Proterochampsidae is a

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

proterochampsia Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae (e.g. ''Proterochampsa'', ''Chanaresuchus'' and ''Tropidosuchus'') and probably also the Doswelliidae. Nesbitt (2011) define ...

n archosauriforms. Proterochampsids may have filled an

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of resources and competitors (for ...

similar to modern crocodiles, and had a general crocodile-like appearance. They lived in what is now

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

in the Middle and

Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch. ...

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 a parietal foramin, which in many reptiles holds a

parietal eye A parietal eye, also known as a third eye or pineal eye, is a part of the epithalamus present in some vertebrates. The eye is located at the top of the head, is photoreceptive and is associated with the pineal gland, regulating circadian rhyth ...

. The

postorbital bone The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some v ...

s 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 In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock. ...

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 The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity i ...

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 ''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...

. The astragalus has facets that attach to the

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it connects ...

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 Proterosuchia is one of the suborders of the paraphyletic group Thecodontia; containing the most primitive and ancestral forms. These were primitive, vaguely crocodile-like, archosauriforms that mostly lived during the Early Triassic epoch. The ...

, another group of long-snouted Triassic archosauriforms. As

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

studies became more common in the 1980s and 1990s, proterochampsids were found to be a distinct group closely related to true archosaurs. Recent studies have placed Proterochampsidae as either the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...

of Archosauria (the closest relatives of archosaurs), or the sister taxon of Archosauria and ''

Euparkeria ''Euparkeria'' (; meaning "Parker's good animal", named in honor of W.K. Parker) is an extinct genus of archosauriform from the Middle Triassic of South Africa. It was a small reptile that lived between 245-230 million years ago, and was close to ...

''. In a 2011 study, the unusual Late Triassic archosauriform ''

Doswellia ''Doswellia'' is an extinct genus of archosauriform from the Late Triassic of North America. It is the most notable member of the family Doswelliidae, related to the proterochampsids. ''Doswellia'' was a low and heavily built carnivore which liv ...

'' 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''. Modern studies place Proterochampsids in a larger group called

Proterochampsia Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the Proterochampsidae (e.g. ''Proterochampsa'', ''Chanaresuchus'' and ''Tropidosuchus'') and probably also the Doswelliidae. Nesbitt (2011) define ...

. Under the classification of Kischlat and Schultz (1999), ''Cerritosaurus'', ''Proterochampsa'', and ''Tropidosuchus'' are basal forms, while ''Chanaresuchus'', ''Gualosuchus'', and ''Rhadinosuchus'' form the family Rhadinosuchidae. However, more recent studies reduce Rhadinosuchidae to a subfamily level as Rhadinosuchinae to be placed within Proterochampsidae and include advanced proterochampsid, e.g. ''Chanaresuchus'' and ''Rhadinosuchus''. Below is a

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

following the phylogenetic analysis of Ezcurra (2016) that recovered Doswelliidae as the sister taxon of Proterochampsidae (within

). Proterochampsia was found to be the sister taxon of Archosauria, whose living representatives consist of

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s and

crocodilia Crocodilia (or Crocodylia, both ) is an order of mostly large, predatory, semiaquatic reptiles, known as crocodilians. They first appeared 95 million years ago in the Late Cretaceous period ( Cenomanian stage) and are the closest livi ...

ns.

Genera

Sources

* A. S. Romer. 1966. ''Vertebrate Paleontology'', 3rd edition. University of Chicago Press, Chicago 1-468 . Uhen/M. Uhen/M. Carrano {{Taxonbar, from=Q599138 Proterochampsians Prehistoric reptile families Triassic reptiles of South America Ladinian first appearances Norian extinctions Taxa named by Alfred Romer