''Procyclotosaurus'' is an extinct

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 ...

of stenotosaurid

capitosauria Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts t ...

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...

. 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 ...

is ''P. stantonensis''. In 1904,

English English usually refers to: * English language * English people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ide ...

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Arthur Smith Woodward Sir Arthur Smith Woodward, FRS (23 May 1864 – 2 September 1944) was an English palaeontologist, known as a world expert in fossil fish. He also described the Piltdown Man fossils, which were later determined to be fraudulent. He is not relate ...

described it as a species of ''

Capitosaurus ''Capitosaurus'' is an extinct genus of temnospondyl amphibians whose remains have been found in Spitsbergen and Germany. Its skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cra ...

'', ''C. stantonensis'', based on a partial skull known as R 3174. In 1958, the species was assigned to the new genus. It is known from the Lower

Keuper The Keuper is a lithostratigraphic unit (a sequence of rock strata) in the subsurface of large parts of west and central Europe. The Keuper consists of dolomite, shales or claystones and evaporites that were deposited during the Middle and Late ...

, a European stratigraphic unit that was deposited during the late Middle Triassic.Witzmann, Florian & Sachs, Sven & Nyhuis, Christian. (2016). A new species of Cyclotosaurus (Stereospondyli, Capitosauria) from the Late Triassic of Bielefeld, NW Germany, and the intrarelationships of the genus. Fossil Record. 19. 83-100. 10.5194/fr-19-83-2016. Fossils have been found from

Staffordshire Staffordshire (; postal abbreviation Staffs.) is a landlocked county in the West Midlands region of England. It borders Cheshire to the northwest, Derbyshire and Leicestershire to the east, Warwickshire to the southeast, the West Midlands Cou ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

Description

''Procyclotosaurus'' was a relatively small temnospondyl. Unlike most other capitosaurs, which have wide and flat skulls, ''Procyclotosaurus'' has a deep, wedge-shaped skull. The

otic notch Otic notches are invaginations in the posterior margin of the skull roof, one behind each orbit. Otic notches are one of the features lost in the evolution of amniotes from their tetrapod ancestors. The notches have been interpreted as part of an ...

, a notch at the back of the skull, is closed. The tabular horn above the otic notch is narrow and touches the

squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone. In most tetrapods, the squamosal and quadratojugal The quadratojugal is a skull bone present in many vertebrates, including ...

bone below the notch. The upper surface of the skull is concave, making it appear dish-shaped. Like other capitosaurs, ''Procyclotosaurus'' resembles

crocodilian 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 living ...

s in that it has

orbits In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

(eye sockets) and nares (nostrils) that are directed upward and slightly elevated.

History and classification

''Procyclotosaurus stantonensis'' was first classified as a species of ''Capitosaurus'' and was placed in the family Capitosauridae (now known as

Mastodonsauridae Mastodonsauridae is a family of capitosauroid temnospondyls. Fossils belonging to this family have been found in North America, Greenland, Europe, Asia, and Australia. The family Capitosauridae is synonymous with Mastodonsauridae. Description S ...

). It was later reassigned as a species of ''

Cyclotosaurus ''Cyclotosaurus'' is an extinct genus of temnospondyl within the family Mastodonsauridae. It was of great size for an amphibian, had an elongated skull up to . Etymology The name means "round eared lizard" in Ancient Greek, derived from round ...

'', another mastodonsaurid genus. In 1958, paleontologist D.M.S. Watson placed the species in its own genus, ''Procyclotosaurus'', distinguishing it from both ''Capitosaurus'' and ''Cyclotosaurus'' on the basis of its deep skull. Watson also found the short suture between the exoccipital and pterygoid bones to be characteristic of the genus. He also noted that ''Procyclotosaurus'' has a crista obliqua, or oblique ridge, on the pterygoid bone at the back of the skull. This ridge is a primitive feature among temnospondyls that is not seen in more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

mastodonsaurids. The holotype of ''Procyclotosaurus'', R 3174, is thought to be a young adult. The sutures between the bones of the skull are clearly visible and have not fully closed. The skull is pitted and some of the pits have elongated into troughs, a sign of age. However, these troughs are not as prominent as they would be in an older individual. Paleontologist Roberta L. Paton considered the deep skull and close-set eyes of ''Procyclotosaurus'' to be indicative of a young ''Cyclotosaurus'' individual rather than a distinct genus. Therefore, in 1974, Paton reassigned ''Procyclotosaurus stantonensis'' to ''Cyclotosaurus''. Paton also considered ''C. stantonensis'' to be synonymous with the species ''C. leptognathus'', named by English paleontologist

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Owe ...

, and referred R 3174 to ''C. leptognathus''.

References

Triassic temnospondyls of Europe Prehistoric amphibian genera {{temnospondyli-stub