''Camposaurus'' ( ) is a

coelophysid Coelophysidae is a family of primitive carnivorous theropod dinosaurs. Most species were relatively small in size. The family flourished in the Late Triassic and Early Jurassic periods, and has been found on numerous continents. Many members of C ...

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

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

from the

Norian The Norian is a division of the Triassic Period. It has the rank of an age (geochronology) or stage (chronostratigraphy). It lasted from ~227 to million years ago. It was preceded by the Carnian and succeeded by the Rhaetian. Stratigraphic defi ...

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 ...

period of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

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

stage, and is widely regarded as the oldest known

neotheropod Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the e ...

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 is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

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 (; ), 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 ...

that fits with 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 is ...

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

condyle A condyle (;Entry "condyle"
in
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

type species In 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 species that contains the biological type specimen ...

, ''C. arizonensis'', was formally named and described by Adrian Hunt,

Spencer G. Lucas Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fossils ...

, Andrew B. Heckert,

Robert M. Sullivan Robert Michael "Bob" Sullivan (born August 4, 1951) is a Vertebrate_paleontology, vertebrate paleontologist, noted for his work on fossil lizards and Dinosaur, dinosaurs. Sullivan discovered the second and most complete skull of the Hadrosaurid ...

and

Martin Lockley Martin G. Lockley (born 1950) is a Welsh palaeontologist. He was educated in the United Kingdom where he obtained degrees (BSc and PhD) and post-doctoral experience in Geology in the 1970s. Since 1980 he has been a professor at the Universit ...

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 Jamestown, North Dakota – August 14, 1975 San Jose, California) was a palaeontologist and zoologist, working from the University of California, Berkeley. He took part in excavations at the 'Placerias Quarry', in ...

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

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

, in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

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 (230–220 million years ago). ''Placerias'' belongs to a group of dicynodonts called Kannemeyeriiforme ...

'' 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 ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

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

dinosaur. ''Camposaurus'' was originally placed in the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

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 earliest ...

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'' ( traditionally; or , as heard more commonly in recent decades) is an extinct genus of coelophysid theropod dinosaur that lived approximately 228 to 201.3 million years ago during the latter part of the Triassic Period from t ...

''. 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 ''Megapnosaurus'' (meaning "big dead lizard", from Greek μεγα = "big", 'απνοος = "not breathing", "dead", σαυρος = "lizard") is an extinct genus of coelophysid Theropoda, theropod dinosaur that lived approximately 188 million yea ...

''. 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 s ...

''. A reassessment of the holotype UCMP 34498 of ''Camposaurus arizoniensis'' by Ezcurra and Brusatte revealed two

autapomorphies In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to t ...

, thereby firmly establishing this material as a valid genus and species. This analysis also demonstrated that ''Camposaurus'' is definitely a

, 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 ''Meganosaurus, 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

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 ...

is without a strong cranial projection of the medial

condyle A condyle (;Entry "condyle"
in
Coelophysoids Late Triassic dinosaurs of North America Triassic Arizona Paleontology in Arizona Fossil taxa described in 1998 Taxa named by Spencer G. Lucas Taxa named by Robert M. Sullivan Taxa named by Martin Lockley