Proterochampsia is a clade

Clade

A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...

 of early archosauriform reptile

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s from the Triassic

Triassic

The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 period. It includes the genera Proterochampsa

Proterochampsa

Proterochampsa is a genus of proterosuchid archosauromorph from the Late Triassic of Argentina.-Sources:* The Beginning of the Age of Dinosaurs: Faunal Change across the Triassic-Jurassic Boundary by Kevin Padian...

, Cerritosaurus

Cerritosaurus

Cerritosaurus is a genus of proterochampsid archosauromorph from the Upper Triassic. It has been found in the Santa Maria Formation, in the Geopark of Paleorrota. It is represented by one species....

, Chanaresuchus

Chanaresuchus

Chanaresuchus is an extinct genus of proterochampsian archosauriform. It was of modest size for a proterochampsian, being on average just over a meter in length. Fossils have been found from the Chañares Formation in La Rioja Provence, Argentina, dating back to the Ladinian stage of the Middle...

, Gualosuchus, Rhadinosuchus

Rhadinosuchus

Rhadinosuchus is an extinct genus of proterochampsian archosauriform reptile from the Late Triassic. It is known only from the type species Rhadinosuchus gracilis. It is reposited in Munich. The fossil has the form of an incomplete skull and fragments of post-cranial material...

, and Tropidosuchus

Tropidosuchus

Tropidosuchus is an extinct genus of carnivorous archosauriform from the Middle Triassic period . It is a proterochampsid which lived in what is now Argentina. It is known from the holotype PVL 4601, which consists of partial skeleton. It was found in the Chañares Formation and its type locality is...

. Nesbitt (2011) defines Proterochampsia as a stem-based taxon that includes Proterochampsa

Proterochampsa

Proterochampsa is a genus of proterosuchid archosauromorph from the Late Triassic of Argentina.-Sources:* The Beginning of the Age of Dinosaurs: Faunal Change across the Triassic-Jurassic Boundary by Kevin Padian...

and all forms more closely related to it than Euparkeria

Euparkeria

Euparkeria was a small African reptile of the early Triassic period between 248-245 million years ago, close to the ancestry of the archosaurs.- Palaeobiology :...

, Erythrosuchus

Erythrosuchus

Erythrosuchus is an extinct genus of archosauriform reptile from the Triassic of South Africa and Namibia. Remains have been found from the Cynognathus Assemblage Zone of the Beaufort Group in the Karoo of South Africa as well as the Omingonde Formation in Namibia.Erythrosuchus was the largest...

, Passer domesticus (the House Sparrow), or Crocodylus niloticus (the Nile crocodile).

Proterochampsians share several distinguishing characteristics, or synapomorphies. A prominent ridge runs along the length of the jugal

Jugal

The jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....

, a bone below the eye. Another ridge is present on the quadratojugal

Quadratojugal

The quadratojugal is a small jaw bone that is present in most amphibians, reptiles, and birds, but has been lost in mammals. It is connected to the jugal as well as other bones, though these may vary with species....

, a bone positioned toward the back of the skull behind the jugal. There is also a depression on the squamosal

Squamosal

The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...

 bone of the skull roof

Skull roof

The skull roof , or the roofing bones of the skull are a set of bones covering the brain, eyes and nostrils in bony fishes and all land living vertebrates. The bones are derived from dermal bone, hence the alternative name dermatocranium...

. The second metatarsal of the foot is wider than the other metatarsals. Proterochampsians lack a fifth digit on the foot; the fifth metatarsal is reduced to a small pointed bone.

Below is a cladogram

Cladogram

A cladogram is a diagram used in cladistics which shows ancestral relations between organisms, to represent the evolutionary tree of life. Although traditionally such cladograms were generated largely on the basis of morphological characters, DNA and RNA sequencing data and computational...

 showing the phylogenetic relationships of proterochampsians from Kischlat and Schultz (1999):