Labyrinthodont (Greek, "maze-toothed") is an obsolete term for any member of an extinct superorder or subclass (Labyrinthodontia) of amphibians, which constituted some of the dominant animals of Late Paleozoic and Early Mesozoic times (about 350 to 210 million years ago). The name describes the pattern of infolding of the dentine and enamel of the teeth, which are often all of the creatures that survives. They are also distinguished by a heavy solid skull, and complex vertebrae, the structure of which is useful in older classifications of the group. In biology and ecology, extinction is the ceasing of existence of a species or group of taxa. ... For other uses, see Amphibian (disambiguation). ... The Paleozoic Era is a major division of the geologic timescale, one of four geologic eras. ... The Mesozoic is one of three geologic eras of the Phanerozoic eon. ... Dentin (BE: dentine) is the name of substance between the enamel (crown) or cementum (root) of a tooth and the pulp chamber. ... The word enamel can mean more than one thing: Tooth enamel Vitreous enamel Enamel (markup language) Enameled wire This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ...

Anatomy

Labyrinthodonts are named for the pattern of infolding of the dentine and enamel of the teeth, that resembles a maze (or labyrinth). Labyrinthodonts could be up to four meters long. They were short-legged and large headed. Their skulls were deep and massive, and their jaws were lined with small, sharp, conical teeth. Also, there was a second row of teeth on the roof of the mouth. In their way of living labyrinthodonts were probably similar to fishes - they laid eggs in the water, where their larvae developed into mature animals. Dentin (BE: dentine) is the name of substance between the enamel (crown) or cementum (root) of a tooth and the pulp chamber. ... The word enamel can mean more than one thing: Tooth enamel Vitreous enamel Enamel (markup language) Enameled wire This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Public hedge maze in the English Garden at Schönbusch Park, Aschaffenburg, Germany A small maze. ... A Roman mosaic showing Theseus and the Minotaur. ... A cone is a basic geometrical shape: see cone (geometry). ... Larvae are the plural of larva, juvenile form of animals with indirect development. ...

Characteristically labyrinthodonts have vertebrae made of 4 pieces, an intercentrum, two pleurocentra, and a neural arch/spine. The relative sizes of these pieces distinguishes different groups of labyrinthodonts. They also had special sense organs in the skin, that formed a system for perception of water fluctuations. Some of them possessed well developed gills and many seemingly had primitive lungs. They could breath atmospheric air; that was a great advantage for residents of warm shoals with low oxygen levels in the water. The air was inflated into the lungs by contractions of a special throat sac. Primitive members of all labyrinthodont groups were probably true water predators, and only advanced forms that arose independently in different groups and times, gained an amphibious, semi-aquatic mode of living. Their bulky skeleton and their short limbs suggest that the majority of the labyrinthodonts were slow walkers on land. A diagram of a thoracic vertebra. ... Fluctuation Fluctuation refer to an economical term called conjuncture. ... gills of a Smooth Newt Gills inside of a tuna head In aquatic organisms, gills are a respiratory organ for the extraction of oxygen from water and for the excretion of carbon dioxide. ... A shoal is a sandbank or bar creating a shallow. ...

Evolution

The Labyrinthodontia evolved from a bony fish group: the Crossopterygii rhipidistia. Nowadays only one living representative of these fish remains: the Latimeria chalumnae, which lives in the deep water in the Mozambique channel. This article is in need of attention. ... Subclasses Coelacanthimorpha - Coelacanths Dipnoi - Lungfishes Tetrapoda Sarcopterygii (from Greek sarx, flesh, and pteryx, fin) is traditionally the class of lobe-finned fishes, consisting of lungfish and coelacanths. ... Orders See text The Rhipidistia are an extinct type of lobe-finned fishes. ... Families See text Coelacanth (meaning hollow thorn, from the Greek coelia, κοιλιά (hollow) and acanthos, άκανθος (thorn)); IPA: ) is the common name for an order of fish that includes the oldest living lineage of jawed fish known to date. ... The Mozambique Channel is a portion of the Indian Ocean between the island of Madagascar and southeast Africa, namely Mozambique. ...

The most diverse group of the labyrinthodonts was the Batrachomorpha. Though these animals looked more like crocodiles, they most probably gave rise to the order Anura, the amphibians without tails, which include, in particular, the modern frogs. Batrachomorphs appeared in the Late Devonian, but they had worldwide distribution in the continental shallow basins of the Permian (Platyoposaurus, Melosaurus) and Triassic Periods (Thoosuchus, Benthosuchus, Eryosuchus). Some batrachomorphs existed until the end of the Cretaceous. Groups Temnospondyli Lissamphibia Batrachomorpha (Frog form) is a name given to recent and extinct amphibians that are not related to reptiles. ... Disambiguation: Devonian is sometimes used to refer to the Southwestern Brythonic language, and the people of the county of Devon are sometimes referred to as Devonians The Devonian is a geologic period of the Paleozoic era. ... The Permian is a geologic period that extends from about 299. ... The Triassic is a geologic period that extends from about 245 to 202 Ma (million years ago). ... The Cretaceous period is one of the major divisions of the geologic timescale, reaching from the end of the Jurassic period, about 146 million years ago (Ma), to the beginning of the Paleocene epoch of the Tertiary period (65. ...

Classification

The traditional classification (e.g. Romer 1966, also repeated in Colbert 1969, and Carroll 1988) has three orders: Alfred Sherwood Romer (December 28, 1894 _ November 5, 1973) was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution. ... Edwin H. Colbert (1905 – 2001) was a distinguished vertebrate paleontologist and prolific researcher and author. ... Robert L. Carroll (b. ...

• Ichthyostegalia (primitive ancestral forms (e.g. Ichthyostega) - Late Devonian only)
  • Now known to be basal tetrapods, not amphibians.
• Temnospondyli (common, small to large, flat-headed forms with either strong or secondarily weak vertebrae and limbs - mainly Carboniferous to Triassic e.g. Eryops from the early Permian is a well-known genus, More recently fosisl Jurassic and Cretaceous temnospondyls have been found. Originally considered ancestral to Anura (frogs), may or may not be ancestral to all modern amphibians
  • Temnospondyls are the only "Labyrinthodonts" currently considered to be true amphibians.
• Anthracosauria (deep skulls, strong vertebrae but weak limbs, evolving towards and ancestral to reptiles - Carboniferous and Permian - e.g. Seymouria)
  • Now known to be reptile-like tetrapods separate from true amphibians.

A good summary (with diagram) of characteristics and main evolutionary trends of the above three orders is given in Colbert 1969 pp.102-103. Species Ichthyostega (Greek: fish roof) is an early tetrapod genus living in the Upper Devonian (Famennian) period, 367-362. ... Groups Edopoidea Edopidae Cochleosauridae Euskelia Eryopoidea Eryopidae Zatrachydidae Dissorophoidea Limnarchia Dvinosauria Archegosauridae Stereospondyli Trematosauroidea Capitosauroidea Metoposauroidea Plagiosauroidea Rhytidosteidae Brachyopoidea Brachyopidae Chigutosauridae Temnospondyli are an important and extremely diverse taxon of small to giant labyrinthodont amphibians that flourished worldwide during the Carboniferous, Permian, and Triassic periods. ... Binomial name Eryops megacephalus Cope, 1882 Eryops (AR-ee-ops) meaning drawn-out face because most of its skull was in front of its eyes (Greek eryein = drawn-out + ops = face) is a genus of extinct, semi-aquatic amphibian found primarily in the Permian-aged Admiral Formation of Archer County... In biology, a genus (plural genera) is a taxonomic grouping. ... Groups Temnospondyli Lissamphibia Batrachomorpha (Frog form) is a name given to recent and extinct amphibians that are not related to reptiles. ... Orders Anura Caudata Gymnophiona Allocaudata The subclass Lissamphibia includes all recent amphibians. ... Groups Eoherpeton Embolomeri Gephyrostegidae Anthracosauria refers to a group of extinct reptile-like amphibians that fourished during the Carboniferous and early Permian periods, although precisely which species are included depends on ones definition of the taxon. ... Seymouria was a reptile-like tetrapod from the early Permian of Texas. ...

The grouping "Labyrinthodonts" has since been largely discarded as paraphyletic, that is, artificially composed of organisms that have separate genealogies, and thus not a valid taxon. The groups that have usually been placed within Labyrinthodontia, are currently variously classified as basal tetrapods, non-amniote Reptiliomorpha and as a monophyletic or paraphyletic Temnospondyli, according to cladistic analysis. Paraphyletic - Wikipedia /**/ @import /skins-1. ... A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). ... In phylogenetics, basal members of a group are subgroups that diverged very early from the others. ... Groups See text. ... Groups Amniota Anthracosauria Batrachosauria Chroniosuchidae Diadectomorpha Embolomeri Gephyrostegidae Seymouriamorpha Solenodonsauridae Tokosauridae Westlothiana lizziae Reptiliomorpha is a name given either to reptile-like amphibians, or to amniotes and those amphibians related to them. ... This cladogram shows the relationship among various insect groups. ...

References

• Carroll, R. L. (1988), Vertebrate Paleontology and Evolution, WH Freeman & Co.
• Colbert, E. H., (1969), Evolution of the Vertebrates, John Wiley & Sons Inc (2nd ed.)
• Romer, A. S., (1947, revised ed. 1966) Vertebrate Paleontology, University of Chicago Press, Chicago
• Comparative Vertebrate Anatomy

Robert L. Carroll (b. ... Edwin H. Colbert (1905 – 2001) was a distinguished vertebrate paleontologist and prolific researcher and author. ... Alfred Sherwood Romer (December 28, 1894 _ November 5, 1973) was an American paleontologist and comparative anatomist and a specialist in vertebrate evolution. ...

External links

• Palaeos.com Cladogram of Reptiliomorpha
• Subclass Labyrinthodontia

See also

• Tetrapod
• Temnospondyli
• Batrachosauria
• Reptiliomorpha
• Amphibian
• Prehistoric amphibian
• Ichthyostega
• Eryops
• Prehistoric life