Proterochampsidae
Encyclopedia
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
.
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.
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 archosaur
s. 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
.
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of archosauriforms. Proterochampsids may have filled an ecological niche
Ecological niche
In ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
similar to modern crocodiles, and had a general crocodile-like appearance. They lived in what is now South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
in the Middle
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...
and Late Triassic
Late Triassic
The Late Triassic is in the geologic timescale the third and final of three epochs of the Triassic period. The corresponding series is known as the Upper Triassic. In the past it was sometimes called the Keuper, after a German lithostratigraphic group that has a roughly corresponding age...
.
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
Parietal eye
A parietal eye, also known as a parietal organ or third-eye or pineal eye, is a part of the epithalamus present in some animal species...
. 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
Internal carotid artery
In human anatomy, the internal carotid arteries are two major arteries, one on each side of the head and neck. They arise from the common carotid arteries where these bifurcate into the internal and external carotid artery, and they supply the brain....
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
Tarsal
Tarsal could refer to:*tarsus *tarsus *superior tarsal muscle...
, or ankle bone. A hemicylindrical facet on the calcaneum attaches to another bone in the ankle called the astragalus
Astragalus
Astragalus is a large genus of about 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae, subfamily Faboideae. The genus is native to temperate regions of the Northern Hemisphere...
. The astragalus has facets that attach to the tibia
Tibia
The tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
and fibula that are adjacent to each other.
Classification
Proterochampsidae was named in 1966 by A.S. RomerAlfred Romer
Alfred Sherwood Romer was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution.-Biography:...
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
Proterosuchia refers to one of the suborders of Thecodontia; specifically the most primitive and ancestral forms. These were primitive, vaguely crocodile-like, archosaurs that mostly lived during the Early Triassic period....
, 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 archosaur
Archosaur
Archosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s. 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
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 :...
. Recently, the unusual Late Triassic archosauriform Doswellia
Doswellia
Doswellia is an extinct genus of archosauriform. It has been placed in its own family, Doswellidae, and its own suborder, Doswelliina. It was a terrestrial carnivore that existed in eastern North America during the Carnian stage of the Late Triassic. Fossils have been found from the Poor Farm...
has been placed as the closest relative of proterochampsids. Because doswelliids
Doswelliidae
Doswelliidae is a family of carnivore archosauriforms. Doswelliids existed in North and South America during the Middle–Late Triassic period and were among the most derived non-archosaurian archosauriforms. The family was named by R. E. Weems in 1980 and it has been placed in its own suborder,...
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
Proterochampsia
Proterochampsia is a clade of early archosauriform reptiles from the Triassic period. It includes the genera Proterochampsa, Cerritosaurus, Chanaresuchus, Gualosuchus, Rhadinosuchus, and Tropidosuchus...
. Under this classification, Cerritosaurus, Proterochampsa, and Tropidosuchus are basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
forms, while Chanaresuchus, Gualosuchus, and Rhadinosuchus form the family Rhadinosuchidae
Rhadinosuchidae
Rhadinosuchidae is an extinct family of archosauriforms. It includes the proterochampsians Gualosuchus, Chanaresuchus, and Rhadinosuchus, all of which are from the Middle and Late Triassic of Brazil. Rhadinosuchus, the type genus of the family, was originally described as a rauisuchian in 1942...
.
Genera
| Genus | Authority | Age | Location | Unit | Notes | Images |
|---|---|---|---|---|---|---|
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.... |
Price (1946) | Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma... |
 Argentina |
Santa Maria Formation Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a late Ladinian – early Carnian age , and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph... |
Assigned to Proterochampsidae by Carroll (1988) | |
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... |
Romer (1971) | Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma... |
Argentina |
Chañares Formation Chañares Formation The Chañares Formation in La Rioja Provence, Argentina, dates to the Anisian stage of the early Middle Triassic.Some localities are well known for their abundance of tetrapods. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter... |
 |
|
Gualosuchus |
Romer (1971) | Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma... |
Argentina |
Chañares Formation Chañares Formation The Chañares Formation in La Rioja Provence, Argentina, dates to the Anisian stage of the early Middle Triassic.Some localities are well known for their abundance of tetrapods. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter... |
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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... |
Reig (1959) | Norian Norian The Norian is a division of the Triassic geological period. It has the rank of an age or stage . The Norian lasted from 216.5 ± 2.0 to 203.6 ± 1.5 million years ago. It was preceded by the Carnian and succeeded by the Rhaetian.-Stratigraphic definitions:The Norian was named after the Noric Alps in... |
Argentina |
Ischigualasto Formation |
||
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... |
Huene (1942) | Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma... |
 Brazil |
Santa Maria Formation Santa Maria Formation The Santa Maria Formation is a sedimentary rock formation found in Rio Grande do Sul, Brazil. It has a late Ladinian – early Carnian age , and is notable for its fossils of early dinosaurs, including the herrerasaur Staurikosaurus, the basal saurischian Teyuwasu, and the basal sauropodomorph... |
||
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... |
Arcucci (1990) | Ladinian Ladinian The Ladinian is a stage and age in the Middle Triassic series or epoch. It spans the time between 237 ± 2 Ma and 228 ± 2 Ma... |
Argentina |
Chañares Formation Chañares Formation The Chañares Formation in La Rioja Provence, Argentina, dates to the Anisian stage of the early Middle Triassic.Some localities are well known for their abundance of tetrapods. Theraspids include the kannemeyeriid Dinodontosaurus, and cynodonts such as Probainognathus and Massetognathus, the latter... |
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