa. Proterochampsids have occasionally been placed in a larger group called Proterochampsia. Under this classification, Cerritosaurus, Proterochampsa, and Tropidosuchus are basal forms, while Chanaresuchus, Gualosuchus, and Rhadinosuchus form the family Rhadinosuchidae.

Genera

Genus	Authority	Age	Location	Unit	Notes	Images
Cerritosaurus	Price (1946)	Ladinian	Template:Country data Argentina	Santa Maria Formation	Assigned to Proterochampsidae by Carroll (1988)
Chanaresuchus	Romer (1971)	Ladinian	Template:Country data Argentina	Chañares Formation		File:Chanaresuchus.jpg
Gualosuchus	Romer (1971)	Ladinian	Template:Country data Argentina	Chañares Formation
Proterochampsa	Reig (1959)	Norian	Template:Country data Argentina	Ischigualasto Formation
Rhadinosuchus	Huene (1942)	Ladinian	Template:Country data Brazil	Santa Maria Formation
Tropidosuchus	Arcucci (1990)	Ladinian	Template:Country data Argentina	Chañares Formation

References

• A. S. Romer. 1966. Vertebrate Paleontology, 3rd edition. University of Chicago Press, Chicago 1-468 [M. Uhen/M. Uhen/M. Carrano]

External links

• Proterochampsidae on Palaeos
• Taxon on Mikko's Phylogeny Archive
• On the Checklist on Non-Avian DInosaurs
• On Biolib
• On the Paleobiology Database
• Page on Italian Wikipedia
• Page on Basal Archosaurs

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