''Megalocephalus'' (meaning "big head") is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

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 baphetid animal from the late

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...

( Westphalian A-C) of the

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and 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 ...

(

Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...

). It contains two species, ''M. pachycephalus'' and ''M. lineolatus''.

History

''Megalocephalus pachycephalus''

''Megalocephalus pachycephalus'' is one of the most common large amphibians from the Carboniferous of Britain, and is known from several sites in

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 ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

, and

Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...

. The first known fossils of the genus were cranial fragments which were misattributed to ''

Rhizodus ''Rhizodus'' (root tooth) is an extinct genus of basal, finned tetrapodomorphs (the group of sarcopterygians that contains modern tetrapods and their extinct relatives). It belonged to Rhizodontida, one of the earliest-diverging tetrapodomorph c ...

'' jaw bones upon their discovery in 1864. These fragments, and many subsequent discoveries, were recovered from a quarry near Newsham,

Northumberland Northumberland () is a county in Northern England, one of two counties in England which border with Scotland. Notable landmarks in the county include Alnwick Castle, Bamburgh Castle, Hadrian's Wall and Hexham Abbey. It is bordered by land on ...

. Other ''Megalocephalus'' fossils found in the 1860s had been referred to other large amphibians, namely ''

Pteroplax ''Pteroplax'' is an extinct genus of Embolomeri, embolomerous Anthracosauria, anthracosaur. Only one species (''P. cornutus'' Hancock & Atthey, 1868) has been described; the skull table noted is the lectotype of this species. ''Pteroplax'' dates f ...

and'' ''

Anthracosaurus ''Anthracosaurus'' is an extinct genus of embolomere, a possible distant relative of reptiles that lived during the Late Carboniferous (around 310 million years ago) in what is now Scotland and England. It was a large, aquatic eel-like predator a ...

''. Two well-preserved skulls and associated jaw bones were found in Newsham in 1870 and 1871, though these were also mistakenly referred to a pre-existing genus, ''

Loxomma ''Loxomma'' (meaning “slanting eyes”) is an extinct genus of Loxommatinae and one of the first Carboniferous tetrapods. They were first described in 1862 and further described in 1870 when two more craniums were found. It is mostly associat ...

''. In 1873, Thomas P. Barkas named a pair of new genera for two more Newsham skulls. One was described as a supposed new reptile, ''Orthosaurus pachycephalus'', while the other was given the name ''Megalocephalus macromma''. ''Megalocephalus'' fossils continued to be collected in the coming decades, though most were initially referred to ''Loxomma''. "''Orthosaurus''" was re-established as a distinct genus of loxommatid amphibian by D.M.S. Watson in 1926. However, it was later determined to be a preoccupied name, and the name ''Orthosauriscus pachycephalus'' was invented and used for the rest of the early 20th century. In 1947,

Alfred Romer Alfred Sherwood Romer (December 28, 1894 – November 5, 1973) was an American paleontologist and biologist and a specialist in vertebrate evolution. Biography Alfred Romer was born in White Plains, New York, the son of Harry Houston Romer an ...

decided to rename ''Orthosauriscus pachycephalus'' to ''Megalocephalus brevicornis,'' combining Barkas' 1873 genus with ''"Pteroplax" brevicornis'', a species named for ''Megalocephalus'' fossils in 1870. However, the ''"Pteroplax" brevicornis'' fossils were poorly described and probably destroyed by a 1909 fire, so few subsequent paleontologists use Romer's combination. The modern combination ''Megalocephalus pachycephalus'' was popularized by Eileen H. Beamont's 1977 redescription of available "loxommatid" fossils.

''Megalocephalus lineolatus''

The second apparently valid species in the genus is ''Megalocephalus lineolatus''. This species is from the fossiliferous coal mine of Linton, Ohio, and was originally named as ''" Leptophractus" lineolatus'' by E.D. Cope in 1877. In the 1920s, Watson placed the species within "''Orthosaurus''", based on both Cope's specimens and new loxommatid fossils from Linton. Romer referred all Linton loxommatid material to '' Macrerpeton huxleyi''. However, later investigation revealed that Romer's conception of ''Macrerpeton'' was chimeric, including an edopoid

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 ...

(''Macrerpeton''), a loxommatid (referred to '' Baphetes''), and possibly several more species of loxommatids. Another skull described in 1957 demonstrated that ''"Leptophractus" lineolatus'' was a species of ''Megalocephalus'', as it showed several diagnostic traits of the genus.

Description

''Megalocephalus'' was an amphibian, measuring from head to tail.

Skull

It is only known from its skull, like most other baphetids. The skull of ''Megalocephalus'' was long. The teeth of ''Megalocephalus'' were long and pointed. Baphetids had a small elongation of their eye sockets, the current use of which is not certain. It has been suggested that the elongation was housing for a salt gland to get rid of excess salt, or an extra region for jaw muscle attachments, to allow a harder bite force. Like '' Kyrinion'', the lacrimal is excluded from the nares (nostrils) and the

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower tooth, teeth in place. The mandible sits beneath the maxilla. It is the only movabl ...

has large fangs. A 2009 phylogenetic analysis suggests that ''Megalocephalus'' is

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

relative to ''Kyrinion'', with ''M. pachycephalus'' closer to ''K. martilli'' than to ''M. lineolatus.'' Likewise, ''Loxomma'' forms a paraphyletic

grade Grade most commonly refers to: * Grade (education), a measurement of a student's performance * Grade, the number of the year a student has reached in a given educational stage * Grade (slope), the steepness of a slope Grade or grading may also ref ...

ancestral to ''Megalocephalus''.

References

External links

''Megalocephalus''
at the

Paleobiology Database The Paleobiology Database is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database (PBDB) originated in the NCEAS-funded Phanerozoic Marine Pale ...

Baphetoids Prehistoric animals of Asia Carboniferous animals of North America Prehistoric amphibians of North America {{Paleo-amphibian-stub