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68-512: See text . Chroniosuchia is a group of tetrapods that lived from the Middle Permian to Late Triassic in what is now Eastern Europe , Kyrgyzstan , China and Germany . Chroniosuchians are often thought to be reptiliomorphs , but some recent phylogenetic analyses suggest instead that they are stem-tetrapods . They were all rather short limbed with a strong tail and elongated snout, somewhat resembling modern crocodiles . The group

136-823: A pleurocentrum and an intercentrum on the bottom, and a neural arch on top. Chroniosuchians have shizomerous vertebrae, meaning that the pleurocentrum makes up most of the body of the vertebra while the intercentrum is small and wedge-like. Below is the cladogram showing the preferred phylogeny of Buchwitz et al. (2012): Madygenerpeton Chroniosaurus dongusensis Chroniosaurus levis Suchonica Jarilinus Chroniosuchus Uralerpeton Synesuchus Bystrowiella Bystrowiana Axitectum Dromotectum [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Tetrapod A tetrapod ( / ˈ t ɛ t r ə ˌ p ɒ d / ; from Ancient Greek τετρα- (tetra-) 'four' and πούς (poús) 'foot')

204-411: A primate with traits that would represent anything in between humans and the other great apes . If the concept of an ape-man were based on neontology, then our phenotype would resemble Bigfoot . Since the concept was based on paleontology, the idea of an ape-man could possibly be represented by the fossil hominids. Neontology studies extant (living) taxa and recently extinct taxa, but declaring

272-619: 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,

340-638: 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

408-453: 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,

476-557: 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

544-410: A pair of "anterior wings" that slip into a notch in the posterior margin of the osteoderm in front of it. Chroniosuchians are distinguished from other early reptiliomorphs by the lack of intertemporal bones in the skull, as well as the presence of holes in front of the eye sockets called antorbital fenestrae . Like many early tetrapods, chroniosuchians have vertebrae that are divided into three parts:

612-488: 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

680-400: 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

748-401: 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

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816-497: 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

884-452: 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

952-449: 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

1020-536: A taxon to be definitively extinct is difficult. Taxa that have previously been declared extinct may reappear over time. Species that were once considered extinct and then reappear unscathed are characterized by the term "the Lazarus effect", or are also called a Lazarus species . For example, a study determined that 36% of supposed mammalian extinction had been proven, while the other 64% had insufficient evidence to be declared extinct or had been rediscovered. Currently,

1088-475: 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,

1156-621: 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

1224-575: 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

1292-410: 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

1360-708: 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

1428-399: Is broadly agreed or certified that no members of the group are still alive. Conversely, an extinct taxon can be reclassified as extant if there are new discoveries of living species (" Lazarus species "), or if previously known extant species are reclassified as members of the taxon. Most biologists, zoologists , and botanists are in practice neontologists, and the term neontologist

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1496-465: 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

1564-477: 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

1632-402: 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

1700-509: Is traditionally considered to be a suborder or order of labyrinthodonts . Chroniosuchians likely had ecological niches as riverside predators, and may have been outcompeted by semiaquatic true reptiles such as phytosaurs in the late Triassic . Most forms bore a heavy armour of scutes along the back, possibly for protection against land born predators like therapsids , or to strengthen the axial skeleton for terrestrial locomotion. Indeed, femoral microanatomy of Chroniosaurus suggests that it

1768-443: Is used largely by paleontologists referring to non- paleontologists . Stephen Jay Gould said of neontology: All professions maintain their parochialisms , and I trust that nonpaleontological readers will forgive our major manifestation . We are paleontologists, so we need a name to contrast ourselves with all you folks who study modern organisms in human or ecological time . You therefore become neontologists. We do recognize

1836-526: 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

1904-570: The International Union for Conservation of Nature considers a taxon to be recently extinct if the extinction occurred after 1500 C.E. A recently considered extinct mammal was the Bouvier's red colobus monkey, who was considered extinct up until 2015 when it was rediscovered after 40 years with no recorded sightings. Neontology's fundamental theories rely on biological models of natural selection and speciation that connect genes,

1972-652: 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

2040-405: 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

2108-465: 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

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2176-1166: 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 ;

2244-415: 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

2312-605: 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

2380-632: 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

2448-507: 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

2516-689: 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

2584-441: 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

2652-506: 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,

2720-507: 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

2788-482: 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

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2856-517: 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

2924-629: 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

2992-527: 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

3060-405: 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

3128-428: 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

3196-730: 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

3264-584: 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

3332-446: 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

3400-489: 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

3468-491: 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,

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3536-419: 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

3604-408: 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 ,

3672-579: 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

3740-412: 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

3808-408: 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 ,

3876-802: 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

3944-407: 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

4012-503: The population structure than paleontology does. When the scientific community accepted the synthetic theory of evolution , taxonomies became phylogenetic . As a result, information gaps arose within the fossil record of species, especially in Homo sapiens . The anthropologists who accepted the synthetic theory reject the idea of an "ape-man" because the concept had mistaken paleontology with neontology. An ape-man, in actuality, would be

4080-454: 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

4148-430: 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

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4216-502: 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

4284-521: 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

4352-450: The tetrapod crown group. The cladogram below illustrates the relationships of stem-tetrapods. All these lineages are extinct except for Dipnomorpha and Tetrapoda; from Swartz, 2012: Dipnomorpha (lungfishes and relatives) [REDACTED] Kenichthys Rhizodontidae [REDACTED] Marsdenichthys Canowindra Koharalepis Neontology#Extant taxa versus extinct taxa A taxon can be classified as extinct if it

4420-725: The unbalanced and parochial nature of this dichotomous division. Neontological evolutionary biology has a temporal perspective between 100 and 1000 years. Neontology's fundamental basis relies on models of natural selection as well as speciation . Neontology's methods, when compared to evolutionary paleontology , have a greater emphasis on experiments. There are more frequent discontinuities present in paleontology than in neontology, because paleontology involves extinct taxa. Neontology has organisms actually present and available to sample and perform research on. Neontology's research method uses cladistics to examine morphologies and genetics . Neontology data has more emphasis on genetic data and

4488-464: Was amphibious to terrestrial. The most distinguishing features of chroniosuchians are the rows of interlocking bony plates called osteoderms that run along their backs from head to tail. They are the most commonly found remains of chroniosuchians. Each osteoderm is paired with a single vertebra. The osteoderms are flat plates connected to the neural arches of vertebra by an extension of bone on their undersurfaces. The front margin of each osteoderm has

4556-547: 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

4624-417: 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

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