''Procyclotosaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

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 ...

temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive amphibians—that flourished worldwide during the Carbo ...

. 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 specime ...

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 T ...

, 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,

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 a ...

, 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 bones form the cheek series of the skull. The bone forms an ancestral co ...

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

). It was later reassigned as a species of '' Cyclotosaurus'', 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 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, and referred R 3174 to ''C. leptognathus''.

References

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