Temnospondyli are an important and extremely diverse taxon of small to giant labyrinthodont amphibians that flourished worldwide during the Carboniferous, Permian, and Triassic periods. A few stragglers continued into the Cretaceous. During their evolutionary history they adapted to a very wide range of habitats, including fresh-water aquatic, semi-aquatic, amphibious, terrestrial, and in one group even near-shore marine, and their fossil remains have been found on every continent. Authorities disagree (Benton 2000, 2004, Laurin 1996, Reisz no date), over whether some specialised forms were ancestral to some modern amphibians, or whether the whole group died out without leaving any descendents. Scientific classification or biological classification is how biologists group and categorize extinct and living species of organisms. ... Binomial name Aptenodytes forsteri Gray, 1844 For other uses, see Animal (disambiguation). ... Typical Classes Subphylum Urochordata - Tunicatas Ascidiacea Thaliacea Larvacea Subphylum Cephalochordata - Lancelets Subphylum Myxini - Hagfishes Subphylum Vertebrata - Vertebrates Petromyzontida - Lampreys Placodermi (extinct) Chondrichthyes - Cartilaginous fishes Acanthodii (extinct) Actinopterygii - Ray-finned fishes Actinistia - Coelacanths Dipnoi - Lungfishes Amphibia - Amphibians Reptilia - Reptiles Aves - Birds Mammalia - Mammals Chordates (phylum Chordata) include the vertebrates, together with... Classes Synapsida Sauropsida Amphibia A tetrapod (Greek tetrapoda, four-legged) is a vertebrate animal having four feet, legs or leglike appendages. ... For other uses, see Amphibian (disambiguation). ... Dylan Byrne(September 25, 1839 - January 5, 1904), German palaeontologist, was born at Bahlingen in Baden. ... 1888 (MDCCCLXXXVIII) is a leap year starting on Sunday (click on link for calendar) of the Gregorian calendar or a leap year starting on Tuesday of the Julian calendar. ... Families Eryopidae Parioxyidae Zatracheidae Eryopoidea are a taxon of late Carboniferous and Permian temnospondyli amphibians, known from North America and Europe. ... Genera Eryops Chelyderpeton Clamorosaurus Onchiodon Osteophorus Sclerocephalus Syndyodosuchus Eryopidae are a family of medium to large Permian temnospondyli amphibians, known from North America and Europe, of which the best known form is the large species Eryops megacephalus. ... Genera Dissorophidae Trematopsidae Doleserpeton Micropholis Tersomius Dissorophoidea are a clade of medium-sized, temnospondyl amphibians that appeared during the Late Pennsylvanian in Euramerica, and continued through to trhe late Permian and even possibly the Early Triassic of Gondwana (if Micropholis belongs here). ... A taxon (plural taxa), or taxonomic unit, is a grouping of organisms (named or unnamed). ... A Labyrinthodont (Greek, maze-toothed) is any member of an extinct suborder (Labyrinthodontia) or subclass of amphibians that constituted the dominant animals of Late Paleozoic and Early Mesozoic times (about 350 to 210 million years ago). ... Orders Subclass Labyrinthodontia- extinct Subclass Lepospondyli- extinct Subclass Lissamphibia   Anura   Caudata   Gymnophiona Amphibians (class Amphibia) are a taxon of animals that include all tetrapods (four-legged vertebrates) that do not have amniotic eggs. ... The Carboniferous is a major division of the geologic timescale that extends from the end of the Devonian period, about 359. ... 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

Two types of Vertebrae

Originally, Temnospondyls were classified according to the structure of the vertebrae. Earlier forns, with complex vertebrae consisting of a number of separate elements, were called "Rachitomi", and large Triassic aquatic forms with simpler and more degenerate vertebrae were called "Stereospondyli"; and these two types were considered suborders of the order Temnospondyli. A diagram of a thoracic vertebra. ...

In the Ratchitomous condition the intercentra were large and wedge-shaped, and the pleuracentra were relatively small blocks that fitted between them. Both elements supported the neural arch, and there were well developoed and interlocking zygapophyses that strengthened the connections between the vertebrae. The strong backbone, plus strong limbs, enabled many ratchitomes to be at least partially, and in some cases fully, terrestrial. A zygapophysis is process which sticks out of an end of a vertebra to lock with a zygapophysis on the next vertebra, to make the backbone more stable. ...

In the stereospondylous condition the pleurocentra have been lost, and the veretbral centra reduced to simple blocks made up of the intercentra only. This weaker type of backbone indicates a more fully aquatic existence (Colbert 1969)

Cladistic Research

More recently, cladistic research shows that this classification is no longer viable. The basic Ratchitomous condition is primitive for amphibians (tetrapods) in general, the pure stereospondyls seem to have arisen from different ancestors (Carroll 1988), although a broader definition considers a monophyletic clade (Yates and Warren 2000, Laurin and Steyer 2000), and some temnospondyls have ratchitomous, semi-ratchitomous, and sterospondylous vertebrae at different points the vertebral column if the same individual, and some taxa show intermediate morphologies that don't fit into one or the other category (Steyer and Laurin 2000). Groups See text. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... A clade is group of organisms which share a common ancestor and which includes all decendents of that ancestor. ...

Evolutionary History

During the Carboniferous, Temnospondyls included primitive medium-sized (Dendrerpeton) or large (Cochleosaurus about 1.5 meters long) semi-aquatic forms. Others, more advanced, were small and resembled newts or salamanders (Limnerpeton), and one group, represented by the genus Branchiosaurus and its relatives, even retained external gills like the modern-day axolotl ("Mexican walking fish"). During the latest Carboniferous and early Permian, several groups evolved strong, robust limbs and vertebrae, and became adapted to life on land (Cacops) or as large (c. 1.5 meters long) and heavy-bodied semi-aquatic predators (Trematops, Eryops). Others developed long snouts and an astonishing similarity to crocodiles (e.g. Archegosaurus) although lacking armour. This last group included the largest known amphibian, the 9 meter long Prionosuchus of Brazil. Binomial name Ambystoma mexicanum (Shaw, 1789) The Axolotl (Ambystoma mexicanum) is an aquatic salamander native to Mexico. ... The Late Pennsylvanian (also known as the Upper Pennsylvanian) is the third and final of three subepochs of the Pennsylvanian epoch of the Carboniferous period. ... Cisuralian is the first of the three epoches of the Permian. ... Cacops was a genus of Dissorophid amphibians that is known from the Early Permian of Texas. ... 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...

During the later Permian, increasing aridity and more successful reptiles meant the end of the terrestrial forms, but semi- and fully-aquatic animals continued to flourish, including the large archegosaur Melosaurus of Eastern Europe.

As these amphibians continued to flourish and diversify in the lakes and rivers of the late Permian, a number of groups became more dependent on life in the water. The vertebrae became weak, the limbs small and vestigal, and the heavy skull large and flat, with the eyes looking upwards. These include the classic Stereospondyli, along with other related types. During the Triassic period these animals dominated the fresh-water ecosystems, evolving in a range of both small and large forms. During the Early Triassic one group of successful long-snouted fish eaters, the Trematosaurs, even adapted to a life in the sea, the only amphibians to do so. The Capitosauroidea included not only medium-sized but also many giant species, 2.3 to 4 meters or more in length (e.g. Paracyclotosaurus, Cyclotosaurus), with huge and extraordinarily flat skulls, over a meter long in the largest forms (Mastodonsaurus). These animals seem to have lived on the river bottom, perhaps spending most or all their entire lives in water, and catching their prey by a sudden opening of the upper jaw, sucking in any unwary fish or smaller tetrapod that happened to be swimming past. In the late Triassic (Carnian) these big amphibains were joined by the superficially very similar Metoposauridae (1.5 meters long - and distingusihed mainly by the different posiition of the eye-sockets), and the curious wide-headed Plagiosaurs (about a meter in length), with external gills. Lopingian is the third of the three epoches of the Permian. ... The Triassic is a geologic period that extends from about 245 to 202 Ma (million years ago). ... Scythia was an area in Eurasia inhabited in ancient times by an Indo-Aryans known as the Scythians. ... The Late Triassic (also known as Upper Triassic, or Keuper) is the third and final of three epochs of the Triassic period. ... The Carnian is a stage on the geologic time scale occuring from 228 +/- 2 to 216. ... 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. ...

The Triassic-Jurassic extinction event killed all the giant temnospondyls. Only the two Gondwanan families survived; the Brachyopidae and Chigutosauridae. Interestingly these grew to large size during the Jurassic, with the Brachyopids flourishing in China, and the Chigutosaurs in Gondwana. The Triassic-Jurassic extinction event is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans. ... Pangea broke into the two supercontinents, Laurasia and Gondwana The southern supercontinent Gondwana (originally Gondwanaland) included most of the landmasses which make up todays continents of the southern hemisphere, including Antarctica, South America, Africa, Madagascar, India, Arabia, Australia-New Guinea and New Zealand. ...

The most recent known temnospondyl was the giant Chigutosaur, Koolasuchus, known from the middle Cretaceous of Australia (where it seems to have survived in rift valleys that were free of crocodiles, co-existing with dinosaurs). At up to 5 meters in length, this was one of the largest of its kind, as well as the last. Koolasuchus was a large Cretaceous amphibian that lived on the continent of Australia. ... 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. ... In geology, a rift valley is a valley created by the formation of a rift. ... Subfamilies Family Crocodylidae    Crocodylinae    Alligatorinae    Gavialinae Crocodylia (or crocodylians) is an order of large reptiles that scientists believe branched off from class Reptilia about 220 million years ago. ...

References

• Benton, M. J. (2000), Vertebrate Paleontology, 2nd Ed. Blackwell Science Ltd 3rd ed. (2004) - see also taxonomic hierarchy of the vertebrates, according to Benton 2004
• 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.)
• Laurin, M. (1996) Terrestrial Vertebrates - Stegocephalians: Tetrapods and other digit-bearing vertebrates, Tree of Life project
• Laurin, M. and Steyer, J-S (2000) Phylogeny and Apomorphies of Temnospondyls, Tree of Life project
• Reisz, Robert, (no date), Biology 356 - Major Features of Vertebrate Evolution - The Origin of Tetrapods and Temnospondyls
• Steyer, J-S and Laurin, M. (2000) Temnospondyli, Tree of Life project
• Yates, A. M. & Warren, A. A. (2000), The phylogeny of the 'higher' temnospondyls (Vertebrata: Choanata) and its implications for the monophyly and origins of the Stereospondyli. Zool. J. Linnean Soc. 128: 77-121.

Robert L. Carroll (b. ... Edwin H. Colbert (1905 – 2001) was a distinguished vertebrate paleontologist and prolific researcher and author. ...

External links

• Temnospondyli - Tree of Life project
• Temnospondyli - Palaeos
• Temnospondyli - Permian Tetrapods