''Camposaurus'' ( ) is a

coelophysid Coelophysoidea is an extinct clade of theropod dinosaurs common during the Late Triassic and Early Jurassic periods. They were widespread geographically, probably living on all continents. Coelophysoids were all slender, carnivore, carnivorous fo ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

from the

Norian The Norian is a division of the Triassic geological period, Period. It has the rank of an age (geology), age (geochronology) or stage (stratigraphy), stage (chronostratigraphy). It lasted from ~227.3 to Mya (unit), million years ago. It was prec ...

stage of the

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

period of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

. The pertinent fossil remains date back to the early to middle

stage, and is widely regarded as the oldest known neotheropod.

Description

''Camposaurus'' is a small, carnivorous, theropod dinosaur. Its approximate length and weight cannot be reliably estimated because of the sparse material that is known from this genus. ''Camposaurus'' is known from partial lower leg bones,

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

UCMP 34498 (which includes distal tibiae, distal fibulae, and astragalocalcanea), and other fragmentary material. Like other

s, it has fused tibio-tarsals and fibulo-tarsals. Unlike its relatives, the area of the

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

that fits with the

fibula The fibula (: fibulae or fibulas) 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. ...

has a distinct ridge at the back. Another unique feature is the lack of a large medial

condyle A condyle (;Entry "condyle"
in

on the

astragalus Astragalus may refer to: * ''Astragalus'' (plant), a large genus of herbs and small shrubs *Astragalus (bone) The talus (; Latin for ankle or ankle bone; : tali), talus bone, astragalus (), or ankle bone is one of the group of foot bones known ...

. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

, ''C. arizonensis'', was formally named and described by Adrian Hunt, Spencer G. Lucas, Andrew B. Heckert, Robert M. Sullivan and Martin Lockley in 1998.A.P. Hunt, S.G. Lucas, A.B. Heckert, R.M. Sullivan and M.G. Lockley, 1998, "Late Triassic dinosaurs from the western United States", ''Géobios'' 31(4): 511-531 The genus name means "Camp's lizard", after

Charles Lewis Camp Charles Lewis Camp (March 12, 1893 – August 14, 1975) was an American Palaeontology, palaeontologist and Zoology, zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in 1930 and ...

. The species name refers to the fact it was found in

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

Discovery

The

specimen UCMP 34498 was discovered in the ''

Placerias ''Placerias'' (meaning 'broad body') is an extinct genus of dicynodonts that lived during the Carnian to the Norian age of the Triassic Period (geology), Period (230–215 million years ago). ''Placerias'' belongs to a group of dicynodonts called ...

'' quarry of the

Bluewater Creek Formation The Bluewater Creek Formation is a geologic formation in west-central New Mexico. It preserves fossils dating back to the late Triassic period. Description The formation consists of red sandstones and mudstones and has a total thickness in exce ...

of Arizona, from the

stage of the Late

Triassic The Triassic ( ; sometimes symbolized 🝈) is a geologic period and system which spans 50.5 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.4 Mya. The Triassic is t ...

period in 1934, It wasn't named until 1998 by Hunt and colleagues. Hunt ''et al.'' included many remains also from ''Placerias'' quarry as paratypes, but due to the lack of association in the large bonebed, this was disregarded.

Classification

''Camposaurus'' is considered to be one of the oldest, if not the oldest, known neotheropod dinosaur. ''Camposaurus'' was originally placed in the

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Ceratosauria Ceratosaurs are members of the clade Ceratosauria, a group of dinosaurs defined as all theropods sharing a more recent common ancestor with '' Ceratosaurus'' than with birds. The oldest known ceratosaur, '' Saltriovenator'', dates to the earlies ...

based on the analysis of Long and Murray (1995). It is morphologically similar to, and was incorrectly considered for some time to be a species of, ''

Coelophysis ''Coelophysis'' ( Traditional English pronunciation of Latin, traditionally; or , as heard more commonly in recent decades) is a genus of coelophysid Theropoda, theropod dinosaur that lived Approximation, approximately 215 to 201.4 million y ...

''. In 2000, Downs examined ''Camposaurus'' and concluded that it is a junior synonym of ''

'', because of its similarity to some of the ''Coelophysis'' Ghost Ranch specimens. The review by Nesbitt et al. in 2007, revealed that a specific feature of the ankle (the ventral astragalar margin) was found to be straight, and is indistinguishable from that of ''Coelophysis bauri.'' Based on this Nesbitt ''et al.'' (2007) concluded that the two genera were synonymous.Nesbitt, Irmis and Parker, 2007. A critical re-evaluation of the Late Triassic dinosaur taxa of North America. Journal of Systematic Palaeontology. 5(2), 209–243. In 2011, it was entered into a phylogenetic analysis and found to be a close relative of '' Megapnosaurus rhodesiensis''. The lack of material has led many paleontologists to reject it as a ''

nomen dubium In binomial nomenclature, a ''nomen dubium'' (Latin for "doubtful name", plural ''nomina dubia'') is a scientific name that is of unknown or doubtful application. Zoology In case of a ''nomen dubium,'' it may be impossible to determine whether a ...

''. A reassessment of the holotype UCMP 34498 of ''Camposaurus arizoniensis'' by Ezcurra and Brusatte revealed two autapomorphies, thereby firmly establishing this material as a valid genus and species. This analysis also demonstrated that ''Camposaurus'' is definitely a neotheropod, and based on phylogenetic analysis its closest known relative is ''Megapnosaurus rhodesiensis'', because they share similarities in the

, and ankle. The synonymy with ''Coelophysis'' was found to be unsupported in 2017 when in a phylogenetic analysis by Ezcurra, ''Camposaurus'' was found to be in a clade with ''Megapnosaurus, Segisaurus'', and also ''Lucianovenator'' by Martinez & Apaldetti later that year.Ricardo N. Martínez and Cecilia Apaldetti (2017). A Late Norian–Rhaetian coelophysid neotheropod (Dinosauria, Saurischia) from the Quebrada del Barro Formation, northwestern Argentina. Ameghiniana 54: 488–505.

Distinguishing anatomical features

A diagnosis is a statement of the anatomical features of an organism (or group) that collectively distinguish it from all other organisms. Some, but not all, of the features in a diagnosis are also autapomorphies. An autapomorphy is a distinctive anatomical feature that is unique to a given organism or group. According to Ezcurra and Brusatte (2011), ''Camposaurus'' can be distinguished based on the following features: * the caudal ridge of the

articular surface on the

is prominent, taking the form of a sharp longitudinal ridge, the medial surface having a strongly developed, rostrally bowed, diagonal tuberosity * the

is without a strong cranial projection of the medial

condyle A condyle (;Entry "condyle"
in

of the astragalar body, resulting in a sub-rectangular astragalar body in the distal aspect, and a ventral margin that is incipiently concave in the cranial aspect

References

{{Taxonbar, from=Q29057464 Coelophysoidea Dinosaur genera Norian dinosaurs Chinle Formation Fossil taxa described in 1998 Taxa named by Spencer G. Lucas Taxa named by Robert M. Sullivan Taxa named by Martin Lockley Dinosaurs of the United States