Procyclotosaurus
Encyclopedia
Procyclotosaurus is an extinct genus
of stenotosaurid
capitosauria
n temnospondyl. The type species
is P. stantonensis. In 1904, English
paleontologist Arthur Smith Woodward
described it as a species of Capitosaurus
, 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
, a European stratigraphic unit that was deposited during the Late Triassic
. Fossils have been found from Staffordshire
, England
.
, a notch at the back of the skull, is closed. The tabular horn above the otic notch is narrow and touches the squamosal
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
(eye sockets) and nares (nostrils) that are directed upward and slightly elevated.
). 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of stenotosaurid
Stenotosauridae
Stenotosauridae is an extinct family of mastodonsauroid temnospondyls. It has included genera such as Stenotosaurus, Wellesaurus, and Procyclotosaurus....
capitosauria
Capitosauria
Capitosauria is a clade of stereospondyl temnospondyls. Capitosauria and its sister taxon Trematosauria are the only major temnospondyl clades that existed during the Mesozoic....
n temnospondyl. The type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
is P. stantonensis. In 1904, English
English people
The English are a nation and ethnic group native to England, who speak English. The English identity is of early mediaeval origin, when they were known in Old English as the Anglecynn. England is now a country of the United Kingdom, and the majority of English people in England are British Citizens...
paleontologist Arthur Smith Woodward
Arthur Smith Woodward
Sir Arthur Smith Woodward was an English palaeontologist.-Biography:Woodward was born in Macclesfield, Cheshire, England and was educated there and at Owens College, Manchester. He joined the staff of the Department of Geology at the Natural History Museum in 1882. He became assistant Keeper of...
described it as a species of Capitosaurus
Capitosaurus
Capitosaurus is an extinct genus of temnospondyl....
, 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
Keuper
The Keuper is a lithostratigraphic unit in the subsurface of large parts of west and central Europe. The Keuper consists of dolostone, shales or claystones and evaporites that were deposited during the Middle and Late Triassic epochs...
, a European stratigraphic unit that was deposited during the 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...
. Fossils have been found from Staffordshire
Staffordshire
Staffordshire is a landlocked county in the West Midlands region of England. For Eurostat purposes, the county is a NUTS 3 region and is one of four counties or unitary districts that comprise the "Shropshire and Staffordshire" NUTS 2 region. Part of the National Forest lies within its borders...
, England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
.
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 notchOtic notch
Otic notches are invagination in the posterior margin of the skull roof, one behind each orbit. Such notches are found in labyrinthodonts and some of their immediate ancestors, but not their reptilian descendants...
, a notch at the back of the skull, is closed. The tabular horn above the otic notch is narrow and touches the squamosal
Squamosal
The squamosal is a bone of the head of higher vertebrates. It is the principal component of the cheek region in the skull, lying below the temporal series and otic notch and bounded anteriorly by postorbital. Posteriorly, the squamosal articulates with the posterior elements of the palatal complex,...
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
Orbit (anatomy)
In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...
(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 MastodonsauridaeMastodonsauridae
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...
). It was later reassigned as a species of Cyclotosaurus
Cyclotosaurus
Cyclotosaurus is an extinct genus of temnospondyl within the family Mastodonsauridae....
, 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
Derived
In phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
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
Richard Owen
Sir Richard Owen, FRS KCB was an English biologist, comparative anatomist and palaeontologist.Owen is probably best remembered today for coining the word Dinosauria and for his outspoken opposition to Charles Darwin's theory of evolution by natural selection...
, and referred R 3174 to C. leptognathus.