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Salamander

Salamander
Temporal range: Middle Jurassic-Recent, 164–0Ma
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Spotted salamander, Ambystoma maculatum
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Superorder: Batrachia
Order: Caudata
Scopoli, 1777
Suborders

Cryptobranchoidea
Salamandroidea
Sirenoidea

Native distribution of salamanders (in green)

Salamanders are any of the approximately 655 extant and all the extinct species of amphibians within the order Caudata. The present-day species are often grouped together under the term Urodela. They are typically characterized by a superficially 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 larva and adult. Salamanders are almost entirely restricted to the northern hemisphere and are found in the Holarctic ecozone with a few species present in the Neotropical zone.

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 life, some take to the water intermittently, and others are entirely terrestrial as adults. Unique among vertebrates, they are capable of regenerating lost limbs, as well as other damaged parts of the body. Members of the Salamandridae family 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 and 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 there is great variation in the life cycle. In some species and in some harsh environments, salamanders reproduce while still in the larval state.

In literature and legend, the salamander is associated with fire, being supposedly unharmed by the flames, while clothes made from its skins or 'wool' were believed to be incombustible. More plausibly, salamanders were said to be intensely poisonous. Despite this, salamander brandy, a drink prepared by dunking live salamanders in fermenting fruit juices, is reputed to have hallucinogenic and aphrodisiac properties. The salamander's ability to regenerate lost body parts is being investigated and research is ongoing into any applications this may have for human medicine.

Contents

  • Morphology 1
    • Trunk, limbs and tail 1.1
    • Skin 1.2
    • Senses 1.3
    • Respiration 1.4
  • Feeding and diet 2
  • Defense 3
    • Aposematism 3.1
    • Crypsis and mimicry 3.2
    • Autotomy 3.3
  • Distribution and habitat 4
  • Reproduction and development 5
  • Conservation 6
  • Taxonomy 7
  • Phylogeny and evolution 8
  • In human society 9
    • Myth and legend 9.1
    • Limb regeneration as applied to humans 9.2
    • Salamander brandy 9.3
  • References 10
    • Cited texts 10.1
  • External links 11
    • Regional lists 11.1
    • Media 11.2

Morphology

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 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.[1]

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 (143 lb). Most, however, are between 10 and 20 cm (3.9 and 7.9 in) in length.[2]

Trunk, limbs and tail

Adult salamanders generally resemble small lizards, 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 the body.[3]

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 elongate, 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 sp. from California has feet with fleshy webs and short digits and uses its tail 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.[4]

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 autotomised when grabbed. Unlike frogs, an adult salamander is able to regenerate limbs and its tail when these are lost.[4]

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 cornified outer layers, renewed periodically through a skin shedding process controlled by the 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 arms 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.[5] The animal often then eats the resulting sloughed skin.[1]

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.[5] Some salamander toxins are particularly potent. The rough-skinned newt (Taricha granulosa) produces the neurotoxin tetrodotoxin (TTX), the most toxic non-protein 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.[6]

Mature adults of some salamander species have "nuptial" glandular tissue in the cloaca, at the base of the tail, on the head or under the chin. 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.[7] In some plethodonts, males have conspicuous mental glands on 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.[8] The gland at the base of the tail in Plethodon cinereus is used to mark fecal pellets to proclaim territorial ownership.[7]

Senses

The front part of the olm's head carries sensitive chemo-, mechano-, and electroreceptors.

nasolabial grooves, which stretch from the nostrils to the corners of the mouth. These extended areas seems to be associated with the identification of prey items, the recognition of conspecifics and the identification of individuals.[9]

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

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

Media

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

Regional lists

  • Tree of Life: Caudata
  • Salamander Gallery
  • Salamanders.nl – The Official Dutch Newt & Salamander Society Site
  • Caudata Culture
  • Salamandridae
  • Critter Crossings: Salamander Tunnels at Department of Transportation
  • Salamander at the Encyclopedia of Life
  • "Caudata".  
  • ArchéoZooThèque : Urodele skeleton drawing : available in vector, image and PDF formats

External links

  • Cott, Hugh B. (1940). Adaptive Coloration in Animals. Oxford University Press. 
  • Dorit, R. L.; Walker, W. F.; Barnes, R. D. (1991). Zoology. Saunders College Publishing.  
  • Kardong, Kenneth V. (2009). Vertebrates: Comparative Anatomy, Function, Evolution (5th ed.). McGraw-Hill.  
  • Cogger, H.G.; Zweifel, R.G., ed. (1998). Encyclopedia of Reptiles and Amphibians (2nd ed.). Academic Press.  
  • Stebbins, Robert C.; Cohen, Nathan W. (1995). A Natural History of Amphibians. Princeton University Press.  
  • *Regardie, Israel (2002). The Golden Dawn: the Original Account of the Teachings, Rites & Ceremonies of the Hermetic Order. Llewellyn Publications.  

Cited texts

  1. ^ a b c d e f Cogger & Zweifel (1998), pp. 60–68.
  2. ^ Stebbins & Cohen (1995) p. 3
  3. ^ Lopez, Carl H.; Brodie, Edmund D. Jr. (1972). "The Function of Costal Grooves in Salamanders (Amphibia, Urodela)". Journal of Herpetology 11 (3): 372–374.  
  4. ^ a b c Stebbins & Cohen (1995) pp. 26–30
  5. ^ a b Stebbins & Cohen (1995) pp. 10–16
  6. ^ Brodie, Edmund D. Jr. (1968). "Investigations on the skin toxin of the adult rough-skinned newt, Taricha granulosa". Copeia 1968 (2): 307–313.  
  7. ^ a b Wells, Kentwood, D. (2010). The Ecology and Behavior of Amphibians. University of Chicago Press. pp. 411–417.  
  8. ^ León, Ezequiel González; Ramírez-Pinilla, Martha Patricia (2009). (Caudata: Plethodontidae)"Bolitoglossa nicefori"The mental gland of . Amphibia-Reptilia 30: 561–569.  
  9. ^ Stebbins & Cohen (1995) pp. 37–40
  10. ^ Stebbins & Cohen (1995) pp. 42–44
  11. ^ Przyrembel, C.; Keller, B.; Neumeyer, C. (1995). "Trichromatic color vision in the salamander (Salamandra salamandra)". Journal of Comparative Physiology 176 (4): 575–586.  
  12. ^ Becker, R. P.; Lombard, R. E. (1977). "Structural correlates of function in the "opercularis" muscle of amphibians". Cell and Tissue Research 175 (4): 499–522.  
  13. ^ Stebbins & Cohen (1995) pp. 69–72
  14. ^ Stebbins & Cohen (1995) pp. 76–77
  15. ^ a b Stebbins & Cohen (1995) pp. 17–25
  16. ^ Cogger & Zweifel (1998), pp. 74–75.
  17. ^ Lanza, B.; Vanni, S.; Nistri, A. (1998). Cogger, H. G.; Zweifel, R. G., ed. Encyclopedia of Reptiles and Amphibians. Academic Press. p. 72.  
  18. ^ a b c Hairston, Nelson G. (1949). "The local distribution and ecology of the plethodontid salamanders of the southern Appalachians". Ecological Monographs 19 (1): 47–73.  
  19. ^ "Plethodontidae". AmphibiaWeb. Retrieved 2014-02-09. 
  20. ^ Koppes, Steve. "He ain't tasty, he's my brother". Ask a Biologist. Arizona State University. Retrieved 2014-02-08. 
  21. ^ "Desmognathus quadramaculatus". AmphibiaWeb. Retrieved 2014-02-09. 
  22. ^ Kardong (2009), pp. 505–506.
  23. ^ Stebbins & Cohen (1995) pp. 57–58
  24. ^ Stebbins & Cohen (1995) pp. 58–60
  25. ^ Larsen, John H. jr.; Guthrie, Dan J. (1975). "The feeding system of terrestrial tiger salamanders (Ambystoma tigrinum melanostictum baird)". Journal of Morphology 147 (2): 137–153.  
  26. ^ Deban, S.M., D.B. Wake, and G. Roth 1997. Salamander with a ballistic tongue. Nature 389: 27-28.
  27. ^ Deban, S. M., J.C. O’Reilly, U. Dicke, U. and J.L. van Leeuwen 2007. Extremely high-power tongue projection in plethodontid salamanders. Journal of Experimental Biology 210: 655-667.
  28. ^ a b Regal, Philip J. (1966). "Feeding specializations and the classification of terrestrial salamanders". Evolution 20 (3): 392–407.  
  29. ^ Stebbins & Cohen (1995) pp. 110–120
  30. ^ Mason, J. Russell; Rabin, Michael D.; Stevens, David A. (1982). "Conditioned taste aversions: skin secretions used for defense by tiger salamanders, Ambystoma tigrinum". Copeia 3: 667–671.  
  31. ^ Brodie, Edmund D. Jr.;  
  32. ^ Heiss, E.; Natchev, N.; Salaberger, D.; Gumpenberger, M.; Rabanser, A.; Weisgram, J. (2010). "Hurt yourself to hurt your enemy: new insights on the function of the bizarre antipredator mechanism in the salamandrid Pleurodeles waltl". Journal of Zoology 280 (2): 156–162.  
  33. ^ a b Howard, Ronnie R.; Brodie, Edmund D. Jr. (1973). "A Batesian mimetic complex in salamanders: responses of avian predators". Herpetologica 29 (1): 33–41.  
  34. ^ Kuchta, S. R.; Krakauer, A. H.; Sinervo, B (2008). "Why does the yellow-eyed ensatina have yellow eyes? Batesian mimicry of Pacific newts (genus Trachia) by the salamander Ensatina eschscholtzii xanthoptica". Evolution 62 (4): 984–990.  
  35. ^ Cott, 1940. Page 204.
  36. ^ Monaghan, James R.; Epp, Leonard G.; Putta, Srikrishna; Page, Robert B.; Walker, John A.; Beachy, Chris K.; Zhu, Wei; Pao, Gerald M.; Verma, Inder M.; Hunter, Tony; Bryant, Susan V.; Gardiner, David M.; Harkins, Tim T.; Voss, S. Randal (2009). "Microarray and cDNA sequence analysis of transcription during nerve-dependent limb regeneration". BMC Biology 7 (1).  
  37. ^ Gao, Ke-Qin; Shubin, Neil H. (2012). "Late Jurassic salamandroid from western Liaoning, China". Proceedings of the National Academy of Sciences of the United States of America 109 (15): 5767–5772.  
  38. ^ Wells, Kentwood D. (2007). The Ecology and Behavior of Amphibians. University of Chicago Press. p. 130.  
  39. ^ a b c Stebbins & Cohen (1995) pp. 143–154
  40. ^ a b Stebbins & Cohen (1995) pp. 175–179
  41. ^ "Plethodontidae". AmphibiaWeb. Retrieved 2014-01-09. 
  42. ^ a b Kiyonaga, Robin R. "Metamorphosis vs. neoteny (paedomorphosis) in salamanders (Caudata)". 
  43. ^ a b Sandoval-Comte, Adriana; Pineda, Eduardo; Aguilar-López, José L. (2012). "In search of critically endangered species: the current situation of two tiny salamander species in the neotropical mountains of Mexico". PloS ONE 7 (4): e34023.  
  44. ^ Fountain, Henry (2009-02-16). "Another Amphibian at Risk: Salamanders". The New York Times. Retrieved 2013-06-28. 
  45. ^ "Chinese Giant Salamander". ZSL Conservation. Zoological Society of London. Retrieved 2013-07-21. 
  46. ^ Wheeler, Benjamin A.; Prosen, Ethan; Mathis, Alicia; Wilkinson, Robert F. (2003). "Cryptobranchus alleganiensis"Population declines of a long-lived salamander: a 20+-year study of hellbenders, . Biological Conservation 109 (1): 151–156.  
  47. ^ Wheeler, Benjamin A.; McCallum, Malcolm L.; Trauth, Stanley E. (2002). ) in Arkansas: a comparison between two rivers with a historical perspective"Ctyptobranchm alleganiensis bishopi"Abnormalities in the Ozark hellbender (. Journal of the Arkansas Academy of Science 58: 250–252. 
  48. ^ "World's first captive breeding of Ozark hellbenders". Science Daily. 2011-12-01. Retrieved 2013-07-21. 
  49. ^ "Lungless salamanders of Mexico". EDGE: Evolutionary distinct and globally endangered. The Zoological Society of London. Retrieved 2013-07-21. 
  50. ^ Marcec, Ruth; Bement, Hannah. "Salamander Conservation". Amphibian Conservation. Memphis Zoo. Retrieved 2013-07-21. 
  51. ^ a b c d Naish, Darren (2013-10-01). "The amazing world of salamanders". Scientific American. Retrieved 2014-01-14. 
  52. ^ a b Larson, A.; Dimmick, W. (1993). "Phylogenetic relationships of the salamander families: an analysis of the congruence among morphological and molecular characters". Herpetological Monographs 7 (7): 77–93.  
  53. ^ San Mauro, Diego; Vences, Miguel; Alcobendas, Marina; Zardoya, Rafael; Meyer, Axel (2005). "Initial diversification of living amphibians predated the breakup of Pangaea". The American Naturalist 165 (5): 590–599.  
  54. ^ San Mauro, D. (2010). "A multilocus timescale for the origin of extant amphibians". Molecular Phylogenetics and Evolution 56 (3): 554–561.  
  55. ^ Marjanović, D., Laurin, M. (2007). "Fossils, molecules, divergence times, and the origin of lissamphibians". Systematic Biology 56 (3): 369–388.  
  56. ^ de Buffrénil, V., Canoville, A., Evans, S. E., Laurin, M. (2014). "Histological study of karaurids, the oldest known (stem) urodeles". Historical Biology.  
  57. ^ Marjanovic, D., Laurin, M. (2014). "An updated paleontological timetree of lissamphibians, with comments on the anatomy of Jurassic crown-group salamanders (Urodela)". Historical Biology.  
  58. ^ Blackburn, D.C.; Wake, D.B. (2011). "Class Amphibia Gray, 1825. In: Zhang, Z.-Q. (Ed.) Animal biodiversity: An outline of higher-level classification and survey of taxonomic richness". Zootaxa 3148: 39–55. 
  59. ^ Naish, Darren (1 October 2013). "Tetrapod Zoology: The Amazing World of Salamanders". Scientific American. Retrieved 15 January 2014. 
  60. ^ Ashcroft, Frances (2002). Life at the Extremes: The Science of Survival. University of California Press. p. 112.  
  61. ^ a b  
  62. ^  
  63. ^ Saint Augustine (5th Century AD). City of God. pp. Book 21, 4. 
  64. ^ Isidore of Seville (7th Century AD). Etymologies. pp. Book 12, 4:36. 
  65. ^ Regardie (2002).
  66. ^ Director: Duncan Chard (2012-02-14). "River Monsters". Programme 6, Series 3. ITV. ITV1.
  67. ^  
  68. ^ Keim, Brandon (2009-07-01). "Salamander discovery could lead to human limb regeneration".  
  69. ^ "Do salamanders' immune systems hold the key to regeneration?". ScienceDaily. Retrieved 2013-05-21. 
  70. ^ Goldsmith, Richard (2010-06-11). "Mind-Bending Hallucinogenic Drinks". Fox News. Retrieved 2014-01-02. 
  71. ^ Kozorog, Miha (2003). "Salamander Brandy: "A Psychedelic Drink" Between Media Myth and Practice of Home Alcohol Distillation in Slovenia". Anthropology of East Europe Review 21 (1): 63–71. Retrieved 2014-03-22. 

References

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.[71]

A 1995 article in the Slovenian weekly magazine Mladina publicized Salamander brandy, a liquor supposedly indigenous to Slovenia. It was said to combine 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.[70]

Salamander brandy

Salamanders' limb regeneration has long been the focus of interest among scientists. Researchers have been trying to find out the conditions required for the growth of new limbs and hope that such fibrosis after surgery.[69]

Limb regeneration as applied to humans

The Japanese giant salamander has been the subject of legend and artwork in Japan, in the ukiyo-e work by Utagawa Kuniyoshi. The well-known Japanese mythological creature known as the kappa may be inspired by this salamander.[66] A newt plays a key role in Roald Dahl's children's book Matilda when, in the chapter 'The First Miracle', the eponymous heroine Matilda Wormwood slips a newt into the headmistress Miss Trunchbull's water, and tips it over by telekinesis.[67]

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


  1. Spirits of Earth - Gnomes
  2. Spirits of Air - Sylphs
  3. Spirits of Water - Undines
  4. Spirits of Fire - Salamanders

In Hermetic teachings, there are four orders of elements and each has a ruling elemental over it:[65]

The association of the salamander with fire appeared first in Ancient Greece, where Pliny the Elder writes in his Natural History that "A salamander is so cold that it puts out fire on contact. It vomits from its mouth a milky liquid; if this liquid touches any part of the human body it causes all the hair to fall off, and the skin to change color and break out in a rash."[62] The ability to put out fire is repeated by Saint Augustine in the fifth century and Isidore of Seville in the seventh century.[63][64]

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.[60] The mythical ruler Prester John, supposedly had a robe made from salamander hair, 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."[61] 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.[61]

A salamander unharmed in the fire, 1350

Myth and legend

In human society

Cladogram from Darren Naish. The position of the Sirenidae is disputed; the position shown is considered by Naish to explain the data best.[59]

Caudata

†various fossils inc. Pangerpeton, Karauridae

Urodela
Cryptobranchoidea

Hynobiidae


Cryptobranchidae


Salamandroidea


Sirenidae

Treptobranchia


Ambystomatidae


Dicamptodontidae



Salamandridae





Proteidae

Plethosalamandroidei

Rhyacotritonidae

Xenosalamandroidei

Amphiumidae


Plethodontidae







All known fossil salamanders and all extinct species fall under the order Caudata, while sometimes the extant species are grouped together as the Urodela.[52][58] There are about 655 extant species of salamander.[51]

The Cryptobranchoidea (primitive salamanders) and the Salamandroidea, also known as Diadectosalamandroidei, (advanced salamanders) are believed to be sister groups. Both seem to have appeared before the end of the Jurassic, the former being exemplified by Chunerpeton tianyiensis, Pangerpeton sinensis, Jeholotriton paradoxus, Regalerpeton weichangensis, Liaoxitriton daohugouensis and Iridotriton hechti, and the latter by Beiyanerpeton jianpingensis. By the Upper Cretaceous, most or all of the living salamander families had probably appeared.[51]

The first known fossil salamanders are Kokartus honorarius from the Middle Jurassic of Kyrgyzstan and two species of the apparently neotenic, aquatic Marmorerpeton from England[56] of a similar date.[57] They looked superficially like robust modern salamanders but lacked a number of anatomical features that developed later. Karaurus sharovi from the Upper Jurassic of Kazakhstan resembled modern mole salamanders in morphology and probably had a similar burrowing lifestyle.[51]

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.[53] However, more recent studies have generally found more recent (Late Carboniferous[54] to Permian[55]) age for the basalmost divergence among lissamphibians.

Phylogeny and evolution

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)
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 (Ichthyosaura alpestris)
Sirenoidea (Sirens)
Sirenidae Sirens Greater siren (Siren lacertina)

The ten families belonging to the order Caudata are divided into three suborders.[52] The clade Neocaudata is often used to separate Cryptobranchoidea and Salamandroidea from the Sirenoidea.

There is disagreement between different authorities as to the definition of the terms "Caudata" and "Urodele". Some maintain that Urodela should be restricted to the crown group, with 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.[51]

Taxonomy

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 cloacas of females. It is hoped to use the results of this research in captive breeding programmes for endangered species.[50]

Various conservation initiatives are being attempted around the world. The Chinese giant salamander, at 1.8 metres (6 feet) 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.[45] The hellbender is another large, long-lived species with dwindling numbers and fewer juveniles reaching maturity than previously.[46] Another alarming finding is the increase in abnormalities in up to 90% of the hellbender population in the Spring River (Arkansas) watershed.[47] 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.[48] Of the twenty 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.[49]

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 the last few decades of the 20th century, although no direct link between the fungus and the population decline has yet been found.[43] 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 the cloud forests of Guatemala and Mexico during the 1970s were found by 2009 to be rare. [44] However, little data has 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.[43]

The threatened hellbender

Conservation

Not all species of salamander 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 the control of thyroid hormones and it seems that in obligate neotenes such as the axolotl (Ambystoma mexicanum), the tissues are 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.[42] 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 form. Neoteny allows the species to survive even when the terrestrial environment is too harsh for the adults to thrive on land.[40]

Neotenic axolotl, showing external gills

By the end of the larval stage, the tadpoles already have limbs and metamorphosis normally takes place. 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.[42]

[41] 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.carnivorous The tadpoles are [40] In temperate regions, reproduction is usually seasonal and salamanders may migrate to breeding grounds. Males usually arrive first and in some instances set up

Embryonic development of a salamander, filmed in the 1920s

There are three different types of egg deposition. Ambystoma and Taricha spp. spawn large numbers of small eggs in quiet ponds where there are unlikely to be many large predators. Most dusky salamanders (Desmognathus) and Pacific giant salamanders (Dicamptodon) lay smaller batches of medium-sized eggs in 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.[39] Some species such as the fire salamanders (Salamandra) are 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.[1]

In about 90% of all species, fertilisation is internal. The male typically deposits a spermatophore on the ground or in 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 there is often an elaborate courtship behavior 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. Here they are stored for sometimes lengthy periods until the eggs are laid. In the most primitive salamanders such as the Asiatic salamanders and the giant salamanders, external fertilization occurs instead. In these species, the male releases sperm onto the egg mass in a reproductive process similar to that of typical frogs.[39]

Salamanders are non-vocal and in most species the sexes look alike, so they use olfactory and tactile cues to identify potential mates. 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., the males are sexually dimorphic and display in front of the females. Visual cues are also thought to be important in some Plethodont species.[39]

Sierra newt amplexus found in stream at Woolman Semester in Nevada County, California

Reproduction and development

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 metres (3,000 feet) 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.[18]

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 Asian species, Salamandrella keyserlingii 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 the Alaska Panhandle.[38]

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. 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.[37]

Distribution and habitat

Some salamander species use tail autotomy to escape predators. The tail drops off and wriggles around for a little 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.[36]

Autotomy

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 will posture if attacked, revealing 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 thirty minutes after being swallowed (later being regurgitated).[33] 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.[33] Other species exhibit similar mimicry. In California, 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.[34] There is a correlation 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 the California newt has many large poison glands in its skin, is diurnal, and is avoided by snakes.[35]

Crypsis and mimicry

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 of 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.[32]

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.[30] 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 centimetres (31 in).[31]

Fire salamander's striking black and yellow pattern emphasizes body shape to warn off predators.

Aposematism

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 the 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 future.[29]

Defense

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.[28]

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.[24] 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.[25] Many lungless salamanders of the Family Plethodontidae have a more elaborate feeding method. 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.[26][27] 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 position.[28]

Most species of salamander have small teeth in both the upper and lower jaws. Unlike frogs, even the larvae of salamanders possess these teeth.[1] 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 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.[22] 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.[23]

The head of a tiger salamander

[21]) prey on adults and young of other species of salamander, while their larvae sometimes cannibalise smaller larvae.Desmognathus quadramaculatus (blackbelly salamanders Adult [20] 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.Cannibalism [18].mites and grasshoppers, spiders, moths, springtails, leafhoppers, beetle larvae, beetles, flies, earthworms, the diet included Appalachian Mountains) in the Desmognathus (dusky salamanders In a study of smaller [19]) eat crabs, fish, small mammals, amphibians and aquatic insects.Andrias japonicus (Japanese giant salamander Large species such as the [18] Salamanders are opportunistic

Feeding and diet

In the Amphiumas, metamorphosis is incomplete, and they retain one pair of mammals. Many species, such as the olm, have both lungs and gills as adults.[1]

When present in adult salamanders, lungs vary greatly among different species in size and structure. In aquatic, cold-water species like the southern torrent salamander (Rhyacotriton variegatus), 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 terrestrial lungless salamanders (family Plethodontidae), there are no lungs or gills, and gas exchange mostly takes place through the skin, 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.[15][16]

Respiration differs among 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 the egg's surface.[15]

Respiration

Salamanders are usually considered to have no voice and do not use sound for communication in the way that frogs do, however, some species can make quiet ticking or popping noises, perhaps by the opening and closing of valves in the nose. 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 a hissing sound, while the sirens sometimes produce quiet clicks, and can resort to faint shrieks if attacked. Vocalization in salamanders has been little studied and the purpose of these sounds is presumed to be the startling of predators.[14]

Salamanders lack eardrums, but like frogs have an opercularis system in the middle ear. This consists of two ossicles: 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.[12] The system seems able to detect low frequency vibrations (500–600 Hz) which may be picked up from the ground by the forelimbs and transmitted to the inner ear. These may serve to warn the animal of an approaching predator.[13]

[1]

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