Salamander

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For the mythical lizard, see Cultural depictions of salamanders.
For other uses, see Salamander (disambiguation).

Salamanders
Temporal range:
Ma
Spotted salamander, Ambystoma maculatum
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Clade: Caudata
Order: Urodela
Duméril, 1806
Suborders

Cryptobranchoidea
Salamandroidea

Native distribution of salamanders (in green)

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.[2] 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,[3] 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 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.[4] The remarkable ability of salamanders to regenerate 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 very remarkable for occurring without any type of scarring. ⁤⁤This has made salamanders an invaluable model organisms in scientific research aimed at understanding and achieving regenerative processes for medical advancements in human and animal biology.[5]

Members of 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 the larval state.

Etymology

The word salamander comes from Old French salamandre from Latin salamandra from Greek σαλαμάνδρα,[6] which is used for the fire salamander.[7]

Description

X-ray image of 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 the breeding season. Cave species dwelling in darkness lack pigmentation and have a translucent pink or pearlescent appearance.[8]

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 both aquatic and paedomorphic.[9] Some of the largest terrestrial salamanders, which goes through full metamorphosis, are found in the family of Pacific giant salamanders, and are much smaller.[10] Most salamanders, however, are between 10 and 20 cm (4 and 8 in) in length.[11]

Trunk, limbs and tail

An adult salamander generally resembles a small lizard, having a basal

costal grooves. Their function seems to be to help keep the skin moist by channeling water over the surface of the body.[12]

Sirens have an eel-like appearance.

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 sidewards, 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 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, 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.[13]

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

plethodontid salamanders that can jump, to help launch themselves into the air.[13] The tail 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.[13]

Skin

Rough-skinned newt

The skin of salamanders, in common with other amphibians, is thin, permeable to water, serves as a respiratory membrane, and is well-supplied with glands. It has highly

pituitary and thyroid glands. During moulting, the skin initially breaks around the mouth, and the animal moves forwards through the gap to shed the skin. When the front limbs have been worked clear, a series of body ripples pushes the skin towards 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.[14] The animal often then eats the resulting sloughed skin.[8]

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 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.[14] 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 a minute fragment of skin is deadly. In feeding trials, fish, frogs, reptiles, birds, and mammals were all found to be susceptible.[15]

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

Plethodon cinereus is used to mark fecal pellets to proclaim territorial ownership.[16]

Senses

The front part of the olm's head carries sensitive chemo-, mechano-, and electroreceptors.
Biofluorescence
can be observed across various salamander species

conspecifics, and the identification of individuals.[18]

The eyes of most salamanders are adapted primarily for vision at night. In some permanently aquatic species, they are reduced in size and have a simplified

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.[19]
To find their prey, salamanders use
trichromatic color vision extending into the ultraviolet range, based on three photoreceptor types that are maximally sensitive around 450, 500, and 570 nm.[20] 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.[8]

All salamanders lack middle ear cavity,

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.[23] 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 the animal of an approaching predator.[24]

Salamanders are usually considered to have no voice and do not use sound for communication in the way that frogs do; however, in mating system they communicate by pheromone signaling; some species can make quiet ticking. clicking, squeaks or popping noises,

Ichthyosaura alpestris in their aquatic phase.[27] Vocalization in salamanders has been little studied and the purpose of these sounds is presumed to be the startling of predators.[28]

Salamanders need moist environments to respire through their skin.

Respiration

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 the egg's surface.[29]

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 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.[29][30][31]

In the amphiumas, metamorphosis is incomplete, and they retain one pair of gill slits as adults, with fully functioning internal lungs.[32] 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 the olm, have both lungs and gills as adults.[8]

A dissected view of the levatores arcuum muscles in a Necturus maculosus specimen. These (shown in the purple circles) move the external gills, as a means of respiration.

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.

thyroid gland prevent the internalization of the external gills as seen in most salamanders that undergo metamorphosis.[34] The external gills seen in salamanders differs greatly from that of amphibians with internalized gills. Unlike amphibians with internalized gills which typically rely on 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.[35][36]

Feeding and diet

Salamanders are opportunistic

beetles, beetle larvae, leafhoppers, springtails, moths, spiders, grasshoppers, and mites.[37] Cannibalism sometimes takes place, especially when resources are short or time is limited. Tiger salamander tadpoles in ephemeral pools sometimes resort to eating each other, and are seemingly able to target unrelated individuals.[39] Adult blackbelly salamanders (Desmognathus quadramaculatus) prey on adults and young of other species of salamanders, while their larvae sometimes cannibalise smaller larvae.[40]

The head of a tiger salamander

Most species of salamander have small teeth in both their upper and lower jaws. Unlike

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 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.[41] 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.[42]

A terrestrial salamander catches its prey by flicking out its sticky tongue in an action that takes less than half 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.[43] 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 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 the throat, assisted by depression of the eyeballs into the roof of the mouth.[44] 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.[45][46] Muscles that originate in the pelvic region and insert in the tongue are used to reel the tongue and the hyoid back to their original positions.[47]

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 the prey, which is then swallowed.[47]

Though frequently feeding on slow-moving animals like

sirenids are unique among salamanders for having developed speciations towards herbivory, 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.[48]

Defense

Further information:
Antipredator adaptations

Salamanders have thin skins and soft bodies, and move rather slowly, and at first sight might appear to be vulnerable to opportunistic predation. However, they have several effective lines of defense. Mucus coating on damp skin makes them difficult to grasp, and 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 the future.[49]

Aposematism

Further information: aposematism
A fire salamander's striking black and yellow pattern warns off predators

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.[50] 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 the spray for a distance of up to 80 cm (30 in).[51]

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 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.[52]

Camouflage and mimicry

Further information: camouflage and mimicry

Although many salamanders have

nocturnal and are eaten by snakes, while the California newt has many large poison glands in its skin, is diurnal, and is avoided by snakes.[55]

Autotomy

Further information: autotomy

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 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.[56]

Distribution and habitat

Salamanders split off from the other amphibians during the mid- to late Permian, and initially were similar to modern members of the

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 the frogs and toads, within Batrachia. The earliest known salamander fossils have been found in geological deposits in China and Kazakhstan, dated to the middle Jurassic period around 164 million years ago.[57]

Salamanders are found only in the

Palaeoplethodon hispaniolae,[61] found trapped in amber in the Dominican Republic. However, possible salamander fossils have been found in Australia at the Murgon fossil site, representing the only known salamanders known from the continent.[62]

There are about 760 living species of salamander.[63][64] 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 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 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.[37]

One species, the Anderson's salamander, is one of the few species of living amphibians to occur in brackish or salt water.[65]

Reproduction and development

See also: Sexual selection in amphibians
Sierra newt amplexus found in stream at Woolman Semester in Nevada County, California

Many salamanders do not use vocalisations,

Plethodont species.[67]

Except for terrestrial species in the three families

spermatozoa move to the spermatheca, one or more chambers in the roof of the cloaca, where they are stored for sometimes lengthy periods until 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.[67][74]

Three different types of egg deposition occur.

ovoviviparous, with the female retaining the eggs inside her body until they hatch, either into larvae to be deposited in a water body, or into fully formed juveniles.[8]

Embryonic development of a salamander, filmed in the 1920s

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, 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,[75] narrower fins and no balancers, but instead have hind limbs already developed when they hatch.[76] The tadpoles are carnivorous and 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.[77]

By the end of the larval stage, the tadpoles already have limbs and metamorphosis takes place normally. In salamanders, this occurs over 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.[78]

Neotenic axolotl, showing external gills

Not all species of salamanders follow this path.

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.[78] This may be due to cold or wildly fluctuating temperatures, aridity, lack of food, lack of cover, or insufficient iodine for 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 the species to survive even when the terrestrial environment is too harsh for the adults to thrive on land.[76]

Conservation

The threatened hellbender

A general decline in living amphibian species has been linked with the fungal disease

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 it is important to note that 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.[80]

Various conservation initiatives are being attempted around the world. The

Qinling Mountains and captive breeding programmes have been set up.[82] The hellbender is another large, long-lived species with dwindling numbers and fewer juveniles reaching maturity than previously.[83] Another alarming finding is the increase in abnormalities in up to 90% of the hellbender population in the Spring River watershed in Arkansas.[84] 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.[85] Of 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 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.[86]

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 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 the local population on the restoration of the natural habitat of these creatures.[87] 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.[88] However, the axolotl has the benefit of being raised in farms for the purpose of research facilities. So there is still a chance that they may be able to return to their natural habitat. The recent decline in population has substantially impacted genetic diversity among populations of axolotl, making it difficult to further progress scientifically. It is important to note that although there is a level of limited genetic diversity due to Ambystoma populations, such as the axolotl, being paedeomorphic species, it does not account for the overall lack of diversity. There is evidence that points towards a historical bottlenecking of Ambystoma that contributes to the variation issues. Unfortunately, there is no large genetic pool for the species to pull from unlike in historical times. Thus there is severe concern for inbreeding due to lack of gene flow.[89] One way researchers are looking into maintaining genetic diversity within the population is via cryopreservation of 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 the salamander family.[88][90][91]

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 the cloacae of females. The results of this research may be used in captive-breeding programmes for endangered species.[92]

Taxonomy

The order name Urodela comes from the name Urodèles given by André Marie Constant Duméril in 1805,[2] it is derived from the Greek words οὐρά ourā́ "tail" and δῆλος dēlos "visible, conspicuous" because of their "persistent" tails.[93]

Disagreement exists among different authorities as to 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.[2][citation needed] Others restrict the name Caudata to the crown group and use Urodela for the total group.[94][95] The former approach seems to be most widely adopted and is used in this article.[64]

The ten families belonging to Urodela are divided into three suborders.[94] The clade Neocaudata is often used to separate the Cryptobranchoidea and Salamandroidea from the Sirenoidea.

Cryptobranchoidea (Giant salamanders)
Family Common names Example species

Example image

Cryptobranchidae
 Giant salamanders Hellbender (Cryptobranchus alleganiensis)
Hynobiidae
 Asiatic salamanders Hida salamander (Hynobius kimurae)
Salamandroidea (Advanced salamanders)
Ambystomatidae Mole salamanders Marbled salamander (Ambystoma opacum)
Amphiumidae
 Amphiumas or Congo eels Two-toed amphiuma (Amphiuma means)
Plethodontidae
 Lungless salamanders Red-backed salamander (Plethodon cinereus)
Proteidae Mudpuppies and olms Olm (Proteus anguinus)
Rhyacotritonidae
 Torrent salamanders Southern torrent salamander (Rhyacotriton variegatus)
Salamandridae Newts and true salamanders Alpine newt (Ichthyosaura alpestris)
Sirenoidea
 (Sirens)
Sirenidae Sirens Greater siren (Siren lacertina)

Phylogeny and evolution

The origins and evolutionary relationships between the three main groups of amphibians (gymnophionans, urodeles and anurans) is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggested that the first divergence between these three groups took place soon after they had branched from the lobe-finned fish in the Devonian (around 360 million years ago), and before the breakup of the supercontinent Pangaea. The briefness of this period, and the speed at which radiation took place, may help to account for the relative scarcity of amphibian fossils that appear to be closely related to lissamphibians.[96] However, more recent studies have generally found more recent (Late Carboniferous[97] to Permian[98]) age for the basalmost divergence among lissamphibians.

Karaurus sharovi

The earliest known salamander-line lissamphibian is Triassurus from the Middle-Late Triassic of Kyrgyzstan.[99] Other fossil salamanders are known from the Middle-Late Jurassic of Eurasia, including Kokartus honorarius from the Middle Jurassic of Kyrgyzstan, two species of the apparently neotenic, aquatic Marmorerpeton from the Middle Jurassic of England and Scotland,[100] and Karaurus from the Middle-Late Jurassic of Kazakhstan, resembled modern mole salamanders in morphology and probably had a similar burrowing lifestyle.[64] They looked like robust modern salamanders but lacked a number of anatomical features that characterise all modern salamanders.[101]

The two groups of extant salamanders are the

Upper Cretaceous, most or all of the living salamander families had probably appeared.[64]

The following cladogram shows the relationships between salamander families based on the molecular analysis of Pyron and Wiens (2011).[102] The position of the Sirenidae is disputed, but the position as sister to the Salamandroidea best fits with the molecular and fossil evidence.[64]

Cryptobranchoidea

Cryptobranchidae (giant salamanders & hellbenders)

Hynobiidae (Asiatic salamanders)

Sirenoidea

Sirenidae (sirens)

Salamandroidea
Treptobranchia

Salamandridae (true salamanders & newts)

Ambystomatidae (axolotls & tiger salamanders)

Dicamptodontidae
(Pacific giant salamanders)

Proteidae (olms & waterdogs)

Plethosalamandroidei

Rhyacotritonidae
(torrent salamanders)

Xenosalamandroidei

Amphiumidae (amphiumas)

Plethodontidae (lungless salamanders)

Genome and genetics

Salamanders possess gigantic genomes, spanning the range from 14 Gb to 120 Gb[103] (the human genome is 3.2 Gb long). The genomes of Pleurodeles waltl (20 Gb) and Ambystoma mexicanum (32 Gb) have been sequenced.[104][105]

Their giant genomes have strongly affected their physiology. This includes their skeletal and circulatory systems, and have led to a simplified brain, weak heart and slow metabolism.[106] The cell mechanisms that prevents transposons to accumulate seems to be partially defect in salamanders. Some species with the largest genomes have lost the ability to go through metamorphosis. The development of the body is slower than its growth compared to their ancestors, and stops at a certain age, leaving them with embryonic traits. The salamander tissues contain cells that differentiates slowly, weakly, or not at all, due to intron delay, which gives them regenerative properties, which includes regenerating parts of the face and eye, lungs, liver, heart, and even the spinal cord and brain, and they have been described as “walking bags of stem cells.”[107][108][109] Research has also shown that they do not develop typical signs of aging and do not accumulate age-related diseases like cancer.[110]

In human society

Myth and legend

Main article: Cultural depictions of salamanders
A salamander unharmed in the fire, 1350

Legends have developed around the salamander over the centuries, many related to fire. This connection likely originates from the tendency of many salamanders to dwell inside rotting logs. When the log was placed into a fire, the salamander would attempt to escape, lending credence to the belief that salamanders were created from flames.[111]

The association of the salamander with fire appeared first in Antiquity with

Saint Augustine in the fifth century and Isidore of Seville in the seventh century.[113][114]

Ukiyo-e print by Utagawa Kuniyoshi (1797–1861) depicting a giant salamander being stabbed by the samurai Hanagami Danjō no jō Arakage

The mythical ruler Prester John supposedly had a robe made from alleged salamander hair, in fact asbestos fibre, already known by ancient Greece and Rome (the linum vivum of Pliny the Elder Naturalis historia, 19, 4).[115] The "Emperor of India" possessed a suit made from a thousand skins; Pope Alexander III had a tunic which he valued highly and William Caxton (1481) wrote: "This Salemandre berithe wulle, of which is made cloth and gyrdles that may not brenne in the fyre."[116] The salamander was said to be so toxic that by twining around a tree, it could poison the fruit and so kill any who ate them and by falling into a well, could kill all who drank from it.[116]

In his autobiography, Benvenuto Cellini relates:

When I was about five, my father was sitting alone in one of our small rooms, singing and playing his viol. Some washing had just been done there and a good log fire was still burning. It was very cold, and he had drawn near the fire. Then, as he was looking at the flames, his eye fell on a little animal, like a lizard, that was running around merrily in the very hottest part of the fire. Suddenly realizing what it was, he called my sister and myself and showed it to us. And then he gave me such a violent box on the ears that I screamed and burst into tears. At this he calmed me as kindly as he could and said: 'My dear little boy, I didn't hit you because you had done wrong. I only did it so that you will never forget that the lizard you saw in the fire is a salamander, and as far as we know for certain no one has ever seen one before.'[117]

The Japanese giant salamander has been the subject of legend and artwork in Japan (e.g. the ukiyo-e work by Utagawa Kuniyoshi). The well-known Japanese mythological creature known as the kappa may be inspired by this salamander.[118]

Medical reseach

Salamanders'

macrophages were removed, salamanders lost their ability to regenerate and instead formed scar tissue. If the processes involved in forming new tissue can be reverse engineered into humans, it may be possible to heal injuries of the spinal cord or brain, repair damaged organs and reduce scarring and fibrosis after surgery.[121]

The spotted salamander (Amblystoma maculatum) lives in a symbiotic relationship with a green algae known as Oophila amblystomatis. The algal cells make their way into tissue cells throughout the embryo's body and appears to avoid rejection by activating genes which suppress the embryo's immune response. A mechanism that could be used in treatment for autoimmune diseases in humans.[122]

Brandy

A 1995 article in the Slovenian weekly magazine

hallucinogenic with aphrodisiac effects and is made by putting several live salamanders in a barrel of fermenting fruit. Stimulated by the alcohol, they secrete toxic mucus in defense and eventually die. Besides causing hallucinations, the neurotoxins present in the brew were said to cause extreme sexual arousal.[123]

Later research by Slovenian anthropologist Miha Kozorog (University of Ljubljana) paints a very different picture—Salamander in brandy appears to have been traditionally seen as an adulterant, one which caused ill health. It was also used as a term of slander.[124]

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Cited texts

External links

Wikispecies has information related to Urodela.
Wikimedia Commons has media related to Caudata.
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