141-403: Cryptobranchoidea Salamandroidea Salamanders are a group of amphibians typically characterized by their lizard -like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten extant salamander families are grouped together under the order Urodela from the group Caudata . Urodela
282-566: A suborder of salamanders found in Asia, European Russia, and the United States. They are known as primitive salamanders , in contrast to Salamandroidea , the advanced salamanders . It has two living subdivisions, Cryptobranchidae ( Asian giant salamanders and hellbenders ), and Hynobiidae , commonly known as Asian salamanders. Giant salamanders are obligate paedomorphs with partial metamorphosis, but Asiatic salamander goes through
423-412: A concealed site in flowing water, and these are usually guarded by an adult, normally the female. Many of the tropical climbing salamanders ( Bolitoglossa ) and lungless salamanders (Plethodontinae) lay a small number of large eggs on land in a well-hidden spot, where they are also guarded by the mother. Some species such as the fire salamanders ( Salamandra ) are ovoviviparous , with the female retaining
564-584: A flash of warning hue on its underside. The red eft, the brightly colored terrestrial juvenile form of the eastern newt ( Notophthalmus viridescens ), is highly poisonous. It is avoided by birds and snakes, and can survive for up to 30 minutes after being swallowed (later being regurgitated). The red salamander ( Pseudotriton ruber ) is a palatable species with a similar coloring to the red eft. Predators that previously fed on it have been shown to avoid it after encountering red efts, an example of Batesian mimicry . Other species exhibit similar mimicry. In California,
705-619: 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,
846-769: A full metamorphosis. The only known exceptions are the Longdong stream salamander , which has been documented as facultatively neotenic, and the Ezo salamander , where a now assumed extinct population from Lake Kuttarush in Hokkaido had neotenic traits like gills in adults. The oldest members of the group are known from the Middle Jurassic ( Bathonian ) aged Yanliao Biota of China. This suborder contains only two families at present. All other members are extinct and are only known as fossils. This salamander article
987-414: A hissing sound, while the sirens sometimes produce quiet clicks, and can resort to faint shrieks if attacked. Similar clicking behaviour was observed in two European newts Lissotriton vulgaris and Ichthyosaura alpestris in their aquatic phase. Vocalization in salamanders has been little studied and the purpose of these sounds is presumed to be the startling of predators. Respiration differs among
1128-437: A lateral row. This may provide an aposematic signal that makes the spines more visible. When the danger has passed, the ribs retract and the skin heals. Although many salamanders have cryptic colors so as to be unnoticeable, others signal their toxicity by their vivid coloring . Yellow, orange, and red are the colors generally used, often with black for greater contrast. Sometimes, the animal postures if attacked, revealing
1269-663: A long body, a laterally flattened tail with dorsal and ventral fins and in some species limb-buds or limbs. Pond-type larvae may have a pair of rod-like balancers on either side of the head, long gill filaments and broad fins. Stream-type larvae are more slender with short gill filaments—in Rhyacotriton and Onychodactylus, and some species in Batrachuperus, the gills and gill rakers are extremely reduced, narrower fins and no balancers, but instead have hind limbs already developed when they hatch. The tadpoles are carnivorous and
1410-638: 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
1551-515: A minute fragment of skin is deadly. In feeding trials, fish, frogs, reptiles, birds, and mammals were all found to be susceptible. Mature adults of some salamander species have "nuptial" glandular tissue in their cloacae , at the base of their tails, on their heads or under their chins. Some females release chemical substances , possibly from the ventral cloacal gland, to attract males, but males do not seem to use pheromones for this purpose. In some plethodonts , males have conspicuous mental glands on
SECTION 10
#17327880835301692-453: 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,
1833-557: 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
1974-606: A reasonable size. Large species such as the Japanese giant salamander ( Andrias japonicus ) eat crabs, fish, small mammals, amphibians, and aquatic insects. In a study of smaller dusky salamanders ( Desmognathus ) in the Appalachian Mountains , their diet includes earthworms , flies , beetles , beetle larvae, leafhoppers , springtails , moths , spiders , grasshoppers , and mites . Cannibalism sometimes takes place, especially when resources are short or time
2115-488: 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
2256-400: 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
2397-432: A second. In some species, the tongue is attached anteriorly to the floor of the mouth, while in others, it is mounted on a pedicel. It is rendered sticky by secretions of mucus from glands in its tip and on the roof of the mouth. High-speed cinematography shows how the tiger salamander ( Ambystoma tigrinum ) positions itself with its snout close to its prey. Its mouth then gapes widely, the lower jaw remains stationary, and
2538-401: 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
2679-677: A short period of time and involves the closing of the gill slits and the loss of structures such as gills and tail fins that are not required as adults. At the same time, eyelids develop, the mouth becomes wider, a tongue appears, and teeth are formed. The aqueous larva emerges onto land as a terrestrial adult. Not all species of salamanders follow this path. Neoteny , also known as paedomorphosis, has been observed in all salamander families, and may be universally possible in all salamander species. In this state, an individual may retain gills or other juvenile features while attaining reproductive maturity. The changes that take place at metamorphosis are under
2820-513: A simplified retinal structure, and in cave dwellers such as the Georgia blind salamander , they are absent or covered with a layer of skin. In amphibious species, the eyes are a compromise and are nearsighted in air and farsighted in water. Fully terrestrial species such as the fire salamander have a flatter lens which can focus over a much wider range of distances. To find their prey, salamanders use trichromatic color vision extending into
2961-497: 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
SECTION 20
#17327880835303102-407: A small lizard, having a basal tetrapod body form with a cylindrical trunk, four limbs, and a long tail. Except in the family Salamandridae, the head, body, and tail have a number of vertical depressions in the surface which run from the mid-dorsal region to the ventral area and are known as costal grooves . Their function seems to be to help keep the skin moist by channeling water over the surface of
3243-452: 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
3384-449: 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
3525-475: 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,
3666-621: 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
3807-575: 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
3948-402: Is a stub . You can help Misplaced Pages by expanding it . Tetrapod A tetrapod ( / ˈ t ɛ t r ə ˌ p ɒ d / ; from Ancient Greek τετρα- (tetra-) 'four' and πούς (poús) 'foot') 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
4089-946: Is a scientific Latin term based on the Ancient Greek οὐρά δήλη : ourà dēlē "conspicuous tail". Caudata is the Latin for "tailed ones", from cauda : "tail". Salamander diversity is highest in eastern North America , especially in the Appalachian Mountains ; most species are found in the Holarctic realm , with some species present in the Neotropical realm . Salamanders never have more than four toes on their front legs and five on their rear legs, but some species have fewer digits and others lack hind limbs. Their permeable skin usually makes them reliant on habitats in or near water or other cool, damp places. Some salamander species are fully aquatic throughout their lives, some take to
4230-518: Is advanced into the salamander's mouth, the teeth tips relax and bend in the same direction, encouraging movement toward the throat, and resisting the prey's escape. Many salamanders have patches of teeth attached to the vomer and the palatine bones in the roof of the mouth, and these help to retain prey. All types of teeth are resorbed and replaced at intervals throughout the animal's life. A terrestrial salamander catches its prey by flicking out its sticky tongue in an action that takes less than half
4371-410: 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
Salamander - Misplaced Pages Continue
4512-563: Is another large, long-lived species with dwindling numbers and fewer juveniles reaching maturity than previously. Another alarming finding is the increase in abnormalities in up to 90% of the hellbender population in the Spring River watershed in Arkansas. Habitat loss, silting of streams, pollution and disease have all been implicated in the decline and a captive breeding programme at Saint Louis Zoo has been successfully established. Of
4653-479: Is being undertaken to assess the status of these salamanders, and to better understand the factors involved in their population declines, with a view to taking action. Ambystoma mexicanum , an aquatic salamander, is a species protected under the Mexican UMA (Unit for Management and conservation of wildlife) as of April 1994. Another detrimental factor is that the axolotl lost their role as a top predator since
4794-637: Is internal. As a general rule, salamanders with internal fertilization have indirect sperm transfer, but in species like the Sardinian brook salamander , the Corsican brook salamander , the Caucasian salamander and the Pyrenean brook salamander , the male transfer his sperm directly into the female cloaca. For the species with indirect sperm transfer, the male deposits a spermatophore on the ground or in
4935-416: Is larger than that of the female, is used during the amplexus embrace to propel the mating couple to a secluded location. In terrestrial species, the tail moves to counterbalance the animal as it runs, while in the arboreal salamander and other tree-climbing species, it is prehensile . The tail is also used by certain plethodontid salamanders that can jump, to help launch themselves into the air. The tail
5076-433: Is limited. Tiger salamander tadpoles in ephemeral pools sometimes resort to eating each other, and are seemingly able to target unrelated individuals. Adult blackbelly salamanders ( Desmognathus quadramaculatus ) prey on adults and young of other species of salamanders, while their larvae sometimes cannibalise smaller larvae. Most species of salamander have small teeth in both their upper and lower jaws. Unlike frogs , even
5217-464: Is not just limited to limbs but extends to vital organs such as the heart, jaw, and parts of the spinal cord, showing their uniqueness compared to different types of vertebrates. This ability is most remarkable for occurring without any type of scarring. This has made salamanders an invaluable model organism in scientific research aimed at understanding and achieving regenerative processes for medical advancements in human and animal biology. Members of
5358-454: Is restricted to the slightly cooler and wetter conditions in north-facing cove forests in the southern Appalachians, and to higher elevations above 900 m (3,000 ft), while the former is more adaptable, and would be perfectly able to inhabit these locations, but some unknown factor seems to prevent the two species from co-existing. One species, the Anderson's salamander , is one of
5499-465: 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
5640-477: 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
5781-402: 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
Salamander - Misplaced Pages Continue
5922-412: Is used in courtship and as a storage organ for proteins and lipids. It also functions as a defense against predation, when it may be lashed at the attacker or autotomised when grabbed. Unlike frogs, an adult salamander is able to regenerate limbs and its tail when these are lost. The skin of salamanders, in common with other amphibians, is thin, permeable to water, serves as a respiratory membrane, and
6063-407: Is well-supplied with glands. It has highly cornified outer layers, renewed periodically through a skin shedding process controlled by hormones from the pituitary and thyroid glands. During moulting, the skin initially breaks around the mouth, and the animal moves forward through the gap to shed the skin. When the front limbs have been worked clear, a series of body ripples pushes the skin toward
6204-703: The Alaska Panhandle . They had an exclusively Laurasian distribution until Bolitoglossa invaded South America from Central America, probably by the start of the Early Miocene , about 23 million years ago. They also lived on the Caribbean Islands during the early Miocene epoch, confirmed by the discovery of Palaeoplethodon hispaniolae , found trapped in amber in the Dominican Republic . Vertebrae fossils recovered from
6345-526: 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
6486-942: The Holarctic and Neotropical regions, not reaching south of the Mediterranean Basin , the Himalayas , or in South America the Amazon Basin . They do not extend north of the Arctic tree line , with the northernmost Asian species, Salamandrella keyserlingii , which can survive long-term freezing at −55 °C, occurring in the Siberian larch forests of Sakha and the most northerly species in North America, Ambystoma laterale , reaching no farther north than Labrador and Taricha granulosa not beyond
6627-652: 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
6768-405: 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
6909-615: The Murgon fossil site have been tentatively attributed to that of a Salamander, though its true identity is disputed. If the vertebrae truly belong to a Salamander, they would represent the only Salamanders in Australia . There are about 760 living species of salamander. One-third of the known salamander species are found in North America. The highest concentration of these is found in the Appalachian Mountains region, where
7050-465: 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
7191-1166: 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 ;
SECTION 50
#17327880835307332-448: The amphiumas , metamorphosis is incomplete, and they retain one pair of gill slits as adults, with fully functioning internal lungs. Some species that lack lungs respire through gills. In most cases, these are external gills, visible as tufts on either side of the head. Some terrestrial salamanders have lungs used in respiration, although these are simple and sac-like, unlike the more complex organs found in mammals . Many species, such as
7473-399: The cloud forests of Guatemala and Mexico during the 1970s were found by 2009 to be rare. Few data have been gathered on population sizes over the years and, by intensive surveying of historic and suitable new locations, it has been possible to locate individuals of other species, such as Parvimolge townsendi , which had been thought to be extinct . Currently, the major lines of defense for
7614-495: The family Salamandridae are mostly known as newts and lack the costal grooves along the sides of their bodies typical of other groups. The skin of some species contains the powerful poison tetrodotoxin ; these salamanders tend to be slow-moving and have bright warning coloration to advertise their toxicity. Salamanders typically lay eggs in water and have aquatic larvae, but great variation occurs in their lifecycles . Some species in harsh environments reproduce while still in
7755-593: The lens or retina of the eye. Within only a few weeks of losing a piece of a limb, a salamander perfectly reforms the missing structure. Salamanders split off from the other amphibians during the mid- to late Permian, and initially were similar to modern members of the Cryptobranchoidea . Their resemblance to lizards is the result of symplesiomorphy , their common retention of the primitive tetrapod body plan, but they are no more closely related to lizards than they are to mammals. Their nearest relatives are
7896-635: The olm , have both lungs and gills as adults. In the Necturus , external gills begin to form as a means of combating hypoxia in the egg as egg yolk is converted into metabolically active tissue. Molecular changes in the mudpuppy during post-embryonic development primarily due to the thyroid gland prevent the internalization of the external gills as seen in most salamanders that undergo metamorphosis. The external gills seen in salamanders differs greatly from that of amphibians with internalized gills. Unlike amphibians with internalized gills which typically rely on
8037-415: 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
8178-498: The ultraviolet range, based on three photoreceptor types that are maximally sensitive around 450, 500, and 570 nm. The larvae, and the adults of some highly aquatic species, also have a lateral line organ, similar to that of fish, which can detect changes in water pressure. All salamanders lack middle ear cavity, eardrum and eustachian tube , but have an opercularis system like frogs, and are still able to detect airborne sound. The opercularis system consists of two ossicles:
8319-605: 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
8460-468: The 20 species of minute salamanders ( Thorius spp.) in Mexico, half are believed to have become extinct and most of the others are critically endangered. Specific reasons for the decline may include climate change, chytridiomycosis, or volcanic activity, but the main threat is habitat destruction as logging, agricultural activities, and human settlement reduce their often tiny, fragmented ranges. Survey work
8601-499: The California newt has many large poison glands in its skin, is diurnal, and is avoided by snakes. Some salamander species use tail autotomy to escape predators. The tail drops off and wriggles around for a while after an attack, and the salamander either runs away or stays still enough not to be noticed while the predator is distracted. The tail regrows with time, and salamanders routinely regenerate other complex tissues, including
SECTION 60
#17327880835308742-632: 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
8883-507: 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
9024-689: 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
9165-517: The Plethodontidae are thought to have originated in mountain streams. Here, vegetation zones and proximity to water are of greater importance than altitude. Only species that adopted a more terrestrial mode of life have been able to disperse to other localities. The northern slimy salamander ( Plethodon glutinosus ) has a wide range and occupies a habitat similar to that of the southern gray-cheeked salamander ( Plethodon metcalfi ). The latter
9306-403: The animal of an approaching predator. Salamanders are usually considered to have no voice and do not use sound for communication in the way that frogs do. Before mating, they communicate by pheromone signaling; some species make quiet ticking, clicking, squeaks or popping noises, perhaps by the opening and closing of valves in the nose. Most salamanders lack vocal cords, but a larynx is present in
9447-421: The animal slippery and more difficult for predators to catch. Granular glands scattered on the upper surface, particularly the head, back, and tail, produce repellent or toxic secretions. Some salamander toxins are particularly potent. The rough-skinned newt ( Taricha granulosa ) produces the neurotoxin tetrodotoxin , the most toxic nonprotein substance known. Handling the newts does no harm, but ingestion of even
9588-441: 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
9729-403: The axolotl does not account for the overall lack of diversity. Evidence points toward a historical bottlenecking of Ambystoma that contributes to the variation issues and no longer a large genetic pool for it to pull from, thus raising concern for inbreeding due to lack of gene flow. One way researchers are looking into maintaining genetic diversity within the population is via cryopreservation of
9870-506: 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,
10011-507: 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
10152-482: 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
10293-517: 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
10434-401: The body. Some aquatic species, such as sirens and amphiumas , have reduced or absent hind limbs, giving them an eel -like appearance, but in most species, the front and rear limbs are about the same length and project sideward, barely raising the trunk off the ground. The feet are broad with short digits, usually four on the front feet and five on the rear. Salamanders do not have claws, and
10575-477: The breeding season. Cave species dwelling in darkness lack pigmentation and have a translucent pink or pearlescent appearance. Salamanders range in size from the minute salamanders , with a total length of 27 mm ( 1 + 1 ⁄ 8 in), including the tail, to the Chinese giant salamander which reaches 1.8 m (6 ft) and weighs up to 65 kg (145 lb). All the largest species are found in
10716-453: The changing of pressures within the buccal and pharyngeal cavities to ensure diffusion of oxygen onto the gill curtain, neotenic salamanders such as Necturus use specified musculature, such as the levatores arcuum, to move external gills to keep the respiratory surfaces constantly in contact with new oxygenated water. Salamanders are opportunistic predators . They are generally not restricted to specific foods, but feed on almost any organism of
10857-629: 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
10998-455: The chin which are pressed against the females' nostrils during the courtship ritual. They may function to speed up the mating process, reducing the risk of its being disrupted by a predator or rival male. The gland at the base of the tail in Plethodon cinereus is used to mark fecal pellets to proclaim territorial ownership. Olfaction in salamanders plays a role in territory maintenance,
11139-469: The cloacae of females. The results of this research may be used in captive-breeding programmes for endangered species. The order name Urodela comes from the name Urodèles given by André Marie Constant Duméril in 1805, it is derived from the Greek words οὐρά ourā́ "tail" and δῆλος dēlos "visible, conspicuous" because of their "persistent" tails. Disagreement exists among different authorities as to
11280-423: The columella (equivalent to the stapes of higher vertebrates ) which is fused to the skull, and the operculum. An opercularis muscle connects the latter to the pectoral girdle, and is kept under tension when the animal is alert. The system seems able to detect low-frequency vibrations (500–600 Hz), which may be picked up from the ground by the fore limbs and transmitted to the inner ear. These may serve to warn
11421-616: The conservation of Salamanders includes both in situ and ex situ conservation methods. There are efforts in place for certain members of the Salamander family to be conserved under a conservation breeding program (CBP) but there should be research done ahead of time to determine if the Salamander species is actually going to value from the CBP, as researchers have noted that some species of amphibians completely fail in this environment. Various conservation initiatives are being attempted around
11562-497: The control of thyroid hormones and in obligate neotenes such as the axolotl ( Ambystoma mexicanum ), the tissues are seemingly unresponsive to the hormones. In other species, the changes may not be triggered because of underactivity of the hypothalamus-pituitary-thyroid mechanism which may occur when conditions in the terrestrial environment are too inhospitable. This may be due to cold or wildly fluctuating temperatures, aridity, lack of food, lack of cover, or insufficient iodine for
11703-509: The definition of the terms Caudata and Urodela. Some maintain that the Urodela should be restricted to the crown group , with the Caudata being used for the total group. Others restrict the name Caudata to the crown group and use Urodela for the total group. The former approach seems to be most widely adopted and is used in this article. Cryptobranchoidea The Cryptobranchoidea are
11844-603: The different species of salamanders, and can involve gills, lungs, skin, and the membranes of mouth and throat. Larval salamanders breathe primarily by means of gills , which are usually external and feathery in appearance. Water is drawn in through the mouth and flows out through the gill slits. Some neotenic species such as the mudpuppy ( Necturus maculosus ) retain their gills throughout their lives, but most species lose them at metamorphosis . The embryos of some terrestrial lungless salamanders, such as Ensatina , that undergo direct development, have large gills that lie close to
11985-527: 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
12126-405: 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
12267-428: 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
12408-730: 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
12549-405: The egg's surface. When present in adult salamanders, lungs vary greatly among different species in size and structure. In aquatic, cold-water species like the torrent salamanders ( Rhyacotriton ), the lungs are very small with smooth walls, while species living in warm water with little dissolved oxygen, such as the lesser siren ( Siren intermedia ), have large lungs with convoluted surfaces. In
12690-753: The eggs are laid. In the Asiatic salamanders , the giant salamanders and Sirenidae , which are the most primitive groups, the fertilization is external. In a reproductive process similar to that of typical frogs, the male releases sperm onto the egg mass. These salamanders also have males that exhibit parental care , which otherwise only occur in females with internal fertilization. Three different types of egg deposition occur. Ambystoma and Taricha spp. spawn large numbers of small eggs in quiet ponds where many large predators are unlikely. Most dusky salamanders ( Desmognathus ) and Pacific giant salamanders ( Dicamptodon ) lay smaller batches of medium-sized eggs in
12831-436: The eggs inside her body until they hatch, either into larvae to be deposited in a water body, or into fully formed juveniles. In temperate regions, reproduction is usually seasonal and salamanders may migrate to breeding grounds. Males usually arrive first and in some instances set up territories . Typically, a larval stage follows in which the organism is fully aquatic. The tadpole has three pairs of external gills, no eyelids,
12972-584: 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
13113-528: The few species of living amphibians to occur in brackish or salt water. Many salamanders do not use vocalisations, and in most species the sexes look alike, so they use olfactory and tactile cues to identify potential mates, and sexual selection occurs. Pheromones play an important part in the process and may be produced by the abdominal gland in males and by the cloacal glands and skin in both sexes. Males are sometimes to be seen investigating potential mates with their snouts. In Old World newts, Triturus spp.,
13254-446: 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
13395-489: 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
13536-481: The formation of thyroid hormones. Genetics may also play a part. The larvae of tiger salamanders ( Ambystoma tigrinum ), for example, develop limbs soon after hatching and in seasonal pools promptly undergo metamorphosis. Other larvae, especially in permanent pools and warmer climates, may not undergo metamorphosis until fully adult in size. Other populations in colder climates may not metamorphose at all, and become sexually mature while in their larval forms. Neoteny allows
13677-402: The four families giant salamanders , sirens , Congo eels and Proteidae , who are all aquatic and obligate paedomorphs. Some of the largest terrestrial salamanders, which goes through full metamorphosis, belongs to the family of Pacific giant salamanders , and are much smaller. Most salamanders are between 10 and 20 cm (4 and 8 in) in length. An adult salamander generally resembles
13818-642: The frogs and toads, within Batrachia . The oldest known total-group ( Caudata ) salamander is Triassurus from the Triassic of Kyrgyzstan . Further salamander fossils are known from the Middle Jurassic of England , Scotland , China , and Kazakhstan . The oldest known crown-group salamander ( Urodela ) remains uncertain but recent analyses suggest it is Valdotriton from the Late Jurassic of Spain . Salamanders are found only in
13959-447: The future. Skin secretions of the tiger salamander ( Ambystoma tigrinum ) fed to rats have been shown to produce aversion to the flavor, and the rats avoided the presentational medium when it was offered to them again. The fire salamander ( Salamandra salamandra ) has a ridge of large granular glands down its spine which are able to squirt a fine jet of toxic fluid at its attacker. By angling its body appropriately, it can accurately direct
14100-491: 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,
14241-419: 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
14382-416: The introduction of locally exotic species such as Nile tilapia and carp. Tilapia and carp directly compete with axolotls by consuming their eggs, larvae, and juveniles. Climate change has also immensely affected axolotls and their populations throughout the southern Mexico area. Due to its proximity to Mexico City , officials are currently working on programs at Lake Xochimilco to bring in tourism and educate
14523-408: 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 ,
14664-402: The larvae of salamanders possess these teeth. Although larval teeth are shaped like pointed cones, the teeth of adults are adapted to enable them to readily grasp prey. The crown , which has two cusps (bicuspid), is attached to a pedicel by collagenous fibers. The joint formed between the bicuspid and the pedicel is partially flexible, as it can bend inward, but not outward. When struggling prey
14805-403: The larval stage may last from days to years, depending on species. Sometimes this stage is completely bypassed, and the eggs of most lungless salamanders (Plethodontidae) develop directly into miniature versions of the adult without an intervening larval stage. By the end of the larval stage, the tadpoles already have limbs and metamorphosis takes place normally. In salamanders, this occurs over
14946-617: The larval state. The word salamander comes from Old French salamandre from Latin salamandra from Greek σαλαμάνδρα : salamándra, of uncertain, possibly, pre-Greek origin. The Greek word is used for the fire salamander . The skin lacks scales and is moist and smooth to the touch, except in newts of the Salamandridae, which may have velvety or warty skin, wet to the touch. The skin may be drab or brightly colored, exhibiting various patterns of stripes, bars, spots, blotches, or dots. Male newts become dramatically colored during
15087-827: The last few decades of the 20th century, although no direct link between the fungus and the population decline has yet been found. The IUCN made further efforts in 2005 as they established the Amphibian Conservation Action Plan (ACAP), which was subsequently followed by Amphibian Ark (AArk), Amphibian Specialist Group (ASG), and finally the umbrella organization known as the Amphibian Survival Alliance (ASA). Researchers also cite deforestation , resulting in fragmentation of suitable habitats, and climate change as possible contributory factors. Species such as Pseudoeurycea brunnata and Pseudoeurycea goebeli that had been abundant in
15228-511: 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
15369-579: 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
15510-736: The local population on the restoration of the natural habitat of these creatures. This proximity is a large factor that has impacted the survival of the axolotl, as the city has expanded to take over the Xochimilco region in order to make use of its resources for water and provision and sewage. It is farmed for use in research facilities and so may one day return to its natural habitat. The recent decline in population has substantially impacted genetic diversity among populations, making it difficult to further progress scientifically. Some genetic indiversity due to paedeomorphism in Ambystoma species such as
15651-407: The lungless salamanders ( family Plethodontidae and the clawed salamanders in the family of Asiatic salamanders ), no lungs or gills are present, and gas exchange mostly takes place through the skin, known as cutaneous respiration , supplemented by the tissues lining the mouth. To facilitate this, these salamanders have a dense network of blood vessels just under the skin and in the mouth. In
15792-468: The males are sexually dimorphic and display in front of the females. Visual cues are also thought to be important in some Plethodont species. Except for terrestrial species in the three families Plethodontidae , Ambystomatidae , and Salamandridae , salamanders mate in water. The mating varies from courtship between a single male and female to explosive group breeding. In the clade Salamandroidea , which makes up about 90% of all species, fertilization
15933-514: The mudpuppy (Necturus) and some other species, and the Pacific giant salamanders and a few others have a large larynx and bands known as plicae vocales. The California giant salamander can produce a bark or rattle, and a few species can squeak by contracting muscles in the throat. The arboreal salamander can squeak using a different mechanism; it retracts its eyes into its head, forcing air out of its mouth. The ensatina salamander occasionally makes
16074-412: 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
16215-408: 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 ,
16356-802: 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
16497-407: 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
16638-542: The palatable yellow-eyed salamander ( Ensatina eschscholtzii ) closely resembles the toxic California newt ( Taricha torosa ) and the rough-skinned newt ( Taricha granulosa ), whereas in other parts of its range, it is cryptically colored. A correlation exists between the toxicity of Californian salamander species and diurnal habits: relatively harmless species like the California slender salamander ( Batrachoseps attenuatus ) are nocturnal and are eaten by snakes, while
16779-454: 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
16920-577: The prey, which is then swallowed. Though frequently feeding on slow-moving animals like snails , shrimps and worms , sirenids are unique among salamanders for having developed herbivory speciations, such as beak-like jaw ends and extensive intestines. They feed on algae and other soft-plants in the wild, and easily eat offered lettuce . Salamanders have thin skins and soft bodies, move rather slowly and might appear vulnerable to opportunistic predation, but have several effective lines of defense. Mucus coating on damp skin makes them difficult to grasp, and
17061-486: The rear. The hind limbs are extracted and push the skin farther back, before it is eventually freed by friction as the salamander moves forward with the tail pressed against the ground. The animal often then eats the resulting sloughed skin. Glands in the skin discharge mucus which keeps the skin moist, an important factor in skin respiration and thermoregulation. The sticky layer helps protect against bacterial infections and molds, reduces friction when swimming, and makes
17202-410: The recognition of predators, and courtship rituals, but is probably secondary to sight during prey selection and feeding. Salamanders have two types of sensory areas that respond to the chemistry of the environment. Olfactory epithelium in the nasal cavity picks up airborne and aquatic odors, while adjoining vomeronasal organs detect nonvolatile chemical cues, such as tastes in the mouth. In plethodonts,
17343-430: 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
17484-477: The salamander family. Research is being done on the environmental cues that have to be replicated before captive animals can be persuaded to breed. Common species such as the tiger salamander and the mudpuppy are being given hormones to stimulate the production of sperm and eggs, and the role of arginine vasotocin in courtship behaviour is being investigated. Another line of research is artificial insemination , either in vitro or by inserting spermatophores into
17625-447: The sensory epithelium of the vomeronasal organs extends to the nasolabial grooves , which stretch from the nostrils to the corners of the mouth. These extended areas seem to be associated with the identification of prey items, the recognition of conspecifics , and the identification of individuals. The eyes of most salamanders are adapted primarily for vision at night. In some permanently aquatic species, they are reduced in size and have
17766-462: The shape of the foot varies according to the animal's habitat. Climbing species have elongated, square-tipped toes, while rock-dwellers have larger feet with short, blunt toes. The tree-climbing salamander ( Bolitoglossa sp.) has plate-like webbed feet which adhere to smooth surfaces by suction, while the rock-climbing Hydromantes species from California have feet with fleshy webs and short digits and use their tails as an extra limb. When ascending,
17907-429: The slimy coating may have an offensive taste or be toxic. When attacked by a predator, a salamander may position itself to make the main poison glands face the aggressor. Often, these are on the tail, which may be waggled or turned up and arched over the animal's back. The sacrifice of the tail may be a worthwhile strategy, if the salamander escapes with its life and the predator learns to avoid that species of salamander in
18048-457: The species to survive even when the terrestrial environment is too harsh for the adults to thrive on land. A general decline in living amphibian species has been linked with the fungal disease chytridiomycosis . A higher proportion of salamander species than of frogs or caecilians are in one of the at-risk categories established by the IUCN . Salamanders showed a significant diminution in numbers in
18189-432: The spermatophores from the male axolotl. It is a safe and non-invasive method that requires the collection of the spermatophores and places them into a deep freeze for preservation. Most importantly, they have found that there is only limited damage done to the spermatophores upon thawing and thus it is a viable option. As of 2013, it is a method that is being used to save not only the axolotl but also numerous other members of
18330-438: The spray for a distance of up to 80 cm (30 in). The Iberian ribbed newt ( Pleurodeles waltl ) has another method of deterring aggressors. Its skin exudes a poisonous, viscous fluid and at the same time, the newt rotates its sharply pointed ribs through an angle between 27 and 92°, and adopts an inflated posture. This action causes the ribs to puncture the body wall, each rib protruding through an orange wart arranged in
18471-502: 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
18612-405: The tail props up the rear of the body, while one hind foot moves forward and then swings to the other side to provide support as the other hind foot advances. In larvae and aquatic salamanders, the tail is laterally flattened, has dorsal and ventral fins, and undulates from side to side to propel the animal through the water. In the families Ambystomatidae and Salamandridae, the male's tail, which
18753-521: 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
18894-410: The throat, assisted by depression of the eyeballs into the roof of the mouth. Many lungless salamanders of the family Plethodontidae have more elaborate feeding methods. Muscles surrounding the hyoid bone contract to store elastic energy in springy connective tissue, and actually "shoot" the hyoid bone out of the mouth, thus elongating the tongue. Muscles that originate in the pelvic region and insert in
19035-430: The tongue are used to reel the tongue and the hyoid back to their original positions. An aquatic salamander lacks muscles in the tongue, and captures its prey in an entirely different manner. It grabs the food item, grasps it with its teeth, and adopts a kind of inertial feeding. This involves tossing its head about, drawing water sharply in and out of its mouth, and snapping its jaws, all of which tend to tear and macerate
19176-487: The tongue bulges and changes shape as it shoots forward. The protruded tongue has a central depression, and the rim of this collapses inward as the target is struck, trapping the prey in a mucus-laden trough. Here it is held while the animal's neck is flexed, the tongue retracted and jaws closed. Large or resistant prey is retained by the teeth while repeated protrusions and retractions of the tongue draw it in. Swallowing involves alternate contraction and relaxation of muscles in
19317-420: The water according to species, and the female picks this up with her vent. The spermatophore has a packet of sperm supported on a conical gelatinous base, and often an elaborate courtship behavior is involved in its deposition and collection. Once inside the cloaca, the spermatozoa move to the spermatheca , one or more chambers in the roof of the cloaca, where they are stored for sometimes lengthy periods until
19458-454: The water intermittently, and others are entirely terrestrial as adults. This group of amphibians is capable of regenerating lost limbs as well as other damaged parts of their bodies. Researchers hope to reverse engineer the regenerative processes for potential human medical applications, such as brain and spinal cord injury treatment or preventing harmful scarring during heart surgery recovery. The remarkable ability of salamanders to regenerate
19599-480: The world. The Chinese giant salamander , at 1.8 m (6 ft) the largest amphibian in the world, is critically endangered , as it is collected for food and for use in traditional Chinese medicine . An environmental education programme is being undertaken to encourage sustainable management of wild populations in the Qinling Mountains and captive breeding programmes have been set up. The hellbender
19740-547: 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
19881-417: 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
#529470