Caudate Families

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The tailed amphibians known as caudates make up around 9% of the world's amphibian species. Order Caudata contains 9 families that are mainly distributed across the northern temperate regions of the world where cool and moist environments occur. A small number of species inhabit sub-tropical and tropical regions. The largest density of species is found in North America, where 8 of the 9 families are represented.

Woodland stream habitat. Photo: John Clare

Members of the order Caudata are commonly known as salamanders but also include newts, a group of species belonging to the family Salamandridae. A large proportion has a biphasic life cycle, starting life as aquatic gilled larvae that later metamorphosing into terrestrial adults. Adults usually follow seasonal breeding activity, migrating to breeding sites to court and lay eggs. Caudates are generally nocturnal and forage for food at night. Terrestrial adults generally remain hidden under logs and rocks during the day, while aquatic caudates live on the bottoms of streams or ponds, taking refuge under stones and detritus.

Families and Genera

The order Caudata contains nearly 600 species belonging to 9 families. The exact numbers and names of species change as species are discovered or redefined. Recent taxonomic changes are listed in the Taxonomic Revisions page. If you are primarily interested in captive care information, see Caresheets.

Ambystomatidae - Mole Salamanders, Hallowell 1856

Ambystoma annulatum
Photo: John Clare

The family Ambystomatidae is endemic to North America and widespread across the continent. This family is comprised of 2 genera, Ambystoma and Dicamptodon. They are medium to large salamanders characterized by short, rounded heads, prominent costal grooves and robust bodies and limbs. Terrestrial adults generally spend most of the year underground in burrows, emerging to breed en masse during the spring. Courtship normally takes place in pools where eggs are laid in clumps; however, some species breed during the autumn, and at least one species lays eggs near water on dry land, which becomes flooded during spring rains. Ambystomid larvae are characterized by broad heads, caudal fins and long filamentous gills. Certain species are obligate neotenes, such as the Axolotl (Ambystoma mexicanum) that retain larval characteristics into adulthood. Others display facultative metamorphosis whereby individuals retain the possibility of remaining in larval form under certain environmental conditions. The majority however, do metamorphose.

In 2006 the family Dicamptodon was placed back within the family Ambystomatidae. The genus Dicamptodon contains the largest terrestrial salamanders, reaching up to 35 cm (13.8 in.) in length. All species are distributed along the Pacific coast of the western United States where they inhabit coniferous forests with streams and springs. Larvae can take up to 4.5 years to reach metamorphosis, although one species, D. copei, lacks metamorphosis.

Amphiumidae, Gray 1825

Genera & Common names
Amphiuma (3)

Amphiuma means
Photo: Pierson Hill

The Amphiumidae family is comprised of 3 species within 1 genus. The family contains the longest and most massive salamanders in the United States; adults range from 33 - 117 cm (13 - 46 in.) in total length depending on species. Amphiumas are elongate, cylindrical, eel-like salamanders with 4 significantly reduced limbs that are typically less than 1 cm (0.4 in.) in length. They have 1, 2 or 3 toes on each foot, depending on the species. The tail is laterally compressed and makes up approximately 20-25% of the total body length. The skin of adults produces slippery mucus; larger amphiumas can produce a powerful bite. Teeth are present on the premaxillary, maxillary, vomerine, and mandibular bones. Metamorphosed individuals retain some larval features (i.e., paedomorphic) such as lack of eyelids and tongue and a gill slit in the pharyngeal region. Lungs are present, but amphiumas can also breathe via the pharynx and skin. Fertilization is internal and occurs via spermatophore transfer; females are often found guarding their eggs. Hatchlings are born with external gills that disappear at metamorphosis. Amphiumas are aquatic, although they may be found on land at night during rainstorms or when females are brooding eggs. Amphiumas inhabit swamps, lakes, marshes, drainage ditches and sluggish streams in the southeastern United States. If their habitat dries, amphiumas hide in holes where they may aestivate.

Cryptobranchidae - Giant Salamanders, Fitzinger, 1826

Andrias davidianus
Photo: Paul Bachhausen

Three species within 2 genera make up the family Cryptobranchidae, which contains the largest living amphibians, up to 1.5 m (59 in.) in total length. The largest species are found in the genus Andrias which occurs in Japan and China. The single member of the genus Cryptobranchus lives in eastern North America, and is commonly known as the Hellbender. Cryptobranchids are bulky, sturdy salamanders with large folds of skin running down the lower flanks of the body; these skin folds increase the surface area of skin for oxygen absorption. They are fully aquatic, never leaving the streams and rivers they inhabit. Metamorphosis is incomplete, with adults retaining gill slits despite the disappearance of external gills. Eyes lack eyelids and are very small, giving these animals poor eyesight. Sensory nodes in the head are used to detect changes in water pressure and locate prey. Adaptations to the mouth allow suction feeding. During breeding, territorial males build dens or nests that are visited by females who lay strings of paired eggs; eggs are then externally fertilized. Males guard eggs until they hatch, which can be as long as 3 months.

Hynobiidae - Asian Salamanders, Cope 1859

Hynobius tokyoensis egg sacs
Photo: Tim Johnson

Hynobiidae are small to medium sized salamanders distributed in Asia, with one species encroaching into European Russia. All have a biphasic life cycle with aquatic larvae and terrestrial adults. This family is considered a sister group of the giant salamanders, Cryptobranchidae. The Hynobiids are considered to be the most primitive of all living salamanders; thus they are likely to be the living salamanders that most closely resemble the common ancestors of all salamanders. Lungs are present in all except the genus Onychodactylus, which is lungless. Hynobiids lay curved-shaped gelatinous egg sacs containing many eggs. These are attached to vegetation or stones underwater, where they are externally fertilized by the male. Hynobiids lay eggs in still-water ponds or streams, depending on the species. Male parental care of eggs has been observed in some species. Larvae have 4 pairs of gill slits and external gills. Large-headed cannibalistic larvae have been observed in some species.

Proteidae - Mudpuppies and Waterdogs, Gray 1825

Necturus maculosus
Photo: Mike Graziano

The small family, Proteidae, consists of 2 genera that are widely separated in distribution. Necturus spp. are endemic to North America and are found in the eastern United States into southern Canada, while the monotypic genus Proteus is endemic to Europe and is distributed in parts of Italy, Slovenia, Croatia, Bosnia and Herzegovina. All species in this family are medium to large in size and are neotenic, retaining larval characteristics as adults, i.e., external gills and a flattened tail. The coloration of Necturus spp. is generally dark, mottled, or heavily spotted, while Proteus anguinus has little pigmentation. Necturus spp. are found in lakes, ponds, rivers, streams, and other freshwater environments. Proteus is found strictly in underground freshwater streams. Due to the neotenic nature of this family, they remain fully aquatic throughout all stages of their life cycle. Larvae are similar in overall appearance to the adults, although coloration can differ substantially from larvae to adult in some species. Most species are considered abundant, except N. alabamensis and P. anguinus, which are protected.

Rhyacotritonidae - Torrent Salamanders, Tihen 1958

Genera & Common names
Rhyacotriton (4) - Torrent salamanders

Rhyacotriton kezeri
Photo: Josef Uyeda

Members of the family Rhyacotritonidae are found in northwestern coastal and the Cascade Range regions of the United States - northern California, Oregon and Washington. They are all small (8 - 10 cm, 3 - 4 in.) salamanders with broad heads, stocky bodies, large prominent eyes and costal grooves. Until 1987 Rhyacotrition was considered a single species and placed within the Ambystomatidae or Dicamptodon families. In 1992 Good & Wake formally recognized Rhyacotriton as a distinct family. The family contains a single genus. Adult torrent salamanders are generally semi-aquatic, inhabiting stream habitats where they hide amongst the rocks. Adults also utilize moist forest habitats. Eggs are internally fertilized and laid under rocks in well-aerated water. Larvae are aquatic. Non-functioning vestigial lungs are present in adults. Populations of these salamanders are associated with old-growth forest habitats and do not tolerate logging (Good and Wake, 1992).

Salamandridae - True Newts and Salamanders, Gray 1825

Ommatotriton ophryticus
Photo: Jean-Pierre Collet

Family Salamandridae is unofficially subdivided into two main subgroups, "true salamanders" and "newts". The family is large, having about 80 species within 21 genera and is distributed across much of the temperate northern hemisphere: it is well represented in Europe, North America, and Asia. True salamanders however, are almost exclusively European in distribution, with the exception of some marginal populations in northwest Africa, Turkey and the Middle East. The genera Taricha and Notophthalmus are both endemic to the United States.

Cynops pyrrhogaster
Photo: Mark Aartse-Tuyn

Newts of the family Salamandridae are distinct from all other salamanders in that they have rough-textured skin. Most species have a biphasic life history, with aquatic larvae and metamorphosed adults that may be terrestrial or aquatic. Most family members are egg-layers, although some Salamandra populations give birth to fully-formed larvae or metamorphs. Internal fertilization is achieved for all Salamandrids through transfer of a spermatophore, which the male persuades the female to take up through elaborate courtship maneuvers. During the aquatic breeding season adult males often develop dorsal tail and body fins. This breeding 'dress' is most notable in the genera Triturus and Ommatotriton. Larvae are characterized by 4 pairs of large external gills and well developed long legs.

All Salamandrids produce toxic skin secretions as a defense mechanism and often display bright warning coloration. Some of the most striking examples of warning coloration can be seen in Salamandra species that sport yellow or orange patterning against a black background. Species with enlarged parotoid glands usually highlight them with conspicuous colors. Tetrodotoxin, the neurotoxin in skin secretions is found in the highest concentration in members of the genus Taricha; levels present are potent enough to kill most predators.

Sirenidae - Sirens, Gray 1825

P. striatus spheniscus
Photo: Pierson Hill

The Sirenidae family is comprised of 2 genera, Siren and Pseudobranchus. All sirenid adults have elongated, slender, eel-shaped bodies and range in length from as little as 10 cm (4 in.) in dwarf sirens to 99 cm (39 in.) in greater sirens. All species are perennibranchs and aquatic; the pelvic girdle and hind limbs are absent in all species but small forelimbs with toes are present. The complete absence of hind limbs distinguishes sirenids from all other salamanders.Adults exhibit larval characteristics such as the absence of eyelids and the presence of gill slits and external gills. Instead of premaxillary teeth, they have a horny beak. Sirenids are mostly found in the southeastern and southern United States and northeastern Mexico inhabiting heavily vegetated, still to slow-moving shallow waters that are often swamp-like with muddy substrates. Sirenids are known to aestivate and burrow in mud when in habitats subject to drought. The mode of sperm transfer between males and females has not been documented, but it is assumed that fertilization is external. Males do not produce spermatophores and females lack a spermotheca (reproductive sac for sperm storage). Eggs are laid attached to vegetation, singly or in clusters.

Plethodontidae - Lungless Salamanders, Gray 1850

Pseudotriton ruber ruber
Photo: Jim Anno

The family Plethodontidae, commonly known as the lungless salamanders, is widely distributed in eastern and western North America, and Central America with populations occurring in South America. The family also has limited distribution in southern Europe and Korea. Plethodontidae is the largest of all the caudate families and contains more than 390 species; the majority of the world's known salamander species reside in this family. Plethodontids inhabit a large range of environmental niches, ranging from aquatic or semi-aquatic, to terrestrial and even arboreal. Some genera and sub-genera retain a biphasic life cycle with aquatic larvae and terrestrial adults. With the exception of a few aquatic species such as the Desmognathus, most Plethodontids lack aquatic larvae and hatch as miniature adults from eggs laid terrestrially or arborealy.

Plethodon ouachitae
Photo: John Clare

Members of the Bolitoglossids, which are found in Central and South America, have evolved extensively, particularly in the tropics where highly arboreal and fossorial groups are found. Webbed feet are observed in some Bolitoglossids as an adaptation to life on moist vegetation, and elongated body shapes are found among the tropical fossorial genera. Climbing abilities are also seen in some temperate Plethodontid species such as Aneides, Plethodon and Hydromantes, some of which have adaptations for climbing on rock surfaces.

Plethodontids are highly variable in shape and size. One species is less than 3 cm (1.2 in.) in length when fully grown, whereas others reach over 30 cm (12 in.) in length. All Plethodontidae are lungless and respire through their skin, which needs to be kept moist as a consequence. One feature that distinguishes the family is the presence of a vertical groove found on the upper lip, known as the naso-labial groove. Male salamanders often have protuberances called cirri associated with these grooves, and both of these adaptations are thought to enhance the animals' chemoreception during breeding.

In 2005 a new species of Plethodontid was surprisingly found in Korea, the first of its kind in Asia, and given its own genus, Karsenia. This discovery along with the presence of Speleomantes in Europe, suggests that family Plethodontidae was once distributed much more widely throughout the northern continents.

References

Duellman, William E. and Trueb, Linda. 1994. Biology of Amphibians. Johns Hopkins University Press.
Good, David A. and Wake, David B. 1992. Geographic variation and speciation in the Torrent Salamanders of the genus Rhyacotriton (Caudata: Rhyacotritonidae). Zoology 126: 1-91.
Larson, Allen, Wake, David, and Devitt, Tom. Tree of Life Web Project. http://tolweb.org/Caudata. Accessed January 2010.
AmphibiaWeb - http://www.amphibiaweb.org. Accessed January 2010.
Petranka, James W. 1998. Salamanders of the United States and Canada. Smithsonian Institute Press.
Thorn, Robert and Raffaëlli, Jean. Les Salamandres de l'Ancien Monde. 2001, Societé Nouvelle des Editions Boubée Paris.

Posted April 2010. Written and compiled by Mark Aartse-Tuyn, Ryan St. Laurent, Jennifer Macke & Janice Williams. Map images by Will Jones.

Caudate Families

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