''Crassigyrinus'' (from la, crassus, 'thick' and el, γυρίνος el, gyrínos, 'tadpole') 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 carnivorous stem tetrapod from the

Early Carboniferous Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * ...

Limestone Coal Group of

Scotland Scotland (, ) is a Countries of the United Kingdom, country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a Anglo-Scottish border, border with England to the southeast ...

and possibly Greer, West Virginia. The type specimen was originally described as ''Macromerium scoticum'' and lacked a complete

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...

. With subsequent discoveries, ''Crassigyrinus'' is now known from three skulls, one of which is in articulation with a fairly complete skeleton, and two incomplete lower jaws. ''Crassigyrinus'' grew up to 2 meters in length, coupled with tiny limbs and unusually large jaws. ''Crassigyrinus'' is taxonomically enigmatic, having confused

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 ...

s for decades with its apparent

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of ...

-like and tetrapod features.Chapter on ''Crassigyrinus''
from ''Gaining ground: the origin and evolution of tetrapods'', '' by Jennifer A. Clack, Indiana University Press 2002, from

Google Books Google Books (previously known as Google Book Search, Google Print, and by its code-name Project Ocean) is a service from Google Inc. that searches the full text of books and magazines that Google has scanned, converted to text using optical ...

It was traditionally placed within the group

Labyrinthodontia "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major components of ecosystems in the late Paleozoic and early Mesozoic eras (about 390 to 150 million years ago). Traditionally consi ...

along with many other early tetrapods. Some paleontologists have even considered it as the most basal crown group tetrapod, while others hesitate to even place it within the Tetrapoda superclass. ''Crassigyrinus'' had unusually large jaws, enabling it to eat other animals it could catch and swallow. It had two rows of sharp

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, t ...

in its jaws, the second row having a pair of fangs. ''Crassigyrinus'' had large eyes, suggesting that it was either nocturnal, or lived in very murky water.

Description

''Crassigyrinus'' had a streamlined body up to 2 meters in length. Its limbs were tiny and virtually useless, implying that the animal was almost completely aquatic. ''Crassigyrinus'' had unusually large jaws, equipped with two rows of sharp

, the second row having a pair of palatal fangs. Studies have shown that ''Crassigyrinus'' may have been able to open its mouth as wide as 60 degrees, which suggests that it was a powerful predator with a strong bite. This strongly suggests that it was ideally suited for catching fish, and the animal was probably a fast-moving predator. Several thickened bony ridges ran along the dorsal midline of the snout and between the eyes, and several paleontologists have suggested that they helped the

to withstand stress when the animal bit prey. ''Crassigyrinus'' had large eyes, suggesting that it was either nocturnal, or lived in very murky water. It possessed large otic (spiracular) notches, probably accommodating a spiracle rather than a tympanic membrane. Its peculiar stunted forelimbs were tiny and the humerus was only 35 mm long (the whole animal was about 1.5 m long). Various

foramina In anatomy and osteology, a foramen (;Entry "foramen"
in

on the humeral surfaces are very similar to those seen in '' Ichthyostega'', ''

Acanthostega ''Acanthostega'' (meaning "spiny roof") is an extinct genus of stem-tetrapod, among the first vertebrate animals to have recognizable limbs. It appeared in the late Devonian period (Famennian age) about 365 million years ago, and was anatomic ...

'', and

lobe-finned fish Sarcopterygii (; ) — sometimes considered synonymous with Crossopterygii () — is a taxon (traditionally a class or subclass) of the bony fishes known as the lobe-finned fishes. The group Tetrapoda, a mostly terrestrial superclass includ ...

es like ''

Eusthenopteron ''Eusthenopteron'' (from el, εὖ , 'good', el, σθένος , 'strength', and el, πτερόν 'wing' or 'fin') is a genus of prehistoric sarcopterygian (often called lobe-finned fishes) which has attained an iconic status from its close ...

''.Panchen, A. L. 1985. On the amphibian ''Crassigyrinus scoticus'' Watson from the Carboniferous of Scotland. ''Philosophical Transactions of the Royal Society of London B'' 309, 505-568.Panchen, A. L. 1991. The early

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s: classification and the shapes of cladograms. In Schultze, H.-P. & Trueb, L. (eds) ''Origins of the Higher Groups of Tetrapods, Controversy and Consensus''. Comstock/Cornell University Press (Ithaca and London), pp. 110-144. The hindlimbs were much larger than the forelimbs, and in the pelvis the ilium lacked a bony connection to the vertebral column (a classic feature of aquatic tetrapods). Although there is evidence that the Crassigyrinus eventually lost its limbs, there is counterevidence in that it used its limbs for movement, as proven by healing in the bones in case of injury. The fact that there is a need to heal the limbs must mean there was an importance of the limbs at some point, and was then lost. The tail, only known from a few vertebrae fragments, is assumed to have been long and laterally compressed.

References

External links

Crassigyrinus
{{Taxonbar, from=Q134235 Stegocephalians Basal tetrapods of Europe Paleozoic amphibians of Europe Carboniferous amphibians Carboniferous Scotland Viséan life Fossils of Scotland Fossil taxa described in 1929