Salamander

For other uses, see Salamander (disambiguation) and Caudata (disambiguation).

Salamander Temporal range: Middle Jurassic-Recent, 164–0Ma PreЄ Є O S D C P T J K Pg N
Spotted Salamander, Ambystoma maculatum
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Amphibia
Subclass:	Lissamphibia
Order:	Caudata Scopoli, 1777
Suborders
Cryptobranchoidea Salamandroidea Sirenoidea
Native distribution of salamanders (in green)

Salamanders are any of approximately 550 extant species of amphibians within the order Caudata. They are typically characterized by a superficially lizard-like appearance, with slender bodies, short noses, and long tails. All known fossil salamanders and all extinct species fall under the order Caudata, while sometimes the extant species are grouped together as the Urodela. Salamanders have never more than four toes on their front legs and five on their rear legs, but some species have fewer. Their moist skin usually makes them reliant on habitats in or near water, or under some protection (e.g., moist ground), often in a wetland. Some salamander species are fully aquatic throughout life, some take to the water intermittently, and some are entirely terrestrial as adults. Unique among vertebrates, they are capable of regenerating lost limbs, as well as other body parts. Many of the members of the family Salamandridae are known as newts.

The earliest known salamander fossils have been found in geological deposits of China and Kazakhstan, which have been dated to the middle Jurassic period, up to 164 million (plus or minus 4 million) years ago.

Physical characteristics

Mature salamanders generally have a basal tetrapod body form with a cylindrical trunk, four limbs and a long tail. Some species such as sirens and amphiumas have reduced or absent hindlimbs, giving them a more eel-like appearance. Most species have four clawless toes on the forelimbs and five on the hind limbs. 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 that is 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.

Salamanders range in size from the minute salamanders, with a total length of 2.7 cm (1.1 in), including the tail, to the Chinese giant salamander which reaches 1.8 m (5.9 ft) and weighs up to 65 kg (140 lb). Most, however, are between 10 and 20 cm (3.9 and 7.9 in) in length.

A fire salamander in Mount Olympus National Park, Greece

Physiology

Respiration differs among the different species of salamanders. Species that lack lungs respire through gills. In most cases, these are external gills, visible as tufts on either side of the head, although the amphiumas have internal gills and gill slits. 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.

Some terrestrial species lack both lungs and gills and perform gas exchange through their skin, a process known as valerian respiration in which the capillary beds are spread throughout the epidermis, and inside the mouth. Even some species with lungs can respire through the skin in this manner.

The skin of salamanders secretes mucus, which helps keep the animal moist when on dry land, and maintains their salt balance while in water, as well as providing a lubricant during swimming. Salamanders also secrete poison from glands in their skin, and some additionally have skin glands for secreting courtship pheromones. Salamanders regularly shed the outer layer of their skin (the epidermis) as they grow, and then eat the resulting slough.

Feeding

The head of a salamander

Terrestrial salamanders catch their prey by rapidly extending a sticky tongue which adheres to the prey, allowing it to be pulled into the mouth. In combination with tongue movements, salamanders may lunge forward and grasp prey with their jaws, securing them with small teeth on the margins of their jaws.

In the lungless salamanders, muscles surrounding the hyoid bone contract to create pressure and actually "shoot" the hyoid bone out of the mouth along with the tongue. The tip of the tongue is composed of a mucus which creates a sticky end to which the prey is captured. Muscles in the pelvic region are used in order to reel the tongue and the hyoid back to its original position.

Many of the highly aquatic species, however, lack muscles in the tongue, and do not use it for capturing prey, while most other species have a mobile tongue, but without the adaptations to the hyoid bone. Most species of salamander have small teeth in both the upper and lower jaws. Unlike frogs, even the larvae of salamanders possess these teeth.

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 nm, 500 nm and 570 nm. Permanently subterranean salamanders have reduced eyes, which may even be covered by a layer of skin. 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. Salamanders have no external ear, and only a vestigial middle ear.

Defense

Some salamander species use tail autotomy to escape predators. The tail will drop off and wriggle around for a little while, and the salamanders will either run away or stay still enough to not be noticed while the predator is distracted. Salamanders routinely regenerate complex tissues, including the lens or retina of the eye. Within only a few weeks of losing a piece of limb, a salamander perfectly reforms the missing structure. They can also produce a white, milky, poisonous substance.

Distribution

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, and they are no more closely related to lizards than they are to mammals. Their nearest relatives are the frogs and toads, within Batrachia.

Caudates are found exclusively in 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 species, Salamandrella keyserlingii occurring in the Siberian larch forests of Sakha and of the most northerly species in North America, Ambystoma laterale reaching no further than Labrador and Taricha granulosa not beyond the Alaska Panhandle. One-third of the known salamander species are found in North America. The highest concentration of these is found in the Appalachian Mountains region.

Development

The life history of salamanders is similar to that of other amphibians, such as frogs and toads. Most species fertilize the eggs internally, with the male depositing a sac of sperm in the female's cloaca. The most primitive salamanders – those grouped together as the Cryptobranchoidea – instead exhibit external fertilization. The eggs are laid in a moist environment, often a pond, but sometimes moist soil, or inside bromeliads. Some species are ovoviviparous, with the female retaining the eggs inside her body until they hatch.

A larval stage follows in which the organism is fully aquatic or water-dwelling, and possesses gills. Depending on species, the larval stage may or may not possess legs. The larval stage may last from days to years, depending on the species. Some species (such as Dunn's salamander) exhibit no larval stage at all, with the young hatching as miniature versions of the adult. Neoteny has been observed in all salamander families, in which an individual may retain gills into sexual maturity. This may be universally possible in all salamander species. More commonly, however, metamorphosis continues with the loss of gills, the growth (or increase in size) of legs, and the capability of the animal to function out of the water.

Declining populations

A general decline in living amphibian species, caused by the fungal disease chytridiomycosis, has had a significant effect on the salamander, as well. While researchers have not yet found a direct link between the fungus and the population decline, they do believe it has played a role. Researchers also cite deforestation and climate change as possible contributing factors, based on surveys conducted in Guatemala during the 1970s, as well as recently. Especially affected were Pseudoeurycea brunnata and Pseudoeurycea goebeli, both of which were abundant during the 1970s.

Taxonomy

The 10 families belonging to the order Caudata are divided into three suborders. The clade Neocaudata is often used to separate Cryptobranchoidea and Salamandroidea from the Sirenoidea.

Cryptobranchoidea (Giant salamanders)
Family	Common names	Example species	Example Photo
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)
Dicamptodontidae	Pacific giant salamanders	Pacific giant salamander (Dicamptodon tenebrosus)
Plethodontidae	Lungless salamanders	Red back 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 (Triturus alpestris)
Sirenoidea (Sirens)
Sirenidae	Sirens	Greater siren (Siren lacertina)

Phylogeny

Caudata †Bissektia nana †Marmorerpeton †Kiyatriton leshchinskiyi †Hemitrypus jordanianus †Jeholotriton paradoxus †Laccotriton subsolanus †Pangerpeton sinensis †Prosiren elinorae {Prosirenidae} †Sinerpeton fengshanensis †Triassurus sixtelae {Triassuridae} †Vaughniella urodeloides †Karauridae Urodela †Liaoxitriton Cryptobranchoidei †Regalerpeton weichangensis †Nesovtriton mynbulakensis Hynobiidae Cryptobranchidae Diadectosalamandroidei †Apricosiren ensomi †Beiyanerpeton jianpingensis †Galverpeton ibericum †Comonecturoides marshi †Hylaeobatrachus croyii †Iridotriton hechti †Valdotriton gracilis †Scapherpetontidae †Batrachosauroididae Sirenidae Proteidae Treptobranchia Ambystomatidae Dicamptodontidae Salamandridae Plethosalamandroidei Rhyacotritonidae Xenosalamandroidei Amphiumidae Plethodontidae

Urodela Hynobiidae Cryptobranchidae Rhyacotritonidae Amphiumidae Plethodontidae Hydatinosalamandroidei Perrenibranchia Proteidae Sirenidae Ambystomatidae Salamandridae

Urodela Sirenidae Neocaudata Hynobiidae Cryptobranchidae Proteidae Rhyacotritonidae Amphiumidae Plethodontidae Salamandridae Ambystomatidae Dicamptodontidae

Cladograms based on the work of Wiens et al. (2005)., Marjanovic & Laurin (2007) (A), Frost et al. (2006) (B) and Zhang & Wake (2009) (C).

Mythology and popular culture

A salamander unharmed in the fire

Main articles: Salamander (legendary creature) and Legendary salamander in popular culture

Numerous 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 placed into a fire, the salamander would attempt to escape from the log, lending to the belief that salamanders were created from flames — a belief that gave the creature its name.

Associations of the salamander with fire appeared first in the writings of Aristotle and Pliny, even mentioned in the Talmud, later writers during and after the middle ages like Leonardo da Vinci, Paracelsus, Conrad Lycosthenes, Benvenuto Cellini and Jean-Jacques Rousseau mentioned this association, more recently writers like Victor Hugo, Ray Bradbury, David Weber and J. K. Rowling.

Implications of limb regeneration as applied to humans

Salamanders' limb regeneration has been the focus of significant interest among scientists. Researchers have been trying to find out the conditions required for regeneration. A theory persists in the scientific community that such regeneration could be artificially recreated in humans using stem cells. Axolotls have been highlighted for research. Research published in the National Academy of Sciences researchers from the Australian Regenerative Medicine Institute have found that when macrophages were removed, salamanders lost their ability to regenerate and formed scarred tissue instead. The salamander is considered as the epitome of perfect regeneration and besides that, it may also have applications in healing injuries related to the spinal cord or brain and improvement in treatments which are linked to fibrosis or scarring.

References

• San Mauro, Diego; Miguel Vences, Marina Alcobendas, Rafael Zardoya and Axel Meyer (May 2005). "Initial diversification of living amphibians predated the breakup of Pangaea". American Naturalist 165 (5): 590–599. doi:10.1086/429523. PMID 15795855. 
• San Mauro, Diego (2010). "A multilocus timescale for the origin of extant amphibians". Molecular Phylogenetics and Evolution 56 (2): 554–561. doi:10.1016/j.ympev.2010.04.019. PMID 20399871. 

External links

• Tree of Life: Caudata
• Salamander Gallery
• Salamanders.nl - The Official Dutch Newt & Salamander Society Site
• Caudata Culture
• Salamandridae
• Urodela Info Center at Google Groups
• Critter Crossings: Salamander Tunnels at Department of Transportation
• Salamander at the Encyclopedia of Life
• "Caudata". Integrated Taxonomic Information System. 
• ArchéoZooThèque : Urodele skeleton drawing : available in vector, image and PDF formats

Regional lists

• Salamanders of Arkansas
• California Salamanders
• Salamanders of North Carolina
• Salamanders of Texas

Media

• Salamander Video
• Salamander feeding movies in slow motion
• Living Underworld salamander images
• Caudata-database: Images of newts and salamanders