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Temnospondyli (from
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse
order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of ...
of small to giant
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—often considered primitive amphibians—that flourished worldwide during the
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 ''Carboniferou ...
,
Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...
, and
Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...
periods. A few species continued into the
Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
and
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
periods. Fossils have been found on every continent. During about 210 million years of evolutionary history, they adapted to a wide range of habitats, including freshwater, terrestrial, and even coastal marine environments. Their life history is well understood, with fossils known from the
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
l stage,
metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
, and maturity. Most temnospondyls were
semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...
, although some were almost fully terrestrial, returning to the water only to breed. These temnospondyls were some of the first vertebrates fully adapted to life on land. Although temnospondyls are considered amphibians, many had characteristics, such as scales and armour-like bony plates, that distinguish them from modern amphibians (
lissamphibia The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relativ ...
ns). Temnospondyls have been known since the early 19th century, and were initially thought to be
reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates ( lizards and snakes) and rhynchocephalia ...
s. They were described at various times as
batrachia The Batrachia are a clade of amphibians that includes frogs and salamanders, but not caecilians nor the extinct allocaudates. The name Batrachia was first used by French zoologist Pierre André Latreille in 1800 to refer to frogs, but has more ...
ns,
stegocephalia Stegocephali (often spelled Stegocephalia) is a group containing all four-limbed vertebrates. It is equivalent to a broad definition of Tetrapoda: under this broad definition, the term "tetrapod" applies to any animal descended from the first ve ...
ns, and labyrinthodonts, although these names are now rarely used. Animals now grouped in Temnospondyli were spread out among several amphibian groups until the early 20th century, when they were found to belong to a distinct
taxon In biology, a taxon ( back-formation from '' taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular n ...
based on the structure of their vertebrae. Temnospondyli means "cut vertebrae", as each vertebra is divided into several parts (intercentrum, paired pleurocentra, neural arch), although this occurs widely among other early tetrapods. Experts disagree over whether temnospondyls were ancestral to modern amphibians (
frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...
s,
salamander Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All t ...
s, and
caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...
s), or whether the whole group died out without leaving any descendants. Different hypotheses have placed modern amphibians as the descendants of temnospondyls, as descendants of another group of early tetrapods called lepospondyls, or even as descendants of both groups (with caecilians evolving from lepospondyls and frogs and salamanders evolving from temnospondyls). There is further disagreement about a temnospondyl origin of lissamphibians related to whether the modern groups arose from only one group (
dissorophoids Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
) or from two different groups (dissorophoids and stereospondyls). The majority of studies place a group of temnospondyls called amphibamiforms as the closest relatives of modern amphibians. Similarities in teeth, skulls, and hearing structures link the two groups.


Description

Many temnospondyls are much larger than living amphibians, and superficially resemble
crocodile Crocodiles (family Crocodylidae) or true crocodiles are large semiaquatic reptiles that live throughout the tropics in Africa, Asia, the Americas and Australia. The term crocodile is sometimes used even more loosely to include all extant me ...
s, which has led many taxa to be named with the suffix -''suchus''. The largest taxa, which were predominantly the
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...
stereospondyls, had skulls exceeding one meter in length, and the entire animal would have been several meters in length (for reference, the largest living amphibian, ''
Andrias ''Andrias'' is a genus of giant salamanders. It includes the largest salamanders in the world, with ''A. japonicus'' reaching a length of , and ''A. sligoi'' reaching . While extant species are only known from East Asia, several extinct specie ...
'', is about 1.8 meters in body length). Others are smaller and resemble salamanders, in particularly the amphibamiform and micromelerpetid dissorophoids.


Cranium

Skulls are rounded or triangular in shape when viewed from above, and they were particularly flattened in semiaquatic to aquatic taxa, with dorsally facing orbits. The skull is usually covered in pits and ridges to form a honeycomb-like pattern. One of the most recent hypotheses for the function of the dermal ornamentation is that it may have supported blood vessels, which could transfer
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
to the bones to neutralize acidic build up in the blood (early semiaquatic tetrapods would have had difficulty expelling carbon dioxide from their bodies while on land, and these
dermal bone A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton including much of the skull, jaws, gill covers, shoulder girdle and fin spines rays ( le ...
s may have been an early solution to the problem). However, there are many other possible hypotheses for the purpose of the ornamentation (e.g., increasing surface area for better adhesion of the skin to the skull), and the function(s) remains largely unresolved due to the absence of this feature in lissamphibians. Some temnospondyls also exhibit raised tubercles or pustules instead of pits and grooves (e.g., the dissorophoid ''
Micropholis ''Micropholis'' is group of trees in the family Sapotaceae, described as a genus in 1891. (2001): World Checklist of Sapotaceae &ndash''Micropholis'' The Board of Trustees of the Royal Botanic Gardens, Kew. Retrieved 2008-DEC-24. These trees ar ...
'', plagiosaurine plagiosaurids), and the import of this disparity is also unclear. Many temnospondyls also have canal-like grooves in their skulls called sensory
sulci Sulci or Sulki (in Greek , Steph. B., Ptol.; , Strabo; , Paus.), was one of the most considerable cities of ancient Sardinia, situated in the southwest corner of the island, on a small island, now called Isola di Sant'Antioco, which is, how ...
, the presence of which is used to infer an aquatically inclined lifestyle. The sulci, which usually run around the nostrils and eye sockets, are part of a
lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelial ...
system used to detect vibrations in water in modern fish and certain modern amphibians. Many taxa, especially those inferred to have been terrestrial, have an opening at the midline near the tip of the snout called the internarial fenestra / fontanelle; this may have housed a mucus gland used in prey capture. In zatracheids, this opening is greatly enlarged for an unknown purpose. Homologues of most of the bones of temnospondyls are also seen in other early tetrapods, aside from a few bones in the skull, such as interfrontals, internasals, and
interparietal An interparietal bone (os interparietale or Inca bone or ''os inca var.'') is a dermal bone situated between the parietal and supraoccipital. It is homologous to the postparietal bones of other animals. In humans, it corresponds to the upper p ...
s, that have developed in some temnospondyl taxa. The intertemporal, a bone common in stem tetrapods, is only found in some late
Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ...
taxa like certain
edopoids Edopoidea is a clade of primitive temnospondyl amphibians including the genus ''Edops'' and the family Cochleosauridae. Edopoids are known from the Late Carboniferous and Early Permian of North America and Europe, and the Late Permian of Africa. ...
and
dvinosaurs Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from t ...
. Most temnospondyls have an indentation at the back of the skull called otic notches. It has typically been inferred that this structure supported a typanum for hearing, although there is substantial variation among temnospondyls in the anatomy of this notch such that it may not have served this function in all temnospondyls, and some clades like plagiosaurids and
brachyopids Brachyopidae is an extinct family of temnospondyl labyrintodonts. They evolved in the early Mesozoic and were mostly aquatic. A fragmentary find from Lesotho, Africa is estimated to have been long, the largest amphibian ever known to have lived ...
lack notches entirely. The palate of temnospondyls generally consists of the same bones found in other early tetrapods. Among the most distinguishing features of temnospondyls are the interpterygoid vacuities, two large holes in the back of the
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...
. Recent studies have suggested that these large openings provided additional attachment sites for musculature and that many temnospondyls were capable of retracting their eyeballs through the vacuities, which is observed in modern frogs and salamanders that also have these large palatal openings; there is no evidence for a buccal pump mechanism for respiration. Temnospondyls often have extensive coverings of teeth on their palates, as well as in their jaws, in contrast to modern amphibians. Some of these teeth are so large, they are referred to as tusks or fangs. Although most temnospondyls have monocuspid teeth, the presence of bicuspid and/or pedicellate teeth in some dissorophoids has been cited as evidence for close relatedness to lissamphibians. In some temnospondyls, such as the dvinosaur '' Erpetosaurus'', the
capitosaur Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts ...
'' Mastodonsaurus'', and the
trematosaur Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other (according to Yates and Warren 2000) being the Capitosauria. The trematosaurs were a diverse and important group t ...
''
Microposaurus ''Microposaurus'' (meaning "small eyed lizard"; from Greek , "small" + , "face" or "eye" + , "lizard") is an extinct genus of trematosaurid temnospondyl. Fossils are known from the Cynognathus Assemblage Zone of the Beaufort Group (part of the K ...
'', tusks in the lower jaw pierce the palate and emerge through openings in the top of the skull.


Postcranium

Temnospondyls'
vertebrae The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
are divided into several segments. In living tetrapods, the main body of the vertebra is a single piece of bone called the centrum, but in temnospondyls, this region was divided into a pleurocentrum and intercentrum. Two primary types of vertebrae are recognized in temnospondyls: stereospondylous and rhachitomous vertebrae. In rhachitomous vertebrae, the intercentra are large and wedge-shaped, and the pleurocentra are relatively small blocks that fit between them. Both elements support a spine-like neural arch, and well-developed interlocking projections called zygapophyses strengthen the connections between vertebrae. The strong backbone and strong limbs of many rhachitomous temnospondyls allowed them to be partially, and in some cases fully, terrestrial. In stereospondylous vertebrae, the pleurocentra have been greatly reduced or lost entirely, with the intercentra enlarged as the main body of the vertebrae. Early concepts of stereospondyl required the pleurocentra to be entirely absent, but newer concepts only require that the intercentrum has become greatly enlarged. This weaker type of backbone indicates that stereospondylous temnospondyls spent more time in water. Additional types that are less common are the plagiosaurid-type in which there is a single enlarged centrum of uncertain homology; and the tupilakosaurid-type vertebrae (diplospondyly) in which the pleurocentra and intercentra are the same size and form discs; this occurs in tupilakosaurid dvinosaurs but also at least some brachyopids and several other non-temnospondyls. The neural spines tend to be of similar height throughout the presacral region of the trunk, but some temnospondyls exhibit increasing height towards the mid-trunk, followed by a decrease in height to produce a more hump-backed contour. The most extreme is observed in the dissorophid ''
Platyhystrix ''Platyhystrix'' (from el, πλατύς , 'flat' and el, ῠ̔́στρῐξ , 'porcupine') was a temnospondyl amphibian with a distinctive sail along its back, similar to the unrelated synapsids, ''Dimetrodon'' and '' Edaphosaurus''. It lived d ...
'', which has greatly elongated neural spines that form a large sail on its back. The function of this sail, like that of the contemporaneous
sphenacodontids Sphenacodontidae (Greek: "wedge point tooth family") is an extinct family (biology), family of small to large, advanced, carnivore, carnivorous, Late Pennsylvanian to Guadalupian, middle Permian pelycosaurs. The most recent one, ''Dimetrodon ang ...
and edaphosaurids, remains enigmatic, but it is thought to have stiffened the vertebral column in association with the relative terrestriality of this clade. The majority of temnospondyls have presacral counts between 23 and 27, with reduction observed in some amphibamiforms and elongation observed in many dvinosaurs. Caudal length is highly variable, and complete caudal sequences are rare. Based on ''Eryops'', more than 30 caudal positions were possible in some taxa. The pectoral girdle comprised an unpaired interclavicle, paired clavicles, paired cleithra, and paired scapulocoracoids as with most other early tetrapods. These elements differ widely in variation across temnospondyls, with such variation attributed to different lifestyles. The interclavicle and clavicles tend to be more lightly built in terrestrial taxa, with little to no ornamentation. In contrast, these elements are massively ossified in the aquatic stereospondyls and are well-ornamented in the same fashion as the skull. The cleithrum and scapulocoracoid is more developed in terrestrial taxa, and the coracoid tends not to ossify in aquatic forms such that there is only a much shorter scapula present. The pelvis comprises the ilium, ischium, and pubis, the last of which does not always ossify in aquatic forms. The sutural contacts between elements may also be visible, even when all three ossify. The forelimb comprised the typical radius, ulna, humerus, and manus. These bones are typically more developed with greater surface area for muscle attachment in taxa inferred to have been terrestrial. Many dissorophoids have long and slender limbs. Historically it has been thought that all temnospondyls had only four fingers, but this has been shown not to be true in at least a few stereospondyls (''Metoposaurus'', '' Paracyclotosaurus''), and the paucity of complete manuses casts doubt on the sweeping characterization of a four-fingered manus as the predominant or plesiomorphic condition. At least in
Metoposauridae Metoposauridae is an extinct family of trematosaurian temnospondyls. The family is known from the Triassic period. Most members are large, approximately long and could reach 3 m long.Brusatte, S. L., Butler R. J., Mateus O., & Steyer S. J. (201 ...
, there are both taxa with four fingers and taxa with five. The hindlimb comprised the typical tibia, fibula, femur, and pes. Relative development is as with the forelimb. All temnospondyls with a known pes have five digits. Unlike modern amphibians, many temnospondyls are covered in small, closely packed scales. The undersides of most temnospondyls are covered in rows of large ventral plates. During early stages of development, they first have only small, rounded scales. Fossils show, as the animals grew, the scales on the undersides of their bodies developed into large, wide ventral plates. The plates overlap each other in a way that allows a wide range of flexibility. Later semiaquatic temnospondyls, such as
trematosaur Trematosauria is one of two major groups of temnospondyl amphibians that survived the Permian-Triassic extinction event, the other (according to Yates and Warren 2000) being the Capitosauria. The trematosaurs were a diverse and important group t ...
s and
capitosaur Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts ...
s, have no evidence of scales. They may have lost scales to make movement easier under water or to allow
cutaneous respiration Cutaneous respiration, or cutaneous gas exchange (sometimes called, skin breathing), is a form of respiration in which gas exchange occurs across the skin or outer integument of an organism rather than gills or lungs. Cutaneous respiration may be ...
, the absorption of oxygen through the skin. Several groups of temnospondyls have large bony plates (
osteoderm Osteoderms are bony deposits forming scales, plates, or other structures based in the dermis. Osteoderms are found in many groups of extant and extinct reptiles and amphibians, including lizards, crocodilians, frogs, temnospondyls (extinct amp ...
s) on their backs. One temnospondyl, ''
Peltobatrachus ''Peltobatrachus'' (from Greek ''pelte'', meaning shield and batrakhos, meaning frog) is an extinct genus of temnospondyl amphibian from the late Permian period of Tanzania. The sole species, ''Peltobatrachus pustulatus'', is also the sole membe ...
'', has armour-like plating that covers both its back and underside. The rhytidosteid '' Laidleria'' also has extensive plating on its back. Most members of the family
Dissorophidae Dissorophidae is an extinct family of medium-sized, temnospondyl amphibians that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America. History of study Dissorophidae is a ...
also have armor, although it only covers the midline of the back with one or two narrow rows of plates that tightly articulated with the vertebrae, and osteoderms are also known from a few trematopids. Other temnospondyls, such as ''
Eryops ''Eryops'' (; from Greek , , 'drawn-out' + , , 'face', because most of its skull was in front of its eyes) is a genus of extinct, amphibious temnospondyls. It contains the single species , the fossils of which are found mainly in early Permian (a ...
'', have been found with small, disc-like bony
scute A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...
s that were in life probably embedded in the skin. All of these temnospondyls were adapted to a terrestrial lifestyle. Armor may have offered protection from predators in the case of ''Peltobatrachus''. The scutes may have provided stability for the spine, as they would have limited flexibility and may have been connected by strong ligaments. A carapace of osteoderms is also seen in plagiosaurids, the only primarily aquatic clade with such extensive ossifications. Plagiosaurids may have inherited their armor from a terrestrial ancestor, as both ''Peltobatrachus'' and ''Laidleria'' have been considered close relatives of the group. Alternatively, these osteoderms may have served as mineral reservoirs to allow plagiosaurids to respond to a variety of environmental conditions. Contrary to older assumptions, more recent studies have argued that the temnospondyls evolved from a terrestrial ancestor (although with aquatic eggs and larvae), and that it was the forms that later returned to water and an aquatic lifestyle which evolved a spine more rigid and stiffer than the terrestrial species.


Soft tissue

Very little is known of the soft tissue of temnospondyls because the conditions necessary to preserve such material are uncommon. The most extensive records come from fine-grained deposits in the Carboniferous and Permian of Germany; the small-bodied and aquatic dissorophoids and the larger stereospondylomorphs are frequently preserved with outlines of soft tissue around the skeleton. Typically preserved features include the outline of the body, external gills, and parts of the eye or stomach. An amphibamiform specimen from the
Mazon Creek The Mazon Creek fossil beds are a conservation ' found near Morris, in Grundy County, Illinois. The fossils are preserved in ironstone concretions, formed approximately in the mid- Pennsylvanian epoch of the Carboniferous period. These concretio ...
locality was described as having toepad-like features. Trace fossils attributed to temnospondyls are fairly common, especially from the Carboniferous through the Triassic. Common ichnogenera include '' Batrachichnus'' and ''
Limnopus ''Limnopus'' is an ichnogenus of ancient tetrapod footprint. Its footprints have been found in Moscovian aged-rocks situated in Alverley, Shropshire, England, Colorado and West Virginia. The ''Limnopus'' tracks were probably made by ''Diadecte ...
''.


History of study

Temnospondyli was named by the German palaeontologist
Karl Alfred von Zittel Karl Alfred Ritter von Zittel (25 September 1839 – 5 January 1904) was a German palaeontologist best known for his ''Handbuch der Palaeontologie'' (1876–1880). Biography Karl Alfred von Zittel was born in Bahlingen in the Grand Duchy o ...
in his second edition of ''Handbuch der Palaeontologie'', published in 1888. However, temnospondyl remains have been known since the early part of the 19th century. The earliest described temnospondyl was '' Mastodonsaurus'', named by Georg Friedrich Jaeger in 1828 from a single tooth that he considered to belong to a reptile. ''Mastodonsaurus'' means "breast tooth lizard" after the nipple-like shape of the tip of the tooth. The naming of these first specimens was disputed.
Leopold Fitzinger Leopold Joseph Franz Johann Fitzinger (13 April 1802 – 20 September 1884) was an Austrian zoologist. Fitzinger was born in Vienna and studied botany at the University of Vienna under Nikolaus Joseph von Jacquin. He worked at the Vienna Natur ...
named the animal ''
Batrachosaurus ''Batrachosaurus'' is an extinct genus of prehistoric brachyopoid amphibian that lived in Germany during the Middle Triassic (Ladinian). The genus was named by Joseph Fitzinger in 1837 and the type species, ''B. jaegeri'', was named three year ...
'' in 1837. In 1841, the English palaeontologist
Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Ow ...
referred to the genus as ''Labyrinthodon'' to describe its highly folded or labyrinthine teeth. Owen thought that the name ''Mastodonsaurus'' "ought not to be retained, because it recalls unavoidably the idea of the mammalian genus ''Mastodon'', or else a mammilloid form of the tooth... and because the second element of the word, ''saurus'', indicates a false affinity, the remains belonging, not to the Saurian, but to the Batrachian order of Reptiles." Owen recognized that the animal was not a " saurian" reptile, yet he also referred Jaeger's '' Phytosaurus'' to the genus. Although the two genera have similarly sized conical teeth, ''Phytosaurus'' was later found to be a crocodile-like reptile. Additional material, including skulls, firmly placed ''Labyrinthodon'' as an amphibian. Jaeger also named ''Salamandroides giganteus'' in 1828, basing it on partial occiput, or back portion of the skull. In 1833, he described a complete skull of ''S. giganteus'' that had the same teeth as his ''Mastodonsaurus'', making it the first known complete skull of a temnospondyl. Because ''Mastodonsaurus'' was named first, it has precedence over the other names as a senior subjective synonym. ''Batrachosaurus'' is still used as the name of an unrelated
brachyopid Brachyopidae is an extinct family of temnospondyl labyrintodonts. They evolved in the early Mesozoic and were mostly aquatic. A fragmentary find from Lesotho, Africa is estimated to have been long, the largest amphibian ever known to have li ...
temnospondyl. ''Mastodonsaurus'' and other similar animals were referred to as
labyrinthodont "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 conside ...
s, named like ''Labyrinthodon'' for teeth that were highly folded in cross section. Owen's "''Labyrinthodon Jaegeri''" was later found at
Guy's Cliffe Guy's Cliffe (variously spelled with and without an apostrophe and a final "e") is a hamlet and former civil parish on the River Avon and the Coventry Road between Warwick and Leek Wootton, in the parish of Leek Wootton and Guy's Cliffe, in the ...
,
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 ...
by paleontologist
William Buckland William Buckland DD, FRS (12 March 1784 – 14 August 1856) was an English theologian who became Dean of Westminster. He was also a geologist and palaeontologist. Buckland wrote the first full account of a fossil dinosaur, which he named ' ...
. Other specimens were found in the red sandstone of
Warwickshire Warwickshire (; abbreviated Warks) is a county in the West Midlands region of England. The county town is Warwick, and the largest town is Nuneaton. The county is famous for being the birthplace of William Shakespeare at Stratford-upon-Avo ...
. As more fossils were uncovered in England, Owen depicted these labyrinthodonts as the "highest" form of batrachian and compared them to crocodiles, which he considered the highest form of reptiles. He also noted the large labyrinthodonts of the
Keuper The Keuper is a lithostratigraphic unit (a sequence of rock strata) in the subsurface of large parts of west and central Europe. The Keuper consists of dolomite, shales or claystones and evaporites that were deposited during the Middle and Lat ...
(a unit of rocks that dates to the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...
) were younger than more advanced reptiles in the Magnesian and
Zechstein The Zechstein (German either from ''mine stone'' or ''tough stone'') is a unit of sedimentary rock layers of Middle to Late Permian (Guadalupian to Lopingian) age located in the European Permian Basin which stretches from the east coast of Englan ...
, which are
Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
in age. Owen used these fossils to counter the notion that reptiles evolved from a sequential progression from early amphibians (what he called "metamorphosed fishes"). In addition to ''Mastodonsaurus'', some of the earliest named genera included '' Metopias'' and '' Rhombopholis'' in 1842, ''
Zygosaurus ''Zygosaurus'' is an extinct genus of dissorophid temnospondyl from the Middle-Late Permian of Russia. It was described in 1848 by Eduard Eichwald, making it the first dissorophid to be described and is known from a single species, ''Zygosaurus ...
'' in 1848, ''
Trematosaurus ''Trematosaurus'' is an extinct genus of trematosaurid temnospondyl amphibian found in Germany and Russia. It was first named by Hermann Burmeister in 1849 and the type species is ''Trematosaurus brauni''. History of study ''Trematosaurus' ...
'' in 1849, ''
Baphetes ''Baphetes'' is an extinct genus of tetrapod from the Pennine Coal Measures Group and Parrot Coal, England, the Joggins Formation of Nova Scotia, and the Kladno Formation of the Czech Republic. It was first named by Richard Owen in 1854. The ...
'' and ''
Dendrerpeton ''Dendrerpeton'' (from el, δένδρον , 'tree' and el, ἑρπετόν , 'creeping thing') is a genus of an extinct group of temnospondyl amphibians. Its fossils have been found primarily in the Joggins Formation of Eastern Canada and in I ...
'' in 1853, '' Capitosaurus'' in 1858, and '' Dasyceps'' in 1859. ''Baphetes'' is now placed as an early tetrapod outside Temnospondyli, and ''Rhombopholis'' is now considered a
prolacertiform Protorosauria is an extinct polyphyletic group of archosauromorph reptiles from the latest Middle Permian (Capitanian stage) to the end of the Late Triassic ( Rhaetian stage) of Asia, Europe and North America. It was named by the English an ...
reptile. Later in the 19th century, temnospondyls were classified as various members of
Stegocephalia Stegocephali (often spelled Stegocephalia) is a group containing all four-limbed vertebrates. It is equivalent to a broad definition of Tetrapoda: under this broad definition, the term "tetrapod" applies to any animal descended from the first ve ...
, a name coined by the American paleontologist
Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interes ...
in 1868. Cope placed stegocephalians in the class Batrachia, the name then used for
Amphibia Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...
. Stegocephalia means "roof-headed" in
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
, a reference to the wide, flat heads of temnospondyls and other early tetrapods. During this time, palaeontologists considered temnospondyls to be amphibians because they possessed three main features:
gill arch Branchial arches, or gill arches, are a series of bony "loops" present in fish, which support the gills. As gills are the primitive condition of vertebrates, all vertebrate embryos develop pharyngeal arches, though the eventual fate of these arc ...
es in juvenile skeletons, indicating they were amphibious for at least the first part of their lives; ribs that do not connect at the underside of the rib cage; and deep pits in the skull that were interpreted as space for mucous glands. Several suborders of stegocephalians were recognized in the late 19th and early 20th centuries. Animals now regarded as temnospondyls were primarily labyrinthodonts, but some were classified in the Branchiosauria. Branchiosaurs were small-bodied and had simple conical teeth, while labyrinthodonts were larger and had complex, folded
dentin Dentin () (American English) or dentine ( or ) (British English) ( la, substantia eburnea) is a calcified tissue of the body and, along with enamel, cementum, and pulp, is one of the four major components of teeth. It is usually covered by e ...
and enamel in their teeth. Branchiosauria included only a few forms, such as ''
Branchiosaurus ''Branchiosaurus'' (from el, βράγχιον , 'gill' and el, σαῦρος , 'lizard') is a genus of small, lightly built early prehistoric amphibians. Fossils have been discovered in strata dating from the late Pennsylvanian Epoch to the ...
'' from Europe and ''
Amphibamus ''Amphibamus'' is a genus of amphibamid temnospondyl amphibians from the Carboniferous (middle Pennsylvanian) of North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisp ...
'' from North America, that had poorly developed bones, external gills, and no ribs. Some skeletons of ''Amphibamus'' were later found with long ribs, prompting its reassignment to
Microsauria Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considered ...
(although more detailed studies found it to be a temnospondyl). Soft tissue, such as scales and external gills, were found in many well-preserved branchiosaur fossils from Germany. In the early 20th century, branchiosaurs would be recognized as
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
l forms of temnospondyls lacking many of the typical features that define the group, and is no longer recognized as a distinct group. Other animals that would later be classified as temnospondyls were placed in a group called Ganocephala, which was characterized by plate-like skull bones, small limbs, fish-like scales, and branchial arches. Unlike labyrinthodonts, they did not have
parietal foramina A parietal foramen is an opening in the skull for the parietal emissary vein, which drains into the superior sagittal sinus. Occasionally, a small branch of the occipital artery can also pass through it. It is located at the back part of the par ...
, small holes in their skulls behind their eye sockets. '' Archegosaurus'', ''
Dendrerpeton ''Dendrerpeton'' (from el, δένδρον , 'tree' and el, ἑρπετόν , 'creeping thing') is a genus of an extinct group of temnospondyl amphibians. Its fossils have been found primarily in the Joggins Formation of Eastern Canada and in I ...
'', ''
Eryops ''Eryops'' (; from Greek , , 'drawn-out' + , , 'face', because most of its skull was in front of its eyes) is a genus of extinct, amphibious temnospondyls. It contains the single species , the fossils of which are found mainly in early Permian (a ...
'' and '' Trimerorhachis'' were placed in this group and were considered to be the most primitive members of Reptilia. Their rhachitomous vertebrae,
notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consi ...
, and lack of
occipital condyle The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra. The condyles are oval or reniform (kidney-shaped) in shape, and their anteri ...
s (which attached the head to the neck) were features that were also shared with fishes. Thus, they were considered a link between early fishes and more advanced forms such as stegocephalians. Another group was called
Microsauria Microsauria ("small lizards") is an extinct, possibly polyphyletic order of tetrapods from the late Carboniferous and early Permian periods. It is the most diverse and species-rich group of lepospondyls. Recently, Microsauria has been considered ...
by Cope in 1868. He classified Microsauria as a subgroup of Labyrinthodontia, placing many small, amphibian-like animals within it. Among them was ''Dendrerpeton'', once placed in Ganocephala. ''Dendrerpeton'' was later placed as a labyrinthodont with other temnospondyls, but confusion existed for many years over the classification of small amphibians. By the end of the 19th century, most of what are today regarded as temnospondyls were placed in the suborder Labyrinthodonta. The American paleontologist Ermine Cowles Case called it Labyrinthodonta ''vera'' or "true labyrinthodonts". The names Stegocephalia and Labyrinthodontia were used interchangeably to refer to the order in which it belonged. The labyrinthodontian suborders Microsauria and Branchiosauria, both of which contain temnospondyls, were distinct from Labyrinthodonta. Within Labyrinthodonta were the groups Rhachitomi, Labyrinthodonti, and Embolerimi. Members of Rhachitomi, such as ''Archegosaurus'' and ''Eryops'', had rhachitomous vertebrae with enlarged intercentra that displaced the pleurocentra. Labyrinthodonti, such as ''Mastodonsaurus'', ''Trematosaurus'', and ''
Micropholis ''Micropholis'' is group of trees in the family Sapotaceae, described as a genus in 1891. (2001): World Checklist of Sapotaceae &ndash''Micropholis'' The Board of Trustees of the Royal Botanic Gardens, Kew. Retrieved 2008-DEC-24. These trees ar ...
'', had lost their pleurocentra, and the intercentra made up the entire body of the vertebrae. Embolerimi had intercentra and pleurocentra that were of equal size. Embolomeres are now identified as
reptiliomorph Reptiliomorpha (meaning reptile-shaped; in PhyloCode known as ''Pan-Amniota'') is a clade containing the amniotes and those tetrapods that share a more recent common ancestor with amniotes than with living amphibians (lissamphibians). It was defi ...
s distantly related to temnospondyls. In 1888, von Zittel divided stegocephalians among three taxa: Lepospondyli, Temnospondyli, and
Stereospondyli The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecologi ...
. He placed microsaurs in Lepospondyli, a group which he characterized as having simple, spool-shaped vertebral centra. Temnospondyli included forms with the centra divided into pleurocentra and intercentra. All members of Stereospondyli had amphicoelous centra composed only of the intercentra. Cope objected to von Zittel's classification, considering the vertebrae of lepospondyls and stereospondyls indistinguishable because each had a simple spool shape. He continued to use Ganocephala and Labyrinthodonta (which he alternatively referred to as Rhachitomi) to distinguish animals based on the absence or presence of occipital condyles. Temnospondyli became a commonly used name at the turn of the 20th century. Paleontologists included both embolomeres and rhachitomes in the group. Cope's Ganocephala and Labyrinthodonta fell out of use. In 1919, British paleontologist
D. M. S. Watson Prof David Meredith Seares Watson FRS FGS HFRSE LLD (18 June 1886 – 23 July 1973) was the Jodrell Professor of Zoology and Comparative Anatomy at University College, London from 1921 to 1951. Biography Early life Watson was born in the High ...
proposed that the evolutionary history of these large amphibians could be seen through changes in their vertebrae. Embolomerous forms in the Carboniferous graded into rhachitomous forms in the Permian, and finally into stereospondyls in the Triassic. More importantly, Watson began using the term Labyrinthodontia to refer to these groups. The name Temnospondyli was rarely used in the decades that followed. Swedish paleontologist Gunnar Säve-Söderbergh removed embolomeres from the group, narrowing its scope to rhachitomes and stereospondyls. His classification of labyrinthodonts was based heavily on characteristics of the skull rather than the vertebrae. The American paleontologist
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 ...
brought the name Temnospondyli back into use in the later 20th century. Säve-Söderbergh used the name Labyrinthodontia in a strict sense (''
sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
'') to refer to Rhachitomi and Stereospondyli, excluding Embolomeri. Romer agreed with this classification, but used the name Temnospondyli to avoid confusion with Labyrinthodontia in its wider sense (''
sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...
''). Unlike modern temnospondyl classification, however, Romer included the primitive Ichthyostegalia in the group.


Evolutionary history


Carboniferous and Early Permian

Temnospondyls first appeared in the Early Carboniferous around 330 million years ago (Mya) where the earliest appearances are ''
Balanerpeton ''Balanerpeton'' is an extinct genus of temnospondyl amphibian from the Visean stage of the Early Carboniferous period. It is estimated to reach up to in length. ''Balanerpeton woodi'' was discovered by Stanley Wood and is the earliest and most ...
'' from Scotland and an indeterminate temnospondyl from Germany. During the Carboniferous, all of the rhachitome clades appeared, including dendrerpetids,
edopoids Edopoidea is a clade of primitive temnospondyl amphibians including the genus ''Edops'' and the family Cochleosauridae. Edopoids are known from the Late Carboniferous and Early Permian of North America and Europe, and the Late Permian of Africa. ...
, eryopoids, the various dissorophoid subclades, dvinosaurs, and zatracheids. Stereospondylomorphs and stereospondyls first appeared in the early Permian, although the former may have appeared earlier and merely be undocumented at present. The vast majority of the Carboniferous records come from the midwestern United States, like the Linton, Five Points, and Mazon Creek
lagerstätte A Lagerstätte (, from '' Lager'' 'storage, lair' '' Stätte'' 'place'; plural ''Lagerstätten'') is a sedimentary deposit that exhibits extraordinary fossils with exceptional preservation—sometimes including preserved soft tissues. These f ...
, and the south-central United States where classic redbed formations are found; and from western Europe, particularly the Saar-Nahe Basin in Germany and
Nýřany Nýřany (; german: Nürschan) is a town in Plzeň-North District in the Plzeň Region of the Czech Republic. It has about 6,900 inhabitants. Administrative parts Villages of Doubrava and Kamenný Újezd are administrative parts of Nýřany. Ge ...
in the Czech Republic. The early Permian record of temnospondyls is also concentrated in these regions. Most of the clades from the Late Carboniferous continued to be successful, with a particularly high diversity of dissorophoids.


Middle Permian

Whether there are any middle Permian records of temnospondyls is debated as a result of the uncertain age and correlation of different deposits in North America and Russia and the controversy over Olson's Gap.


Late Permian

During the
Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
, increasing aridity and the diversification of reptiles contributed to a decline in terrestrial temnospondyls, but semiaquatic and fully aquatic temnospondyls continued to flourish, including the large ''
Melosaurus ''Melosaurus'' is an extinct genus of temnospondyl amphibian. Fossils of it have been found in Russia. Fossil remains of ''Melosaurus uralensis'' were discovered at Belebei in Russia. Its fossils dated of the Asselian-Olenekian stages (299–24 ...
'' of Eastern Europe. Other temnospondyls, such as archegosaurids, developed long snouts and a close similarity to crocodiles, although they lacked the armor characteristic of the latter group. These temnospondyls included the largest known batrachomorph, the 9-m-long ''
Prionosuchus ''Prionosuchus'' is an extinct genus of large temnospondyl. A single species ''P. plummeri'', is recognized from the Early Permian (some time between 299 and 272 million years ago). Its fossils have been found in what is now northeastern Brazil. ...
'' of Brazil. The stereospondyl record is almost exclusively confined to rhinesuchids.


Mesozoic

As temnospondyls continued to flourish and diversify in the
Late Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
(260.4 - 251.0 Mya), a major group called Stereospondyli became more dependent on life in the water. The vertebrae became weak, the limbs small, and the skull large and flat, with the eyes facing upwards. During the Triassic period, these animals dominated the freshwater ecosystems, evolving in a range of both small and large forms. During the
Early Triassic The Early Triassic is the first of three epochs of the Triassic Period of the geologic timescale. It spans the time between Ma and Ma (million years ago). Rocks from this epoch are collectively known as the Lower Triassic Series, which is ...
(251.0 - 245.0 Mya) one group of successful long-snouted fish-eaters, the
trematosauroids Trematosauroidea are an important group of Triassic temnospondyl amphibians. They flourished briefly during the Early Triassic, occurring worldwide before declining at the start of the Middle Triassic, although the group continued until the Late ...
, even adapted to a life in the sea, the only known batrachomorphs to do so with the exception of the modern
crab-eating frog The crab-eating frog (''Fejervarya cancrivora'') is a frog native to south-eastern Asia including Taiwan, China, the Philippines and more rarely as far west as Orissa in India. It has also been introduced to Guam, and was most likely introduced f ...
. Another group, the capitosauroids, included medium- and large-sized animals in length, with large and flat skulls that could be over a meter long in the largest forms such as ''Mastodonsaurus''. These animals spent most or all their lives in water as aquatic predators, catching their prey by a sudden opening of the upper jaw and sucking in fish or other small animals. In the
Carnian The Carnian (less commonly, Karnian) is the lowermost stage (stratigraphy), stage of the Upper Triassic series (stratigraphy), Series (or earliest age (geology), age of the Late Triassic Epoch (reference date), Epoch). It lasted from 237 to 227 m ...
stage of the
Late Triassic The Late Triassic is the third and final epoch of the Triassic Period in the geologic time scale, spanning the time between Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch and followed by the Early Jurassic Epoch ...
(237.0 - 227.0 Mya), capitosauroids were joined by the superficially very similar
Metoposauridae Metoposauridae is an extinct family of trematosaurian temnospondyls. The family is known from the Triassic period. Most members are large, approximately long and could reach 3 m long.Brusatte, S. L., Butler R. J., Mateus O., & Steyer S. J. (201 ...
. Metoposaurids are distinguished from capitosauroids by the positioning of their eye sockets near the front of their skulls. Another group of stereospondyls, the plagiosaurs, had wide heads and
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...
s, and adapted to life at the bottom of lakes and rivers. By this time, temnospondyls had become a common and widespread component of semiaquatic ecosystems. Some temnospondyls, such as '' Cryobatrachus'' and ''
Kryostega ''Kryostega'' is a large temnospondyl amphibian from the Early or Middle Triassic of Antarctica. The genus is based on a single specimen collected in 1986 by a team led by paleontologist William H. Hammer of Augustana College, and now housed in ...
'', even inhabited
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...
, which was covered in temperate forests at the time. Triassic temnospondyls were often the dominant semiaquatic animals in their environments. Large assemblages of metoposaurs with hundreds of individuals preserved together have been found in the southwestern United States. They have often been interpreted as mass death events caused by droughts in floodplain environments. Recent studies show these dense assemblages were instead probably the result of currents accumulating dead individuals in certain areas. These environments seem to have had little diversity, as they were inhabited almost exclusively by
metoposaurs Metoposauridae is an extinct family of trematosaurian temnospondyls. The family is known from the Triassic period. Most members are large, approximately long and could reach 3 m long.Brusatte, S. L., Butler R. J., Mateus O., & Steyer S. J. (20 ...
. Temnospondyls reached a peak diversity during the Early Triassic, and progressively declined throughout the subsequent Middle and Late Triassic, with only 4 members of the Brachyopoidea surviving into the Jurassic and the Cretaceous. Among brachyopoids, the
brachyopids Brachyopidae is an extinct family of temnospondyl labyrintodonts. They evolved in the early Mesozoic and were mostly aquatic. A fragmentary find from Lesotho, Africa is estimated to have been long, the largest amphibian ever known to have lived ...
''
Gobiops ''Gobiops'' is an extinct genus of temnospondyl from the Jurassic of Mongolia, China, and possibly Kyrgyzstan. The genus is represented by a single species, ''Gobiops desertus''. It was named in 1991 from the Late Jurassic Shar Teeg Beds of Mong ...
'' and ''
Sinobrachyops ''Sinobrachyops placenticephalus'' is an extinct temnospondyl amphibian from Middle Jurassic-aged Shaximiao Formation in the Sichuan basin, China. ''S. placenticephalus'' is one of the youngest known labyrinthodont amphibians.Dong, Zhiming. ...
'' are known from Middle and
late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...
deposits across Asia and the
chigutisaurid Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. ...
''
Siderops ''Siderops'' is an extinct genus of chigutisaurid temnospondyl from Early Jurassic of Australia, containing the species ''S. kehli''. It is solely known from the holotype specimen, which consists of a nearly complete skull with mandible and pos ...
'' is known from the
Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
of Australia. The most recent known temnospondyl was the giant
chigutisaurid Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. ...
'' Koolasuchus'', known from the
Early Cretaceous The Early Cretaceous (geochronology, geochronological name) or the Lower Cretaceous (chronostratigraphy, chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145& ...
(
Aptian The Aptian is an age in the geologic timescale or a stage in the stratigraphic column. It is a subdivision of the Early or Lower Cretaceous Epoch or Series and encompasses the time from 121.4 ± 1.0 Ma to 113.0 ± 1.0 Ma (million years ag ...
) of
Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...
. It survived in
rift valley A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear d ...
s that were too cold in the winter for
Crocodylomorphs Crocodylomorpha is a group of pseudosuchian archosaurs that includes the crocodilians and their extinct relatives. They were the only members of Pseudosuchia to survive the end-Triassic extinction. During Mesozoic and early Cenozoic times, cr ...
that normally would have competed with them. ''Koolasuchus'' was one of the largest of the brachyopoids, with an estimated weight of .


Classification

Originally, temnospondyls were classified according to the structure of their vertebrae. Early forms, with complex vertebrae consisting of a number of separate elements, were placed in the suborder Rachitomi, and large Triassic aquatic forms with simpler vertebrae were placed in the suborder Stereospondyli. With the recent growth of
phylogenetics In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
, this classification is no longer viable. The basic rhachitomous condition is found in many primitive tetrapods, and is not unique to one group of temnospondyls. Moreover, the distinction between rhachitomous and stereospondylous vertebrae is not entirely clear. Some temnospondyls have rhachitomous, semirhachitomous, and sterospondylous vertebrae at different points in the same vertebral column. Other taxa have intermediate morphologies that do not fit into any category. Rachitomi is no longer recognized as a group, but Stereospondyli is still considered valid. Below is a simplified taxonomy of temnospondyls showing currently recognized groups: Class
Amphibia Amphibians are four-limbed and ectothermic vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arbo ...
*Order Temnospondyli **Superfamily Edopoidea ***Family
Cochleosauridae Cochleosauridae is a family of edopoid temnospondyl amphibians, among the most basal of temnospondyls. Most members of this family are known from the late Carboniferous ( Pennsylvanian) and early Permian (Cisuralian) of Europe and North America, ...
***Family Edopidae **Clade
Eutemnospondyli Eutemnospondyli (meaning "true Temnospondyli") is a clade of temnospondyl amphibians that includes most temnospondyls except edopoids. Eutemnospondyli was named by German paleontologist Rainer R. Schoch in 2013. He defined it as a stem-based ta ...
***Family Dendrerpetidae ***Clade Rhachitomi ****Suborder
Dvinosauria Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from t ...
*****Family Trimerorhachidae *****Superfamily Dvinosauroidea ******Family Dvinosauridae ******Family Eobrachyopidae ******Family
Tupilakosauridae Tupilakosauridae is an extinct family of dvinosaurian temnospondyls. It contains the genera ''Slaugenhopia'', '' Thabanchuia'', ''Tupilakosaurus'', and possibly ''Kourerpeton''. Tupilakosaurs are known from Texas, Greenland, Russia, and Fran ...
****Superfamily
Dissorophoidea Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
*****Family
Micromelerpetontidae Micromelerpetontidae (also spelled Micromelerpetidae) is an extinct family of dissorophoid temnospondyl amphibians that lived from the Late Carboniferous to the Early Permian in what is now Europe, with one Carboniferous species also known from ...
*****Clade
Xerodromes Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details o ...
******Clade
Amphibamiformes Amphibamiformes is an unranked clade with Dissorophoidea created by Schoch (2018). It encompasses all of the taxa traditionally considered to be "amphibamids" (subsequently restricted to '' Doleserpeton annectens'' and '' Amphibamus grandiceps'' ...
*******Family
Amphibamidae The Amphibamidae are an extinct family of dissorophoid temnospondyls known from Late Carboniferous-Early Permian strata in the United States. Classification Amphibamidae has traditionally included small-bodied, terrestrial dissorophoids. The ...
*******Family
Branchiosauridae Branchiosauridae is an extinct family of small amphibamiform temnospondyls with external gills and an overall juvenile appearance. The family has been characterized by hundreds of well-preserved specimens from the Permo-Carboniferous of Middle ...
********Subfamily
Branchiosaurinae Branchiosaurinae is an extinct subfamily of temnospondyl amphibians, part of the family Branchiosauridae Branchiosauridae is an extinct family of small amphibamiform temnospondyls with external gills and an overall juvenile appearance. The fa ...
*******Family Micropholidae *******Subclass
Lissamphibia The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relativ ...
? ( placement is uncertain) ******Clade
Olsoniformes Olsoniformes is a clade of dissorophoid temnospondyls. It includes the families Dissorophidae and Trematopidae. Most members of the clade were highly adapted to a terrestrial lifestyle. The clade was named in 2008 and is defined as the least inc ...
*******Family
Dissorophidae Dissorophidae is an extinct family of medium-sized, temnospondyl amphibians that flourished during the late Carboniferous and early Permian periods. The clade is known almost exclusively from North America. History of study Dissorophidae is a ...
********Subfamily
Dissorophinae Dissorophinae is a subfamily of dissorophid temnospondyls that includes '' Dissorophus'' and '' Broiliellus''. Phylogeny Below is the cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in ...
********Subfamily
Eucacopinae Eucacopinae is an extinct clade (evolutionary grouping) of dissorophid temnospondyls. Eucacopines differ from the other main group of dissorophids, the Dissorophinae, in having more lightly built skeletons and more knobby skulls. The subfamily ...
*******Family
Trematopidae Trematopidae is a family of dissorophoid temnospondyl spanning the late Carboniferous to the early Permian. Together with Dissorophidae, the family forms Olsoniformes, a clade comprising the medium-large terrestrial dissorophoids. Trematopids a ...
****Family Zatracheidae ****Clade
Eryopiformes Eryopiformes is a group of rhachitomi temnospondyl amphibians. Eryopiformes was named by the German paleontologist Rainer R. Schoch in 2013. He defined it as a node-based taxon to include Eryopidae and Stereospondylomorpha. Unlike previous ana ...
*****Suborder
Euskelia Euskelia is a clade of extinct Temnospondyl amphibians. ''Euskelia'' is a stem-based taxon including all temnospondyls more closely related to ''Eryops'' than to ''Parotosuchus ''Parotosuchus'' is an extinct genus of capitosaurian temnospondyl ...
******Superfamily
Dissorophoidea Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
? ******Superfamily
Eryopoidea Eryopoidea are a taxon of late Carboniferous and Permian temnospondyli amphibians, known from North America and Europe. Carroll includes no fewer than ten families, but Yates and Warren replace this with a cladistic approach and include three fa ...
*******Family Eryopidae *******Family Zatracheidae? *****Clade Limnarchia ******Suborder
Dvinosauria Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from t ...
? ******Clade
Stereospondylomorpha Stereospondylomorpha is a clade of temnospondyls. It includes the superfamily Archegosauroidea and the more diverse group Stereospondyli. Stereospondylomorpha was first proposed by Yates and Warren (2000), who found Archegosauroidea and Stereo ...
*******Superfamily
Archegosauroidea Archegosauroidea is an extinct superfamily of Permian temnospondyls. The superfamily is assigned to the clade Stereospondylomorpha and is the sister taxon to the suborder Stereospondyli. It includes the families Actinodontidae and Archegosaurid ...
********Family
Archegosauridae Archegosauridae is a family of relatively large and long snouted temnospondyls that lived in the Permian period. They were fully aquatic animals, and were metabolically and physiologically more similar to fish than modern amphibians.Florian Witzm ...
*********Subfamily
Melosaurinae Melosaurinae is an extinct subfamily of temnospondyl amphibians, part of the family Archegosauridae. Most melosaurines are known from Russia, although an unnamed species has been found in Brazil. Unlike the long-skulled archegosaurids of the fam ...
*********Subfamily Platyoposaurinae ********Family
Intasuchidae ''Intasuchus'' is an extinct genus of temnospondyl amphibian from the Middle Permian of Russia. It is known from a single species, ''Intasuchus silvicola'', which was named in 1956. ''Intasuchus'' belongs to the family Intasuchidae and is probabl ...
? ********Family Sclerocephalidae *******Suborder
Stereospondyli The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecologi ...
********Family
Peltobatrachidae ''Peltobatrachus'' (from Greek ''pelte'', meaning shield and batrakhos, meaning frog) is an extinct genus of temnospondyl amphibian from the late Permian period of Tanzania. The sole species, ''Peltobatrachus pustulatus'', is also the sole member ...
********Family
Lapillopsidae Lapillopsidae is a family of Temnospondyli. ''Lapillopsis'' was found as the sister to ''Rotaurisaurus'' in a 1999 analysis that found the Lapillopsidae as basal stereospondyls. ''Lapillopsis'' was found as a sister to Dissorophoidea by a 2017 ...
? ********Family Rhinesuchidae *********Clade
Superstes The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecolog ...
**********Family
Lydekkerinidae Lydekkerinidae is a family of stereospondyl temnospondyls that lived in the Early Triassic period. During this time period, lydekkerinids were widely distributed, with putative remains reported from Russia, Greenland, India, South Africa, Madagas ...
**********Clade
Neostereospondyli The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecolog ...
***********Clade
Capitosauria Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts ...
************Family Sclerothoracidae ************Superfamily Mastodonsauroidea *************Family
Heylerosauridae Heylerosauridae is a family of mastodonsauroid temnospondyls. It was first named in 1980 to include the genera '' Odenwaldia'' and '' Quasicyclotosaurus''. In addition to these genera, the family now includes '' Eocyclotosaurus'' and '' Yuanans ...
*************Family
Mastodonsauridae 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 Mastodonsauridae. Description S ...
*************Family
Stenotosauridae Stenotosauridae is an extinct family of mastodonsauroid temnospondyl Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often co ...
***********Clade Trematosauria ************Superfamily Trematosauroidea *************Family Thoosuchidae *************Family
Trematosauridae Trematosauridae are a family of large marine temnospondyl amphibians with many members. They first appeared during the Induan age of the Early Triassic, and existed until around the Carnian stage of the Late Triassic, although by then they wer ...
**************Subfamily Tertreminae **************Subfamily Lonchorhynchinae **************Subfamily Trematosaurinae ************Superfamily
Metoposauroidea Metoposauroidea is an extinct superfamily of temnospondyls that lived from the Middle to Upper Triassic in North America, Europe and North Africa. Metoposauroidea includes the families Metoposauridae Metoposauridae is an extinct family of ...
*************Order Gymnophionia? *************Family
Latiscopidae Latiscopidae is an extinct family of Mesozoic Era amphibian Temnospondyli Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often ...
*************Family
Metoposauridae Metoposauridae is an extinct family of trematosaurian temnospondyls. The family is known from the Triassic period. Most members are large, approximately long and could reach 3 m long.Brusatte, S. L., Butler R. J., Mateus O., & Steyer S. J. (201 ...
************Superfamily
Plagiosauroidea Plagiosauroidea is a superfamily of Temnospondyli that lived in the Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning o ...
*************Family Laidleriidae? *************Family
Plagiosauridae Plagiosauridae is a clade of temnospondyl amphibians of the Middle to Late Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the begi ...
************Superfamily
Rhytidosteoidea Rhytidosteoidea is a superfamily of Temnospondyli Temnospondyli (from Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order of small to giant tetrapods—often considered primitive a ...
*************Family Indobrachyopidae? *************Family Rhytidosteidae **************Subfamily Derwentiinae ************Clade
Brachyopomorpha Brachyopomorpha is a clade of stereospondyl temnospondyls within the infraorder Trematosauria. It was constructed in 2000 to include '' Bothriceps australis'' and the superfamily Brachyopoidea. It is phylogenetically defined as a stem-based ...
*************Superfamily Brachyopoidea **************Family
Brachyopidae Brachyopidae is an extinct family of temnospondyl labyrintodonts. They evolved in the early Mesozoic and were mostly aquatic. A fragmentary find from Lesotho, Africa is estimated to have been long, the largest amphibian ever known to have lived ...
**************Family
Chigutisauridae Chigutisauridae is an extinct family of large temnospondyl amphibians. The only genera recognized as belonging to Chigutisauridae at the current time are all from Gondwana. Chigutisaurids first appeared during the Early Triassic in Australia. Du ...


Phylogeny

In one of the earliest
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...
analyses of the group, Gardiner (1983) recognized five characteristics that made Temnospondyli a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
: a bone at the back of the skull, the
parasphenoid The parasphenoid is a bone which can be found in the cranium of many vertebrates. It is an unpaired dermal bone which lies at the midline of the roof of the mouth. In many reptiles (including birds), it fuses to the endochondral (cartilage-derived) ...
, is connected to another bone on the underside of the skull, the
pterygoid Pterygoid, from the Greek for 'winglike', may refer to: * Pterygoid bone, a bone of the palate of many vertebrates * Pterygoid processes of the sphenoid bone ** Lateral pterygoid plate ** Medial pterygoid plate * Lateral pterygoid muscle * Medi ...
; large openings called interpterygoid vacuities are present between the pterygoids; the
stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the foo ...
(a bone involved in hearing) is connected to the parasphenoid and projects upward; the
cleithrum The cleithrum (plural cleithra) is a membrane bone which first appears as part of the skeleton in primitive bony fish, where it runs vertically along the scapula. Its name is derived from Greek κλειθρον = "key (lock)", by analogy with "cla ...
, a bone in the
pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists of ...
, is thin; and part of the vertebra called the interdorsal attaches to the neural arch. Additional features were given by Godfrey ''et al.'' (1987), including the contact between the
postparietal Postparietals are cranial bones present in fish and many tetrapods. Although initially a pair of bones, many lineages possess postparietals which were fused into a single bone. The postparietals were dermal bones situated along the midline of the ...
and exoccipital at the back of the skull, small projections ( uncinate processes) on the
rib In vertebrate anatomy, ribs ( la, costae) are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the chest, enabling the lungs to expand and thus facilitate breathing by expanding the ches ...
s, and a
pelvic girdle The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The p ...
with each side having a single
iliac blade The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posteri ...
. These shared characteristics are called
synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ha ...
. Temnospondyls are placed as basal tetrapods in phylogenetic analyses, with their exact positioning varying between studies. Depending on the classification of modern amphibians, they are either included in the
crown group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor ...
Tetrapoda or the stem of Tetrapoda. Crown-group tetrapods are descendants of the most recent common ancestor of all living tetrapods and stem tetrapods are forms that are outside the crown group. Modern amphibians have recently been suggested as descendants of temnospondyls, which would place them within crown Tetrapoda. Below is a
cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...
from Ruta ''et al.'' (2003) placing Temnospondyli within crown Tetrapoda: Other studies place modern amphibians as the descendants of lepospondyls and place temnospondyls in a more basal position within the stem of Tetrapoda. Below is a cladogram from Laurin and Reisz (1999) placing Temnospondyli outside crown Tetrapoda: Most phylogenetic analyses of temnospondyl interrelationships focus on individual families. One of the first broad-scale studies of temnospondyl phylogeny was conducted by paleontologist Andrew Milner in 1990. A 2007 study made a "supertree" of all temnospondyl families, combining the family-level trees of previous studies. The following cladogram is modified from Ruta ''et al.'' (2007): 1 Temnospondyli, 2 Edopoidea, 3
Dvinosauria Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from t ...
, 4
Euskelia Euskelia is a clade of extinct Temnospondyl amphibians. ''Euskelia'' is a stem-based taxon including all temnospondyls more closely related to ''Eryops'' than to ''Parotosuchus ''Parotosuchus'' is an extinct genus of capitosaurian temnospondyl ...
, 5
Eryopoidea Eryopoidea are a taxon of late Carboniferous and Permian temnospondyli amphibians, known from North America and Europe. Carroll includes no fewer than ten families, but Yates and Warren replace this with a cladistic approach and include three fa ...
, 6
Dissorophoidea Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
, 7 Limnarchia, 8
Archegosauroidea Archegosauroidea is an extinct superfamily of Permian temnospondyls. The superfamily is assigned to the clade Stereospondylomorpha and is the sister taxon to the suborder Stereospondyli. It includes the families Actinodontidae and Archegosaurid ...
, 9
Stereospondyli The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecologi ...
, 10
Rhytidostea Rhytidostea is a clade of stereospondyl temnospondyls. It was erected in 2000 to include several temnospondyl groups distinct from the "higher" group of capitosaurs, including lydekkerinids, brachyopoids, and rhytidosteids. Rhytidosteans firs ...
, 11 Brachyopoidea, 12
Capitosauria Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts ...
, 13 Trematosauria, 14
Metoposauroidea Metoposauroidea is an extinct superfamily of temnospondyls that lived from the Middle to Upper Triassic in North America, Europe and North Africa. Metoposauroidea includes the families Metoposauridae Metoposauridae is an extinct family of ...
The most basal group of temnospondyls is the superfamily Edopoidea. Edopoids have several primitive or
plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...
features, including a single occipital condyle and a bone called the intertemporal that is absent in other temnospondyls. Edopoids include the Late Carboniferous genus ''
Edops ''Edops'' ('swollen face') is an extinct genus of temnospondyl amphibian from the Early Permian Period. Unlike more advanced temnospondyls of the time, such as ''Eryops'', ''Edops'' exhibited an archaic pattern of palatal bones, and still possess ...
'' and the family
Cochleosauridae Cochleosauridae is a family of edopoid temnospondyl amphibians, among the most basal of temnospondyls. Most members of this family are known from the late Carboniferous ( Pennsylvanian) and early Permian (Cisuralian) of Europe and North America, ...
.
Dendrerpetontidae Dendrerpetontidae is a family of Temnospondyli. Gallery Balanerpeton BW.jpg, '' Balanerpeton woodi'', of the early Carboniferous of Scotland Denderpeton DB.jpg, '' Dendrerpeton'', of the late Carboniferous of Nova Scotia and Ireland References ...
has also been included in Edopoidea, and is the oldest known temnospondyl family. '' Balanerpeton woodi'' is the oldest species, having been present over 330 million years ago during the
Viséan The Visean, Viséan or Visian is an age in the ICS geologic timescale or a stage in the stratigraphic column. It is the second stage of the Mississippian, the lower subsystem of the Carboniferous. The Visean lasted from to Ma. It follow ...
stage of the Early Carboniferous. Recent analyses place Dendrerpetontidae outside Edopoidea in a more derived position. Other primitive temnospondyls include '' Capetus'' and '' Iberospondylus''. '' Saharastega'' and '' Nigerpeton'', both described in 2005 from
Niger ) , official_languages = , languages_type = National languagesLate Permian Late may refer to: * LATE, an acronym which could stand for: ** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia ** Local-authority trading enterprise, a New Zealand business law ** Local average treatment effect, ...
. They are almost 40 million years younger than other basal temnospondyls, implying a long ghost lineage of species that are not yet known in the fossil record. In 2000, paleontologists Adam Yates and Anne Warren produced a revised phylogeny of more derived temnospondyls, naming several new clades. Two major clades were
Euskelia Euskelia is a clade of extinct Temnospondyl amphibians. ''Euskelia'' is a stem-based taxon including all temnospondyls more closely related to ''Eryops'' than to ''Parotosuchus ''Parotosuchus'' is an extinct genus of capitosaurian temnospondyl ...
and Limnarchia. Euskelia includes the temnospondyls that were once called rhachitomes and includes two subfamilies, the
Dissorophoidea Dissorophoideans are a clade of medium-sized, temnospondyl amphibians that appeared during the Moscovian in Euramerica, and continued through to the Late Permian and the Early Triassic of Gondwana. They are distinguished by various details of the ...
and the
Eryopoidea Eryopoidea are a taxon of late Carboniferous and Permian temnospondyli amphibians, known from North America and Europe. Carroll includes no fewer than ten families, but Yates and Warren replace this with a cladistic approach and include three fa ...
. Dissorophoids include small, mostly terrestrial temnospondyls that may be the ancestors of modern amphibians. Eryopoids include larger temnospondyls like ''Eryops''. The second major clade, Limnarchia, includes most Mesozoic temnospondyls, as well as some Permian groups. Within Limnarchia are the superfamily
Archegosauroidea Archegosauroidea is an extinct superfamily of Permian temnospondyls. The superfamily is assigned to the clade Stereospondylomorpha and is the sister taxon to the suborder Stereospondyli. It includes the families Actinodontidae and Archegosaurid ...
and the most derived temnospondyls, the stereospondyls. Yates and Warren also named
Dvinosauria Dvinosaurs are one of several new clades of Temnospondyl amphibians named in the phylogenetic review of the group by Yates and Warren 2000. They represent a group of primitive semi-aquatic to completely aquatic amphibians, and are known from t ...
, a clade of small aquatic temnospondyls from the Carboniferous, Permian, and Triassic. They placed Dvinosauria within Limnarchia, but more recent studies disagree on their position. For example, a 2007 study places them even more basal than euskelians, while a 2008 study keeps them as basal limnarchians. Within Stereospondyli, Yates and Warren erected two major clades:
Capitosauria Capitosauria is an extinct group of large temnospondyl amphibians with simplified stereospondyl vertebrae. Mainly living as piscivores in lakes and rivers, the Capitosauria and its sister taxon Trematosauria were the only major labyrinthodonts ...
and Trematosauria. Capitosaurs include large semiaquatic temnospondyls like ''Mastodonsaurus'' with flat heads and eyes near the back of the skull. Trematosaurs include a diversity of temnospondyls, including large marine trematosauroids, aquatic plagiosaurs, brachyopoids that survived into the Cretaceous, and metoposauroids with eyes near the front of their heads. In 2000, paleontologists Rainer Schoch and Andrew Milner named a third major clade of stereospondyls, the
Rhytidostea Rhytidostea is a clade of stereospondyl temnospondyls. It was erected in 2000 to include several temnospondyl groups distinct from the "higher" group of capitosaurs, including lydekkerinids, brachyopoids, and rhytidosteids. Rhytidosteans firs ...
. This group included more primitive stereospondyls that could not be placed in either Capitosauria or Trematosauria, and included groups like
Lydekkerinidae Lydekkerinidae is a family of stereospondyl temnospondyls that lived in the Early Triassic period. During this time period, lydekkerinids were widely distributed, with putative remains reported from Russia, Greenland, India, South Africa, Madagas ...
, Rhytidosteidae, and Brachyopoidea. While Capitosauria and Trematosauria are still widely used, Rhytidostea is not often supported as a true clade in recent analyses. Rhytidosteids and brachyopoids are now grouped with trematosaurians, but lydekkerinids are still considered to be a primitive family of stereospondyls. A new phylogeny of temnospondyls was offered by paleontologist Rainer Schoch in 2013. It supported many of the clades that were found by Yates and Warren, but it did not find support for their division of derived stereospondyls into Euskelia and Limnarchia. Eryopids were found to be more closely related to stereospondyls than to dissorophoids, which were grouped with dvinosaurs. The clade including Eryopidae and Stereospondylomorpha was named
Eryopiformes Eryopiformes is a group of rhachitomi temnospondyl amphibians. Eryopiformes was named by the German paleontologist Rainer R. Schoch in 2013. He defined it as a node-based taxon to include Eryopidae and Stereospondylomorpha. Unlike previous ana ...
. In addition, Schoch named the clade containing all temnospondyls except edopoids
Eutemnospondyli Eutemnospondyli (meaning "true Temnospondyli") is a clade of temnospondyl amphibians that includes most temnospondyls except edopoids. Eutemnospondyli was named by German paleontologist Rainer R. Schoch in 2013. He defined it as a stem-based ta ...
and reinstated the name Rhachitomi for the clade containing all temnospondyls except edopoids and dendrerpetontids. Below is the cladogram from Schoch's analysis:


Relationship to modern amphibians

Modern amphibians (frogs, salamanders, and caecilians) are classified in
Lissamphibia The Lissamphibia is a group of tetrapods that includes all modern amphibians. Lissamphibians consist of three living groups: the Salientia (frogs, toads, and their extinct relatives), the Caudata (salamanders, newts, and their extinct relativ ...
. Lissamphibians appear to have arisen in the Permian.
Molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleo ...
estimates place the first lissamphibian in the Late Carboniferous, but the first member of Batrachia (frogs and salamanders, but not caecilians) is estimated to have appeared in the
Middle Permian The Guadalupian is the second and middle series/ epoch of the Permian. The Guadalupian was preceded by the Cisuralian and followed by the Lopingian. It is named after the Guadalupe Mountains of New Mexico and Texas, and dates between 272.95 ± ...
using the same technique. Using fossil evidence, there are three main theories for the origin of modern amphibians. One is that they evolved from dissorophoid temnospondyls. Another is that they evolved from lepospondyls, most likely the
lysorophia Lysorophia is an order of fossorial Carboniferous and Permian tetrapods within the Recumbirostra. Lysorophians resembled small snakes, as their bodies are extremely elongate. There is a single family, the Molgophidae (previously known as Lysoroph ...
ns. A third hypothesis is that caecilians descended from lepospondyls and frogs and salamanders evolved from dissorophoids. Recently, the theory that temnospondyls were the ancestors of all lissamphibians has gained wide support. The skull morphology of some small temnospondyls has been compared to those of modern frogs and salamanders, but the presence of bicuspid,
pedicellate teeth Pedicellate teeth are a tooth morphology today unique to modern amphibians, but also seen in a variety of extinct labyrinthodonts "Labyrinthodontia" (Greek, 'maze-toothed') is an informal grouping of extinct predatory amphibians which were major ...
in small, paedomorphic or immature temnospondyls has been cited as the most convincing argument in favor of the temnospondyl origin of lissamphibians. Seen in lissamphibians and many dissorophoid temnospondyls, pedicellate teeth have calcified tips and bases. During the development of most tetrapods, teeth begin to calcify at their tips. Calcification normally proceeds downward to the base of the tooth, but calcification from the tip stops abruptly in pedicellate teeth. Calcification resumes at the base, leaving an area in the center of the tooth uncalcified. This pattern is seen in living amphibians and fossils. The dissorophoid family
Amphibamidae The Amphibamidae are an extinct family of dissorophoid temnospondyls known from Late Carboniferous-Early Permian strata in the United States. Classification Amphibamidae has traditionally included small-bodied, terrestrial dissorophoids. The ...
is thought to be most closely related to Lissamphibia. In 2008, an amphibamid called '' Gerobatrachus hottoni'' was named from
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
and was nicknamed the "frogamander" for its frog-like head and salamander-like body. It was thought to be the most closely related temnospondyl to lissamphibians and was placed as the
sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and ...
of the group in a phylogenetic analysis. Another species of amphibamid called '' Doleserpeton annectens'' is now thought to be even more closely related to lissamphibians. Unlike ''Gerobatrachus'', ''Doleserpeton'' was known since 1969, and the presence of pedicellate teeth in its jaws has led some paleontologists to conclude soon after its naming that it was a relative of modern amphibians. It was first described as a "protolissamphibian", and the specific name ''annectens'' means "connecting" in reference to its inferred transitional position between temnospondyls and lissamphibians. The structure of its tympanum, a disk-like membrane that functions like an ear drum, is similar to that of frogs and has also been used as evidence for a close relationship. Other features including the shape of the
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...
and the back of the skull, the short ribs, and the smooth skull surface also point to it being a closer relative of lissamphibians than is ''Gerobatrachus''. Below is a cladogram modified from Sigurdsen and Bolt (2010) showing the relationships of ''Gerobatrachus'', ''Doleserpeton'', and Lissamphibia: ''
Chinlestegophis ''Chinlestegophis'' is a diminutive Late Triassic stereospondyl that has been interpreted as a putative stem caecilian, a living group of legless burrowing amphibians. If ''Chinlestegophis'' is indeed both an advanced stereospondyl and a relative ...
'', a putative Triassic
stereospondyl The Stereospondyli are a group of extinct temnospondyl amphibians that existed primarily during the Mesozoic period. They are known from all seven continents and were common components of many Triassic ecosystems, likely filling a similar ecologi ...
considered to be related to metoposauroids such as ''
Rileymillerus ''Rileymillerus'' is an extinct genus of temnospondyl amphibian from the Late Triassic Post Quarry in the Dockum Group of Texas that was described by John Bolt and Sankar Chatterjee in 2000. The holotype, a nearly complete skull with articulated ...
'', has been noted to share many features with
caecilian Caecilians (; ) are a group of limbless, vermiform or serpentine amphibians. They mostly live hidden in the ground and in stream substrates, making them the least familiar order of amphibians. Caecilians are mostly distributed in the tropics o ...
s, a living group of legless burrowing amphibians. If ''Chinlestegophis'' is indeed both an advanced stereospondyl and a relative of caecilians, this means that although all lissamphibians are descended from temnospondyls, the different groups would have descended from different branches of the temnospondyl family tree. Anurans and urodelans would therefore be surviving dissorophoids while apodans (caecilians) are surviving stereospondyls.


Paleobiology


Metabolism and gas exchange

A study on the fully aquatic '' Archegosaurus'' shows that its heat balance, gas exchange, osmoregulation, and digestion were more similar to those of fish than those of modern aquatic amphibians like salamanders.


Feeding

Although the earliest temnospondyls were primarily semiaquatic, they had the ability to feed on land. Later, eryopoids and dissorophoids, some well adapted to terrestrial life, also fed on land. Some eryopoids became better adapted toward life in water and shifted their diets toward aquatic organisms. The first primarily aquatic feeders were archegosaurs in the Permian. Trematosaurs and capitosaurs became independently aquatic and also returned to this type of feeding. Most aquatic stereospondyls have flattened heads. When feeding, they probably opened their mouths by lifting their skulls instead of lowering their lower jaws. The jaw mechanics of the plagiosaurid ''
Gerrothorax ''Gerrothorax'' ("wicker chest") is an extinct genus of temnospondyl amphibian from the Triassic period of Greenland, Germany, Poland, Sweden, and possibly Thailand. It is known from a single species, ''G. pulcherrimus'', although several other ...
'' is well known, and is one of the most highly adapted. ''Gerrothorax'' is thought to have lifted its skull to around 50° above horizontal through the flexing of the atlanto-occipital joint between the occipital condyles of the skull and the
atlas An atlas is a collection of maps; it is typically a bundle of maps of Earth or of a region of Earth. Atlases have traditionally been bound into book form, but today many atlases are in multimedia formats. In addition to presenting geogra ...
vertebra of the neck. As the skull is raised, the quadrate bone pushes forward and causes the lower jaw to protrude outward. Other stereospondyls probably also lifted their skulls, but they are not as well adapted for such movement. D.M.S. Watson was the first to suggest skull lifting as a means of feeding in temnospondyls. He envisioned that ''Mastodonsaurus'', a much larger temnospondyl than ''Gerrothorax'', was able to make the same movement. Paleontologist A.L. Panchen also supported the idea in 1959, suggesting that ''
Batrachosuchus ''Batrachosuchus'' is a genus of temnospondyl amphibian that existed from the Early to Middle Triassic of Southern Africa ( Ntawere Formation of Zambia and Burgersdorp Formation of South Africa) and the Blina Shale of Australia Austr ...
'' also fed in this way. At the time it was thought that these temnospondyls lifted their heads with strong jaw muscles, but it is now thought that they used larger muscles in the neck that were attached to the large pectoral girdle. ''Plagiosuchus'', a close relative of ''Gerrothorax'', also has a hyobranchial skeleton that muscles may have attached to. ''Plagiosuchus'' has very small teeth and a large area for muscle attachment behind the skull, suggesting that it could suction feed by rapidly opening its mouth. Unlike semiaquatic temnospondyls, terrestrial temnospondyls have skulls that are adapted for biting land-living prey. The sutures between the bones of the skull in the dissorophoid ''
Phonerpeton ''Phonerpeton'' is an extinct genus of dissorophoid temnospondyl within the family Trematopidae that is known from the early Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of ...
'' are able to withstand a high degree of compression. Compressive forces would have been experienced when biting down on prey. Earlier aquatic tetrapods and tetrapod ancestors differ from temnospondyls like ''Phonerpeton'' in that their skulls were also built to withstand tension. This tension would have been experienced during suction feeding underwater. Temnospondyls like ''Phonerpeton'' were among the first tetrapods that were almost exclusively terrestrial and fed by biting.


Reproduction

Temnospondyls, like all amphibians, reproduced in aquatic environments. Most temnospondyls probably reproduced through
external fertilization External fertilization is a mode of reproduction in which a male organism's sperm fertilizes a female organism's egg outside of the female's body. It is contrasted with internal fertilization, in which sperm are introduced via insemination and then ...
. Like most living frogs, female temnospondyls would have laid masses of eggs in water while males released sperm to fertilize them. Several fossils were described from the Early Permian of Texas in 1998 that may be egg masses of dissorophoid temnospondyls. They were the first known fossils of amphibian eggs. The fossils consist of small disks with thin membranes that are probably
vitelline membrane The vitelline membrane or vitelline envelope is a structure surrounding the outer surface of the plasma membrane of an ovum (the oolemma) or, in some animals (e.g., birds), the extracellular yolk and the oolemma. It is composed mostly of protein f ...
s and halo-like areas surrounding them that are most likely mucous coatings. They are attached to plant fossils, suggesting that these temnospondyls laid eggs on aquatic plants much like modern frogs. The mucous membranes show that the eggs were laid by amphibians, not fish (their eggs lack mucous), but the type of amphibian that laid them cannot be known because no body fossils are preserved with the eggs. The eggs are thought to be from dissorophoids because they are likely to be close relatives of modern amphibians, and probably had similar reproductive strategies. They are also the most common amphibians from the deposit in which the eggs were found. One temnospondyl, the dvinosaur '' Trimerorhachis'', may have brooded young in an area between the gills called the pharyngeal pouch. Small bones belonging to younger ''Trimerorhachis'' individuals have been found in these pouches. The living Darwin's Frog is also a mouth brooder and would be the closest modern analogue to ''Trimerorhachis'' if it cared for its young in this way. An alternative possibility is that ''Trimerorhachis'' was cannibalistic, eating its young like many amphibians do today. If this was the case, the bones of these smaller individuals were originally located in the throat and were pushed into the pharyngeal pouch as the animal fossilized. Body impressions of Early Carboniferous temnospondyls from Pennsylvania suggest that some terrestrial temnospondyls mated on land like some modern amphibians. They reproduced through
internal fertilization Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For inte ...
rather than mating in water. The presence of three individuals in one block of sandstone shows that the temnospondyls were gregarious. The head of one individual rests under the tail of another in what may be a courtship display. Internal fertilization and similar courtship behavior are seen in modern salamanders.


Growth

While most types of temnospondyls are distinguished on the basis of features in mature specimens, several are known from juvenile and
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
l specimens.
Metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
is seen in dissorophoids, eryopids, and zatrachydids, with aquatic larvae developing into adults capable of living on land. Several types of dissorophoids, such as branchiosaurids, do not fully metamorphose, but retain features of juveniles such as external gills and small body size in what is known as
neoteny Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the physiological, or somatic, development of an organism, typically an animal. Neoteny is found in modern humans compare ...
. Dvinosaurians and the plagiosaurid ''
Gerrothorax ''Gerrothorax'' ("wicker chest") is an extinct genus of temnospondyl amphibian from the Triassic period of Greenland, Germany, Poland, Sweden, and possibly Thailand. It is known from a single species, ''G. pulcherrimus'', although several other ...
'' also retained gills, although recent studies found that (at least as adults) their gills were internal like those of fish, rather than external like those of salamanders. Temnospondyl larvae are often distinguished by poorly developed bones and the presence of a hyobranchial apparatus, a series of bones that
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they ar ...
s would attach to in life. However, some fully mature temnospondyls also possess hyobranchial bones but did not have external gills. A dense covering of scales is also seen in larvae and adults. Major body changes occur in metamorphosis, including the reshaping and strengthening of skull bones, the thickening of postcranial bones, and an increase in body size. Temnospondyls like ''
Sclerocephalus ''Sclerocephalus'' is an extinct genus of temnospondyl amphibian from the lowermost Permian of Germany and Czech Republic with four valid species, including the type species ''S. haeuseri''. It is one of the most completely preserved and most abu ...
'' are known from both large adult specimens and small larvae, showing an extreme change in body shape. In these species, the shape and proportions of skull bones change in the early stages of development. The ornamentation on the surface of the skull roof also develops at this time. Small, regularly spaced pits are the first to form, followed by larger ridges. As development continues, the external gills disappear. Small teeth that once covered the
palate The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly separ ...
are lost. The postcranial skeleton does not develop at the same rate as the skull, with
ossification Ossification (also called osteogenesis or bone mineralization) in bone remodeling is the process of laying down new bone material by cells named osteoblasts. It is synonymous with bone tissue formation. There are two processes resulting in ...
(the replacement of
cartilage Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck ...
by bone) happening more slowly. Vertebrae and limb bones are poorly developed, ribs and fingers are absent in the early stages, and the scapulocoracoid and
ischium The ischium () form ...
are entirely absent through most of development. Once maturity is reached, most bones have fully formed and growth rate slows. The bones of some temnospondyls like ''
Dutuitosaurus ''Dutuitosaurus'' is a genus of metoposaurids, a group of amphibians that lived during the Late Triassic period. ''Dutuitosaurus'' was discovered in the early 1960s in Morocco and is known from the lower t5 units of the Timezgadiouine Formation ...
'' show growth marks, possibly an indication that growth rate varied with the change in seasons. Fossils of temnospondyls like ''Metoposaurus'' and ''
Cheliderpeton ''Cheliderpeton'' (often misspelled ''Chelyderpeton'') is an extinct genus of temnospondyl amphibian. It lived during the Early Permian in what is now Europe. Fossils have been found from the Ruprechtice horizon of the Intrasudetic Basin of Bo ...
'' show that individuals grew larger past maturity. The oldest individuals usually have more pitting on their skulls with deeper sulci. One group of temnospondyls, the
Branchiosauridae Branchiosauridae is an extinct family of small amphibamiform temnospondyls with external gills and an overall juvenile appearance. The family has been characterized by hundreds of well-preserved specimens from the Permo-Carboniferous of Middle ...
, is also known from larval specimens. Branchiosaurids like ''Branchiosaurus'' and '' Apateon'' are represented by many fossils preserving skin and external gills. An entire growth series is exhibited in the wide range of sizes among specimens, but the lack of terrestrially adapted adult forms suggests that these temnospondyls were neotenic. Unlike other temnospondyls, their postcranial skeletons developed quickly but were still partly
cartilaginous Cartilage is a resilient and smooth type of connective tissue. In tetrapods, it covers and protects the ends of long bones at the joints as articular cartilage, and is a structural component of many body parts including the rib cage, the neck a ...
when fully mature. Adults likely had an aquatic lifestyle similar to juveniles. Recently, large specimens of ''Apateon gracilis'' were described with adaptations toward a terrestrial lifestyle, indicating that not all branchiosaurs were neotenic. Studies of temnospondyl development have reached differing conclusions regarding what forms of gills were present in temnospondyls which possessed the organs. Although some species possessed external gills which were preserved as soft tissue, for many groups the type of gill can only be inferred from the structure of the bones which would have supported them. Scientists have disagreed on what these bones imply. Scientists who compare temnospondyls to fish find that the bones correlate with internal gills, while those who compare them closely to salamanders consider the bones to correlate with external gills. This conundrum, known as Bystrow's paradox, has made it difficult to assess gills in temnospondyls. Bystrow's paradox was finally resolved by a 2010 study. This study found that grooved ceratobrachnial structures (components of the branchial arches) are correlated with internal gills. Ancient tetrapods which preserved grooved ceratobranchials, such as the dvinosaur ''
Dvinosaurus ''Dvinosaurus'' is an extinct genus of amphibious temnospondyls localized to regions of western and central Russia during the middle and late Permian, approximately 265-254 million years ago. Its discovery was first noted in 1921 by Russian pa ...
'', probably only had internal gills as adults. Nevertheless, external gills are known to have been conclusively present in at least some temnospondyls. However, these situations only occur in larval specimens or members of specialized groups such as the branchiosaurids. One living species of
lungfish Lungfish are freshwater vertebrates belonging to the order Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, i ...
(''
Lepidosiren The South American lungfish (''Lepidosiren paradoxa'') is the single species of lungfish found in swamps and slow-moving waters of the Amazon, Paraguay, and lower Paraná River basins in South America. Notable as an obligate air-breather, it is t ...
'') has external gills as larvae which transform into internal gills as adults. Despite adult dvinosaur specimens having skeletal features correlated with internal gills, some larval specimens of another dvinosaur, '' Isodectes'' preserved soft tissue external gills. Thus, the gill development of dvinosaurs (and presumably other temnospondyls) mirrored that of ''Lepidosiren''. Despite this feature likely being an example of convergent evolution (as other lungfish exclusively possessed internal gills), it still remains a useful gauge for how temnospondyl gills developed. Thus, even temnospondyls which were aquatic and possessed gills as adults (such as dvinosaurs) only had external gills as larvae. While most temnospondyls are aquatic in early stages of life, most metoposaurids appear to have been terrestrial in their juvenile stage. Like other Mesozoic temnospondyls, adult metoposaurids were adapted to a semiaquatic lifestyle. Their bones are not highly developed for movement on land. The cross-sectional thickness of limb bones in adult metoposaurids shows that they could not withstand the stress of terrestrial locomotion. Juvenile individuals have bones that are thick enough to withstand this stress, and could probably move about on land. To maintain a terrestrial lifestyle, a temnospondyl's limb bones would have to thicken with positive
allometry Allometry is the study of the relationship of body size to shape, anatomy, physiology and finally behaviour, first outlined by Otto Snell in 1892, by D'Arcy Thompson in 1917 in '' On Growth and Form'' and by Julian Huxley in 1932. Overview Allom ...
, meaning that they would grow at a greater rate than the rest of the body. This is not the case in metoposaurids, meaning that as their bodies grew larger they became less adapted toward a terrestrial lifestyle.


Hearing

Temnospondyls and other early tetrapods have rounded otic notches in the back of the skull that project into the cheek region. In life, the otic notch would have been covered by a membrane called the tympanum, which is seen as a disk-like area in living frogs. The tympanum is involved in hearing, and is similar to the ear drum of more advanced tetrapods. It was traditionally thought that the tympanum developed very early in tetrapod evolution as a hearing organ and progressed to form the eardrum of amniotes. Thus, temnospondyls possessed a hearing system supposedly ancestral to that of living amphibians and reptiles. Frogs and all other living tetrapods have a rod-like bone called the stapes that aids in hearing by transferring vibrations from the ear drum —or homologous tympanum— to the
inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in th ...
. Temnospondyls also have a stapes, which projects into the otic cavity. The stapes likely evolved from the
hyomandibula The hyomandibula, commonly referred to as hyomandibular one( la, os hyomandibulare, from el, hyoeides, "upsilon-shaped" (υ), and Latin: mandibula, "jawbone") is a set of bones that is found in the hyoid region in most fishes. It usually plays ...
of lobe-finned fishes. The positioning of the stapes and the shape of the otic region suggests that the tympani of temnospondyls and frogs are homologous, but the tympani of these amphibians are no longer considered homologous with the hearing systems of reptiles, birds, and mammals. Therefore, ear structures in temnospondyls were not ancestral to those of all other tetrapods. The ability of the tympanum and stapes to effectively transmit vibrations is called
impedance matching In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize si ...
. Early tetrapods like temnospondyls have thick stapes with poor impedance matching, so it is now thought that they were not used for hearing. Instead, these thick stapes may have functioned to support the tissue that covers the otic notch. Early temnospondyls, like ''
Dendrerpeton ''Dendrerpeton'' (from el, δένδρον , 'tree' and el, ἑρπετόν , 'creeping thing') is a genus of an extinct group of temnospondyl amphibians. Its fossils have been found primarily in the Joggins Formation of Eastern Canada and in I ...
'', could not hear airborne sound but would have been able to detect vibration in the ground. Later temnospondyls like ''Doleserpeton'' had otic regions adapted to hearing. ''Doleserpeton'' has a structure in the inner ear called the
perilymphatic duct In the anatomy of the human ear, the perilymphatic duct is where the perilymphatic space (vestibule of the ear) is connected to the subarachnoid space. This works as a type of shunt to eliminate excess perilymph fluid from the perilymphatic spac ...
, which is also seen in frogs and is associated with hearing. Its stapes is also a better transmitter of sound. The hearing system of ''Doleserpeton'' and related temnospondyls was able to detect airborne sound and may have been ancestral to that of living amphibians.


Notes

  1. Owen placed ''Labyrinthodon'' in
    Batrachia The Batrachia are a clade of amphibians that includes frogs and salamanders, but not caecilians nor the extinct allocaudates. The name Batrachia was first used by French zoologist Pierre André Latreille in 1800 to refer to frogs, but has more ...
    , a group that includes frogs, and classified Batrachia within Reptilia. What are today classified as reptiles (lizards, snakes, crocodilians and turtles) were called
    sauria Sauria is the clade containing the most recent common ancestor of archosaurs (such as crocodilians, dinosaurs, etc.) and lepidosaurs ( lizards and kin), and all its descendants. Since most molecular phylogenies recover turtles as more closely ...
    n reptiles.


References


External links


Temnospondyli
Tree of Life project page on temnospondyls.

Palaeos Palaeos.com is a web site on biology, paleontology, phylogeny and geology and which covers the history of Earth. The site is well respected and has been used as a reference by professional paleontologists such as Michael J. Benton, the professor of ...
page on temnospondyls. {{Taxonbar, from=Q131447 Early Cretaceous extinctions Mississippian first appearances Fossil taxa described in 1883 Taxa named by Karl Alfred Ritter von Zittel Prehistoric animal orders