135-524: 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 that existed during the Mesozoic in ecological niches broadly similar to those of modern crocodiles , and some grew to very large sizes. At 6 meters in length,
270-588: A bone common in stem tetrapods, is only found in some late Paleozoic taxa like certain edopoids and dvinosaurs . 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 lack notches entirely. The palate of temnospondyls generally consists of
405-510: A close similarity to crocodiles, although they lacked the armor characteristic of the latter group. These temnospondyls included the largest-known batrachomorph, the over 5.5-meter-long Prionosuchus of Brazil. The stereospondyl record is almost exclusively confined to rhinesuchids . As temnospondyls continued to flourish and diversify in the Late Permian (260.4–251.0 Mya), a major group called Stereospondyli became more dependent on life in
540-404: A counterpart to it), but Stereospondyli is still considered valid. Below is a simplified taxonomy of temnospondyls showing currently recognized groups: Class Amphibia In one of the earliest phylogenetic analyses of the group, Gardiner (1983) recognized five characteristics that made Temnospondyli a clade : a bone at the back of the skull, the parasphenoid , is connected to another bone on
675-614: A full complement of limbs. Similar considerations apply to caecilians and aquatic mammals . Newer taxonomy is frequently based on cladistics instead, giving a variable number of major "branches" ( clades ) of the tetrapod family tree . As is the case throughout evolutionary biology today, there is debate over how to properly classify the groups within Tetrapoda. Traditional biological classification sometimes fails to recognize evolutionary transitions between older groups and descendant groups with markedly different characteristics. For example,
810-501: 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 , small holes in their skulls behind their eye sockets. Archegosaurus , Dendrerpeton , Eryops and Trimerorhachis were placed in this group and were considered to be the most primitive members of Reptilia. Their rhachitomous vertebrae, notochord and lack of occipital condyles (which attached
945-399: 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
1080-631: A membrane ensuring gas exchange out of water and can therefore be laid on land. Amphibians and amniotes were affected by the Carboniferous rainforest collapse (CRC), an extinction event that occurred around 307 million years ago. The sudden collapse of a vital ecosystem shifted the diversity and abundance of major groups. Amniotes and temnospondyls in particular were more suited to the new conditions. They invaded new ecological niches and began diversifying their diets to include plants and other tetrapods, previously having been limited to insects and fish. In
1215-453: A more recent common ancestry with living amphibians than with living amniotes (reptiles, birds, and mammals). Reptiliomorphs are all animals sharing a more recent common ancestry with living amniotes than with living amphibians. Gaffney (1979) provided the name Neotetrapoda to the crown group of tetrapods, though few subsequent authors followed this proposal. Tetrapoda includes three living classes: amphibians, reptiles, and mammals. Overall,
1350-543: A pair of vestigial spurs that are remnants of the hindlimbs . Tetrapods evolved from a group of primitive semiaquatic animals known as the Tetrapodomorpha which, in turn, evolved from ancient lobe-finned fish ( sarcopterygians ) around 390 million years ago in the Middle Devonian period . Tetrapodomorphs were transitional between lobe-finned fishes and true four-limbed tetrapods, though most still fit
1485-466: A particularly high diversity of dissorophoids. Middle Permian records of temnospondyls are relatively sparse, and some of these are debated as a result of the uncertain age and correlation of different deposits in North America (Chickasha, Flowerpot Formations), Niger (Moradi Formation), Brazil (Rio do Rasto Formation), and Russia (Mezen complex) and the subsequent controversy over Olson's Gap, but there
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#17328809444091620-509: A reference to the wide, flat heads of temnospondyls and other early tetrapods. During this time, paleontologists considered temnospondyls to be amphibians because they possessed three main features: gill arches 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
1755-483: A remnant of the limbs of their distant ancestors. Others returned to being amphibious or otherwise living partially or fully aquatic lives, the first during the Carboniferous period, others as recently as the Cenozoic . One fundamental subgroup of amniotes, the sauropsids , diverged into the reptiles : lepidosaurs (lizards, snakes, and the tuatara ), archosaurs ( crocodilians and dinosaurs , of which birds are
1890-400: A rigid spine. In conjunction with robust forelimbs and shoulder girdle, both Tiktaalik and Ichthyostega may have had the ability to locomote on land in the manner of a seal, with the forward portion of the torso elevated, the hind part dragging behind. Finally, Tiktaalik fin bones are somewhat similar to the limb bones of tetrapods. However, there are issues with positing Tiktaalik as
2025-401: A separate subclass, but they are more closely related to mammals than to living reptiles. Considerations like these have led some authors to argue for a new classification based purely on phylogeny , disregarding the anatomy and physiology. Tetrapods evolved from early bony fishes (Osteichthyes), specifically from the tetrapodomorph branch of lobe-finned fishes ( Sarcopterygii ), living in
2160-474: 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 proposed that
2295-497: A single common ancestor. In this sense, Tetrapoda can also be defined as the "clade of limbed vertebrates", including all vertebrates descended from the first limbed vertebrates. A portion of tetrapod workers, led by French paleontologist Michel Laurin , prefer to restrict the definition of tetrapod to the crown group . A crown group is a subset of a category of animal defined by the most recent common ancestor of living representatives. This cladistic approach defines "tetrapods" as
2430-486: 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 named the animal Batrachosaurus in 1837. In 1841, the English paleontologist Richard Owen referred to the genus as Labyrinthodon to describe its highly folded or labyrinthine teeth. Owen thought that
2565-452: A subset of animals related to, but not within, the crown group. The stem and crown group together are combined into the total group , given the name Tetrapodomorpha , which refers to all animals closer to living tetrapods than to Dipnoi ( lungfishes ), the next closest group of living animals. Many early tetrapodomorphs are clearly fish in ecology and anatomy, but later tetrapodomorphs are much more similar to tetrapods in many regards, such as
2700-449: A subset), turtles , and various other extinct forms. The remaining group of amniotes, the synapsids , include mammals and their extinct relatives. Amniotes include the only tetrapods that further evolved for flight—such as birds from among the dinosaurs, the extinct pterosaurs from earlier archosaurs, and bats from among the mammals. The precise definition of "tetrapod" is a subject of strong debate among paleontologists who work with
2835-555: A sudden opening of the upper jaw and sucking in fish or other small animals. In the Carnian stage of the Late Triassic (237.0–227.0 Mya), capitosauroids were joined by the superficially very similar Metoposauridae . 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 gills , and adapted to life at
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#17328809444092970-419: 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 larval 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
3105-468: A tetrapod ancestor. For example, it had a long spine with far more vertebrae than any known tetrapod or other tetrapodomorph fish. Also the oldest tetrapod trace fossils (tracks and trackways) predate it by a considerable margin. Several hypotheses have been proposed to explain this date discrepancy: 1) The nearest common ancestor of tetrapods and Tiktaalik dates to the Early Devonian. By this hypothesis,
3240-614: A variety of diets. The following table shows summary estimates for each tetrapod class from the IUCN Red List of Threatened Species , 2014.3, for the number of extant species that have been described in the literature, as well as the number of threatened species . The classification of tetrapods has a long history. Traditionally, tetrapods are divided into four classes based on gross anatomical and physiological traits. Snakes and other legless reptiles are considered tetrapods because they are sufficiently like other reptiles that have
3375-426: 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. Very little is known of the soft tissue of temnospondyls because
3510-570: A variety of marine organisms and was apparently salt water. The average water temperature was 30 degrees C (86 F). The second oldest evidence for tetrapods, also tracks and trackways, date from ca. 385 Mya ( Valentia Island , Ireland). The oldest partial fossils of tetrapods date from the Frasnian beginning ≈380 mya. These include Elginerpeton and Obruchevichthys . Some paleontologists dispute their status as true (digit-bearing) tetrapods. All known forms of Frasnian tetrapods became extinct in
3645-468: Is a cladogram from Ruta et al. (2003) placing Temnospondyli within crown Tetrapoda: Acanthostega [REDACTED] Ichthyostega [REDACTED] Tulerpeton [REDACTED] Colosteidae [REDACTED] Crassigyrinus [REDACTED] Whatcheeriidae [REDACTED] Baphetidae Tetrapod A tetrapod ( / ˈ t ɛ t r ə ˌ p ɒ d / ; from Ancient Greek τετρα- (tetra-) 'four' and πούς (poús) 'foot')
3780-444: Is a stub . You can help Misplaced Pages by expanding it . This article related to a Triassic animal is a stub . You can help Misplaced Pages by expanding it . Temnospondyl See below Temnospondyli (from Greek τέμνειν, temnein 'to cut' and σπόνδυλος, spondylos 'vertebra') or temnospondyls is a diverse ancient order of small to giant tetrapods —often considered primitive amphibians —that flourished worldwide during
3915-545: Is a general consensus that at least some of these records are Guadalupian in age. Records of rhinesuchids from the Eodicynodon and Tapinocephalus Assemblage Zones of South Africa are less controversial. Additional records are known from Brazil, China, Turkey, and the Isheevo complex of Russia. A mixture of taxa are represented, including stereospondylomorphs ( Konzhukovia ) and rhinesuchid stereospondyls, as well as some of
4050-410: Is also still used in some specialist works like Fortuny et al. (2011). The taxonomy down to subclass level shown here is from Hildebrand and Goslow (2001): This classification is the one most commonly encountered in school textbooks and popular works. While orderly and easy to use, it has come under critique from cladistics . The earliest tetrapods are grouped under class Amphibia, although several of
4185-708: Is any four- limbed vertebrate animal of the superclass Tetrapoda ( / t ɛ ˈ t r æ p ə d ə / ). Tetrapods include all extant and extinct amphibians and amniotes , with the latter in turn evolving into two major clades , the sauropsids ( reptiles , including dinosaurs and therefore birds ) and synapsids (extinct pelycosaurs , therapsids and all extant mammals , including humans ). Hox gene mutations have resulted in some tetrapods becoming limbless ( snakes , legless lizards , and caecilians ) or two-limbed ( cetaceans , moas , and some lizards ). Nevertheless, these limbless groups still qualify as tetrapods through their ancestry, and some retain
Capitosauria - Misplaced Pages Continue
4320-599: 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 scapulae / 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
4455-501: 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 that 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
4590-468: 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 an exclusive group (i.e. it includes Stereospondyli rather than being
4725-529: Is now placed as an early tetrapod outside Temnospondyli, and Rhombopholis is now considered a prolacertiform reptile. Later in the 19th century, temnospondyls were classified as various members of Stegocephalia , a name coined by the American paleontologist Edward Drinker Cope in 1868. Cope placed stegocephalians in the class Batrachia, the name then used for Amphibia . Stegocephalia means "roof-headed" in Greek ,
4860-465: Is separated from the skull, connected to the torso by muscle and other soft-tissue connections. The result is the appearance of the neck. This feature appears only in tetrapods and Tiktaalik , not other tetrapodomorph fishes. Tiktaalik also had a pattern of bones in the skull roof (upper half of the skull) that is similar to the end-Devonian tetrapod Ichthyostega . The two also shared a semi-rigid ribcage of overlapping ribs, which may have substituted for
4995-477: Is the amnion , which enables the eggs to retain their aqueous contents on land, rather than needing to stay in water. (Some amniotes later evolved internal fertilization , although many aquatic species outside the tetrapod tree had evolved such before the tetrapods appeared, e.g. Materpiscis .) Some tetrapods, such as snakes and caecilians , have lost some or all of their limbs through further speciation and evolution; some have only concealed vestigial bones as
5130-402: Is the earliest known tetrapod that may have had the ability to pull itself onto land and drag itself forward with its forelimbs. There is no evidence that it did so, only that it may have been anatomically capable of doing so. The publication in 2018 of Tutusius umlambo and Umzantsia amazana from high latitude Gondwana setting indicate that the tetrapods enjoyed a global distribution by
5265-538: Is thought to have stiffened the vertebral column in association with the relative terrestriality of this clade. Recent histological work has demonstrated that most of this hyperelongation is formed by the osteoderm capping the spine, and thus the sail of Platyhystrix is dissimilar to that of pelycosaurs in which it is entirely formed by the spine. 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
5400-462: 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 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 bones may have been an early solution to
5535-464: Is well understood, with fossils known from the larval stage, metamorphosis and maturity. Most temnospondyls were semiaquatic , 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 amphibians, many had characteristics such as scales and large armour-like bony plates (osteoderms) that generally distinguish them from
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5670-527: The Carboniferous , Permian and Triassic periods, with fossils being found on every continent. A few species continued into the Jurassic and Early Cretaceous periods, but all had gone extinct by the Late Cretaceous . 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
5805-514: The Eifelian stage of the Middle Devonian, 390 million years ago , although these traces have also been interpreted as the ichnogenus Piscichnus (fish nests/feeding traces). The adult tetrapods had an estimated length of 2.5 m (8 feet), and lived in a lagoon with an average depth of 1–2 m, although it is not known at what depth the underwater tracks were made. The lagoon was inhabited by
5940-629: The Late Devonian extinction , also known as the end-Frasnian extinction. This marked the beginning of a gap in the tetrapod fossil record known as the Famennian gap, occupying roughly the first half of the Famennian stage. The oldest near-complete tetrapod fossils, Acanthostega and Ichthyostega , date from the second half of the Fammennian. Although both were essentially four-footed fish, Ichthyostega
6075-405: The Late Devonian extinctions , also known as the end-Frasnian and end-Fammenian extinctions. These extinction events led to the disappearance of stem-tetrapods with fish-like features. When stem-tetrapods reappear in the fossil record in early Carboniferous deposits, some 10 million years later, the adult forms of some are somewhat adapted to a terrestrial existence. Why they went to land in
6210-460: The Permian period, amniotes became particularly well-established, and two important clades filled in most terrestrial niches: the sauropsids and the synapsids . The latter were the most important and successful Permian land animals, establishing complex terrestrial ecosystems of predators and prey while acquiring various adaptations retained by their modern descendants, the mammals. Sauropsid diversity
6345-1153: The Visean age of the Early Carboniferous . The specific aquatic ancestors of the tetrapods and the process by which they colonized Earth's land after emerging from water remains unclear. The transition from a body plan for gill -based aquatic respiration and tail -propelled aquatic locomotion to one that enables the animal to survive out of water and move around on land is one of the most profound evolutionary changes known. Tetrapods have numerous anatomical and physiological features that are distinct from their aquatic fish ancestors. These include distinct head and neck structures for feeding and movements, appendicular skeletons ( shoulder and pelvic girdles in particular) for weight bearing and locomotion, more versatile eyes for seeing, middle ears for hearing, and more efficient heart and lungs for oxygen circulation and exchange outside water. Stem-tetrapods and "fish-a-pods" were primarily aquatic . Modern amphibians , which evolved from earlier groups , are generally semiaquatic ;
6480-415: The tristichopterids (notably Eusthenopteron ), and more recently the elpistostegalians (also known as Panderichthyida) notably the genus Tiktaalik . A notable feature of Tiktaalik is the absence of bones covering the gills. These bones would otherwise connect the shoulder girdle with skull, making the shoulder girdle part of the skull. With the loss of the gill-covering bones, the shoulder girdle
6615-591: The 13.9-million year Tournaisian, the first stage of the Carboniferous period. Tetrapod-like vertebrates first appeared in the Early Devonian period, and species with limbs and digits were around by the Late Devonian. These early "stem-tetrapods" included animals such as Ichthyostega , with legs and lungs as well as gills, but still primarily aquatic and poorly adapted for life on land. The Devonian stem-tetrapods went through two major population bottlenecks during
6750-478: The 20th and 21st centuries, including the first occurrences from historically undersampled regions such as Antarctica, Lesotho, Japan, Namibia, New Zealand, Niger, and Türkiye. Temnospondyls first appeared in the Middle Mississippean ( Viséan ) around 330 million years ago (Mya) where the earliest appearances are Balanerpeton from Scotland and an indeterminate temnospondyl from Germany. During
6885-409: The Carboniferous, all of the non-stereospondylomorph clades appeared, including dendrerpetids , edopoids , 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
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#17328809444097020-616: The Cenozoic, similar to mammals. Following the great extinction event at the end of the Mesozoic, representatives of seven major groups of tetrapods persisted into the Cenozoic era. One of them, a group of semiaquatic reptiles known as the Choristodera , became extinct 11 million years ago for unclear reasons. The seven Cenozoic tetrapods groups are: Stem tetrapods are all animals more closely related to tetrapods than to lungfish, but excluding
7155-503: The French zoologist Pierre André Latreille recognized the large physiological differences at the beginning of the 19th century and split the herptiles into two classes, giving the four familiar classes of tetrapods: amphibians, reptiles, birds and mammals. With the basic classification of tetrapods settled, a half a century followed where the classification of living and fossil groups was predominantly done by experts working within classes. In
7290-548: The Mid-Triassic Mastodonsaurus giganteus is not only thought to have been the largest capitosaur, but possibly also the largest amphibian to have lived. The latest known remains are from the Rhaetian of Germany and are referred to Cyclotosaurus . Capitosauria was first named by Schoch and Milner (2000) and further described by Yates and Warren (2000), who assigned Lydekkerina and Mastodonsauroidea to it. It
7425-679: The Permian saw a major turnover in fauna during the Permian–Triassic extinction event . There was a protracted loss of species, due to multiple extinction pulses. Many of the once large and diverse groups died out or were greatly reduced. The diapsid reptiles (a subgroup of the sauropsids) strongly diversified during the Triassic , giving rise to the turtles , pseudosuchians (crocodilian ancestors), dinosaurs , pterosaurs , and lepidosaurs , along with many other reptile groups on land and sea. Some of
7560-533: The Triassic. Common ichnogenera include Batrachichnus and Limnopus . Temnospondyli was named by the German paleontologist Karl Alfred von Zittel 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
7695-420: 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 trematosaurs and capitosaurs , have no evidence of scales. They may have lost scales to make movement easier under water or to allow cutaneous respiration , the absorption of oxygen through
7830-441: The apomorphy-based definition is often supported by an equivalent cladistic definition. Cladistics is a modern branch of taxonomy which classifies organisms through evolutionary relationships, as reconstructed by phylogenetic analyses . A cladistic definition would define a group based on how closely related its constituents are. Tetrapoda is widely considered a monophyletic clade , a group with all of its component taxa sharing
7965-489: 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
8100-506: The best understood animals since earliest times. By Aristotle 's time, the basic division between mammals, birds and egg-laying tetrapods (the " herptiles ") was well known, and the inclusion of the legless snakes into this group was likewise recognized. With the birth of modern biological classification in the 18th century, Linnaeus used the same division, with the tetrapods occupying the first three of his six classes of animals. While reptiles and amphibians can be quite similar externally,
8235-503: The biodiversity of lissamphibians , as well as of tetrapods generally, has grown exponentially over time; the more than 30,000 species living today are descended from a single amphibian group in the Early to Middle Devonian. However, that diversification process was interrupted at least a few times by major biological crises, such as the Permian–Triassic extinction event , which at least affected amniotes. The overall composition of biodiversity
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#17328809444098370-482: The birds, which evolved from the dinosaurs, are defined as a separate group from them, because they represent a distinct new type of physical form and functionality. In phylogenetic nomenclature , in contrast, the newer group is always included in the old. For this school of taxonomy, dinosaurs and birds are not groups in contrast to each other, but rather birds are a sub-type of dinosaurs. The tetrapods, including all large- and medium-sized land animals, have been among
8505-517: The body plan expected of other lobe-finned fishes. The oldest fossils of four-limbed vertebrates (tetrapods in the broad sense of the word) are trackways from the Middle Devonian , and body fossils became common near the end of the Late Devonian , around 370–360 million years ago. These Devonian species all belonged to the tetrapod stem group , meaning that they were not directly related to any modern tetrapod group. Broad anatomical descriptors like "tetrapod" and "amphibian" can approximate some members of
8640-489: 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 , even inhabited Antarctica , which was covered in temperate forests at the time. Triassic temnospondyls were often the dominant semiaquatic animals in their environments. Large assemblages of Late Triassic metoposaurids with hundreds of individuals preserved together have been found in
8775-566: The characteristic Paleozoic non-amniote tetrapods, few survived into the Mesozoic. Temnospondyls briefly recovered in the Triassic, spawning the large aquatic stereospondyls and the small terrestrial lissamphibians (the earliest frogs, salamanders, and caecilians). However, stereospondyl diversity would crash at the end of the Triassic. By the Late Cretaceous, the only surviving amphibians were lissamphibians. Many groups of synapsids, such as anomodonts and therocephalians , that once comprised
8910-415: The classification of modern amphibians, they are either included in the crown group 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
9045-417: 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
9180-449: 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
9315-415: The contact between the postparietal and exoccipital at the back of the skull, small projections ( uncinate processes ) on the ribs , and a pelvic girdle with each side having a single iliac blade . These shared derived characteristics are called synapomorphies . Temnospondyls are placed as basal tetrapods in phylogenetic analyses, with their exact positioning varying between studies. Depending on
9450-560: The disuse of terms like Labyrinthodontia and Stegocephalia continues. Temnospondyls continue to be heavily involved in the debate over lissamphibian origins. As with evolutionary biology in general, computer-assisted phylogenetic methods have greatly facilitated phylogenetic inference of the relationships of both Temnospondyli at large and specific sub-groups. Other quantitative analyses have addressed morphometrics, biomechanics, Temnospondyls were also documented from an increasingly broad geographic and stratigraphic range in
9585-522: The dominant terrestrial fauna of the Permian, also became extinct during the Triassic. During the Jurassic, one synapsid group ( Cynodontia ) gave rise to the modern mammals , which survived through the rest of the Mesozoic to later diversify during the Cenozoic. The Cretaceous-Paleogene extinction event at the end of the Mesozoic killed off many organisms, including all the non-avian dinosaurs and nearly all marine reptiles. Birds survived and diversified during
9720-402: The dvinosaur Erpetosaurus , the capitosaur Mastodonsaurus and the trematosaur Microposaurus , tusks in the lower jaw pierce the palate and emerge through openings in the top of the skull. Temnospondyls' vertebrae 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
9855-405: The earliest members of the group. A majority of paleontologists use the term "tetrapod" to refer to all vertebrates with four limbs and distinct digits (fingers and toes), as well as legless vertebrates with limbed ancestors. Limbs and digits are major apomorphies (newly evolved traits) which define tetrapods, though they are far from the only skeletal or biological innovations inherent to
9990-428: The early 1930s, American vertebrate palaeontologist Alfred Romer (1894–1973) produced an overview, drawing together taxonomic work from the various subfields to create an orderly taxonomy in his Vertebrate Paleontology . This classical scheme with minor variations is still used in works where systematic overview is essential, e.g. Benton (1998) and Knobill and Neill (2006). While mostly seen in general works, it
10125-446: The early 20th century, when they were found to belong to a distinct taxon 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 ( frogs , salamanders and caecilians ), or whether
10260-726: The early to middle Devonian period . The first tetrapods probably evolved in the Emsian stage of the Early Devonian from Tetrapodomorph fish living in shallow water environments. The very earliest tetrapods would have been animals similar to Acanthostega , with legs and lungs as well as gills, but still primarily aquatic and unsuited to life on land. The earliest tetrapods inhabited saltwater, brackish-water, and freshwater environments, as well as environments of highly variable salinity. These traits were shared with many early lobed-finned fishes. As early tetrapods are found on two Devonian continents, Laurussia ( Euramerica ) and Gondwana , as well as
10395-567: The end of the Devonian and even extend into the high latitudes. The end-Fammenian marked another extinction, known as the end-Fammenian extinction or the Hangenberg event , which is followed by another gap in the tetrapod fossil record, Romer's gap , also known as the Tournaisian gap. This gap, which was initially 30 million years, but has been gradually reduced over time, currently occupies much of
10530-464: The entire animal would have been several meters in length (for reference, the largest living amphibian, Andrias , is about 1.8 meters in body length). Others are smaller and resemble salamanders, in particularly the amphibamiform and micromelerpetid dissorophoids. Skulls are generally parabolic to triangular in shape when viewed from above, and they were particularly flattened in semiaquatic to aquatic taxa, with dorsally facing orbits. The skull
10665-468: 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
10800-456: The eye or stomach. An amphibamiform specimen from the Mazon Creek locality was described as having toepad-like features. The holotype specimen of Arenaerpeton supinatus from the Triassic of New South Wales, Australia, displays extensive soft tissue, hinting at the girth of the animal in life. Trace fossils attributed to temnospondyls are fairly common, especially from the Carboniferous through
10935-446: The first place is still debated. During the early Carboniferous, the number of digits on hands and feet of stem-tetrapods became standardized at no more than five, as lineages with more digits died out (exceptions within crown-group tetrapods arose among some secondarily aquatic members). By mid-Carboniferous times, the stem-tetrapods had radiated into two branches of true ("crown group") tetrapods, one ancestral to modern amphibians and
11070-481: The first stages of their lives are as waterborne eggs and fish-like larvae known as tadpoles , and later undergo metamorphosis to grow limbs and become partly terrestrial and partly aquatic. However, most tetrapod species today are amniotes , most of which are terrestrial tetrapods whose branch evolved from earlier tetrapods early in the Late Carboniferous . The key innovation in amniotes over amphibians
11205-475: 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 . Mastodonsaurus and other similar animals were referred to as labyrinthodonts , named like Labyrinthodon for teeth that were highly folded in cross section. Owen's " Labyrinthodon Jaegeri " was later found at Guy's Cliffe , England by paleontologist William Buckland . Other specimens were found in
11340-448: 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
11475-496: 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 brought the name Temnospondyli back into use in the later 20th century. Säve-Söderbergh used the name Labyrinthodontia in a strict sense ( sensu stricto ) to refer to Rhachitomi and Stereospondyli, excluding Embolomeri. Romer agreed with this classification, but used
11610-486: The group. The first vertebrates with limbs and digits evolved in the Devonian , including the Late Devonian -age Ichthyostega and Acanthostega , as well as the trackmakers of the Middle Devonian -age Zachelmie trackways . Defining tetrapods based on one or two apomorphies can present a problem if these apomorphies were acquired by more than one lineage through convergent evolution . To resolve this potential concern,
11745-419: The groups are more closely related to amniotes than to modern day amphibians . Traditionally, birds are not considered a type of reptile, but crocodiles are more closely related to birds than they are to other reptiles, such as lizards. Birds themselves are thought to be descendants of theropod dinosaurs . Basal non-mammalian synapsids ("mammal-like reptiles") traditionally also sort under class Reptilia as
11880-475: 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 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
12015-482: The import of this disparity is also unclear. Many temnospondyls also have canal-like grooves in their skulls called sensory sulci , 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 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
12150-483: 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 a separate group of reptiliomorphs or stem-group tetrapods , with no particular affinities to temnospondyls. In 1888, von Zittel divided stegocephalians among three taxa: Lepospondyli, Temnospondyli and Stereospondyli . He placed microsaurs in Lepospondyli,
12285-588: 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
12420-408: The island of North China , it is widely supposed that early tetrapods were capable of swimming across the shallow (and relatively narrow) continental-shelf seas that separated these landmasses. Since the early 20th century, several families of tetrapodomorph fishes have been proposed as the nearest relatives of tetrapods, among them the rhizodonts (notably Sauripterus ), the osteolepidids ,
12555-710: 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 and enamel in their teeth. Branchiosauria included only a few forms, such as Branchiosaurus from Europe and Amphibamus 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 (although more detailed studies found it to be
12690-426: The latest occurrences of dissorophoids ( Anakamacops , Kamacops ). During the late Permian , increasing aridity and the diversification of reptiles contributed to a decline in terrestrial temnospondyls, but semiaquatic and fully aquatic stereospondylomorph temnospondyls continued to flourish, including the large Melosaurus of Eastern Europe. Other temnospondyls, such as archegosaurids , developed long snouts and
12825-579: The lineage is the closest to tetrapods, but Tiktaalik itself was a late-surviving relic. 2) Tiktaalik represents a case of parallel evolution. 3) Tetrapods evolved more than once. [REDACTED] Coelacanthiformes (coelacanths) [REDACTED] Dipnoi (lungfish) [REDACTED] †Tetrapodomorph fishes [REDACTED] Tetrapoda [REDACTED] The oldest evidence for the existence of tetrapods comes from trace fossils : tracks (footprints) and trackways found in Zachełmie , Poland, dated to
12960-481: The midline near the tip of the snout called the internarial fenestra / fontanelle; this may have housed a mucous 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 interparietals , that have developed in some temnospondyl taxa. The intertemporal,
13095-713: The midwestern United States, such as the Linton, Five Points and Mazon Creek lagerstätte , 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 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
13230-509: The modern groups arose from only one group ( dissorophoids ) 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. Whether temnospondyls are considered part of the tetrapod crown or stem thus depends on their inferred relationship to lissamphibians. In 2000, Adam Yates and Anne Warren defined
13365-494: The modern soft-bodied lissamphibians ( frogs and toads , newts , salamanders and caecilians ). Temnospondyls have been known since the early 19th century, and were initially thought to be reptiles . They were described at various times as batrachians , stegocephalians and labyrinthodonts , although these names are now rarely used. Animals now grouped in Temnospondyli were spread out among several amphibian groups until
13500-554: 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
13635-461: The name Temnospondyli as applying to the clade encompassing all organisms that are more closely related to Eryops than to the “ microsaur ” Pantylus . By this definition, if lissamphibians are temnospondyls and Pantylus is a reptiliomorph , the name Temnospondyli is synonymous with Batrachomorpha (a clade containing all organisms that are more closely related to modern amphibians than to mammals and reptiles). Rainer Schoch in 2013 defined
13770-415: The name Temnospondyli as applying to “[t]he least inclusive clade containing Edops craigi and Mastodonsaurus giganteus ”. Many temnospondyls are much larger than living amphibians, and superficially resemble crocodiles , which has led many taxa to be named with the suffix - suchus . The largest taxa, which were predominantly the Mesozoic stereospondyls, had skulls exceeding one meter in length, and
13905-414: The name Temnospondyli to avoid confusion with Labyrinthodontia in its wider sense ( sensu lato ). Unlike modern temnospondyl classification, however, Romer included the primitive Ichthyostegalia in the group. More recent study of temnospondyls has largely focused on their paleobiology and resolving their internal relationships. With a few exceptions, the monophyly of Temnospondyli is not questioned, and
14040-412: The nearest common ancestor of all living amphibians (the lissamphibians) and all living amniotes (reptiles, birds, and mammals), along with all of the descendants of that ancestor. In effect, "tetrapod" is a name reserved solely for animals which lie among living tetrapods, so-called crown tetrapods. This is a node-based clade , a group with a common ancestry descended from a single "node" (the node being
14175-408: The nearest common ancestor of living species). Defining tetrapods based on the crown group would exclude many four-limbed vertebrates which would otherwise be defined as tetrapods. Devonian "tetrapods", such as Ichthyostega and Acanthostega , certainly evolved prior to the split between lissamphibians and amniotes, and thus lie outside the crown group. They would instead lie along the stem group ,
14310-726: The new Triassic reptiles would not survive into the Jurassic , but others would flourish during the Jurassic. Lizards , turtles, dinosaurs, pterosaurs, crocodylomorphs , and plesiosaurs were particular beneficiaries of the Triassic-Jurassic transition. Birds , a particular subset of theropod dinosaurs capable of flight via feathered wings, evolved in the Late Jurassic. In the Cretaceous , snakes developed from lizards, rhynchocephalians (tuataras and kin) declined, and modern birds and crocodilians started to establish themselves. Among
14445-404: 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 in 1848, Trematosaurus in 1849, Baphetes and Dendrerpeton in 1853, Capitosaurus in 1858, and Dasyceps in 1859. Baphetes
14580-421: The only known batrachomorphs to do so with the exception of the modern crab-eating frog . Another group, the capitosauroids , included medium-sized and large animals 2.3 to 4 m (7.5 to 13.1 ft) 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
14715-571: 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 , had lost their pleurocentra, and
14850-407: The other ancestral to amniotes. Modern amphibians are most likely derived from the temnospondyls , a particularly diverse and long-lasting group of tetrapods. A less popular proposal draws comparisons to the " lepospondyls ", an eclectic mixture of various small tetrapods, including burrowing, limbless, and other bizarrely-shaped forms. The reptiliomorphs (sometimes known as " anthracosaurs ") were
14985-734: 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 , 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
15120-452: 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 , 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 and edaphosaurids , remains enigmatic, but it
15255-454: The presence of limbs and digits. Laurin's approach to the definition of tetrapods is rooted in the belief that the term has more relevance for neontologists (zoologists specializing in living animals) than paleontologists (who primarily use the apomorphy-based definition). In 1998, he re-established the defunct historical term Stegocephali to replace the apomorphy-based definition of tetrapod used by many authors. Other paleontologists use
15390-458: 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 , plagiosaurine plagiosaurids ), and
15525-636: The red sandstone of Warwickshire . 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 (a unit of rocks that dates to the Late Triassic ) were younger than more advanced reptiles in the Magnesian and Zechstein , which are Late Permian in age. Owen used these fossils to counter
15660-430: The relatives and ancestors of the amniotes (reptiles, mammals, and kin). The first amniotes are known from the early part of the Late Carboniferous . All basal amniotes had a small body size, like many of their contemporaries, though some Carboniferous tetrapods evolved into large crocodile-like predators, informally known as " labyrinthodonts ". Amphibians must return to water to lay eggs; in contrast, amniote eggs have
15795-487: 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 . 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
15930-451: The skin. Several groups of temnospondyls have large bony plates ( osteoderms ) on their backs. One temnospondyl, Peltobatrachus , 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 also have armor, although it only covers the midline of the back with one or two narrow rows of plates that tightly articulated with
16065-491: The southwestern United States, Morocco, India, and western Europe. 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 transporting and accumulating dead individuals in certain areas. Temnospondyls reached a peak diversity during the Early Triassic, and progressively declined throughout
16200-499: 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
16335-493: The stem group, but a few paleontologists opt for more specific terms such as Stegocephali . Limbs evolved prior to terrestrial locomotion , but by the start of the Carboniferous Period, 360 million years ago, a few stem-tetrapods were experimenting with a semiaquatic lifestyle to exploit food and shelter on land. The first crown -tetrapods (those descended from the last common ancestors of extant tetrapods) appeared by
16470-412: 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 , this classification is no longer viable. The basic rhachitomous condition is found in many primitive tetrapods, and
16605-575: The subsequent Middle and Late Triassic, with only members of the Brachyopoidea and Trematosauroidea surviving into the Jurassic and the Cretaceous. Among brachyopoids, the brachyopids Gobiops and Sinobrachyops are known from Middle and late Jurassic deposits across Asia and the chigutisaurid Siderops is known from the Early Jurassic of Australia. The most recent known temnospondyl
16740-521: The term stem-tetrapod to refer to those tetrapod-like vertebrates that are not members of the crown group, including both early limbed "tetrapods" and tetrapodomorph fishes. The term "fishapod" was popularized after the discovery and 2006 publication of Tiktaalik , an advanced tetrapodomorph fish which was closely related to limbed vertebrates and showed many apparently transitional traits. The two subclades of crown tetrapods are Batrachomorpha and Reptiliomorpha . Batrachomorphs are all animals sharing
16875-428: 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
17010-431: The underside of the skull, the pterygoid ; large openings called interpterygoid vacuities are present between the pterygoids; the stapes (a bone involved in hearing) is connected to the parasphenoid and projects upward; the cleithrum , a bone in the pectoral girdle , 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
17145-410: The vertebrae, and osteoderms are also known from a few trematopids. Other temnospondyls, such as Eryops , have been found with small, disc-like bony scutes 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
17280-455: 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 (251.0–245.0 Mya) one group of successful long-snouted fish-eaters, the trematosauroids , even adapted to a life in the sea,
17415-452: 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
17550-1223: Was described by Damiani (2001) under the name Mastodonsauroidea. In their phylogenetic analysis of temnospondyls, Ruta et al. (2007) placed Lydekkerina and its relatives within the clade Rhytidostea , while placing only mastodonsauroid taxa within Capitosauria. Below is a cladogram from Fortuny et al. (2011) showing the phylogenetic relationships of capitosaurs: Lydekkerina huxleyi Rhineceps nyasaensis Uranocentrodon senekalensis Wetlugasaurus angustifrons Odenwaldia heidelbergensis Vladlenosaurus alexeyevi Edingerella madagascariensis Watsonisuchus spp. Xenotosuchus africanus Cherninia denwai Paracyclotosaurus crookshanki Stanocephalosaurus pronus Stanocephalosaurus birdi Procyclotosaurus stantonensis Eocyclotosaurus spp. Quasicyclotosaurus campi Parotosuchus orenburgensis Calmasuchus acri Cyclotosaurus robustus Tatrasuchus wildi Eryosuchus garjainovi Mastodonsaurus giganteus Benthosuchus sushkini Thoosuchus yakovlevi Angusaurus spp. Trematosaurus brauni [REDACTED] [REDACTED] This Temnospondyli -related article
17685-431: 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
17820-537: Was driven primarily by amphibians in the Palaeozoic, dominated by reptiles in the Mesozoic and expanded by the explosive growth of birds and mammals in the Cenozoic. As biodiversity has grown, so has the number of species and the number of niches that tetrapods have occupied. The first tetrapods were aquatic and fed primarily on fish. Today, the Earth supports a great diversity of tetrapods that live in many habitats and subsist on
17955-466: 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
18090-417: Was more subdued during the Permian, but they did begin to fracture into several lineages ancestral to modern reptiles. Amniotes were not the only tetrapods to experiment with prolonged life on land. Some temnospondyls, seymouriamorphs , and diadectomorphs also successfully filled terrestrial niches in the earlier part of the Permian. Non-amniote tetrapods declined in the later part of the Permian. The end of
18225-487: Was the giant chigutisaurid Koolasuchus , known from the Early Cretaceous ( Aptian ) of Australia . It is thought to have survived in rift valleys that were too cold in the winter for crocodylomorphs that normally would have competed with them. Koolasuchus was one of the largest of the brachyopoids, with an estimated weight of 500 kg (1,100 lb). Originally, temnospondyls were classified according to
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