Salamanders and newts comprise one of three
groups of amphibians living today. The other
two, the caecilians (Gymnophiona) and the frogs
and toads (Anura) can be readily distinguished by
their body forms. Like other amphibians, salamanders
and newts have glandular skin that lacks
scales, feathers, or hair. Considering only species
living today, salamanders and newts are a small
group compared to the number of species of frogs
and toads. Whereas frogs and toads are represented
by about four thousand species, only about
four hundred species of salamanders and newts
are living today.
Systematists, biologists who study the classification
of plants and animals, recognize ten families
of salamanders. Newts are simply salamanders
that are classified in the family Salamandridae;
they can be distinguished fromother salamanders
by many osteological (bony) features and by their
generally rough skin, compared to the smooth
skin of other salamanders.
Anatomy of Salamanders and Newts
Salamanders have long, lizardlike bodies with long tails and four small legs. Many species have costal grooves along the sides of the body; the number of these grooves varies among species and can help with identification. Olfaction (sense of smell) is used during courtship, and males of many species have specialized glands on the body. Males of many species of lungless salamanders have a gland on the chin that is used to deliver hormones to the female during courtship. Salamanders have a larval stage, but unlike frogs and toads, in which the tadpole is very different from the adult frog, larval salamanders are similar in body form to adults. Larval forms are frequently found in water and retain external gills, which are lost at metamorphosis (transformation to the adult stage). Species that breed in ponds, where oxygen levels are low, have large, bushy gills for added surface area to increase the intake of oxygen. In contrast, species that breed in streams, which have high oxygen levels, have larvae with short gills. One of the most successful groups of salamanders are the Plethodontidae, the lungless salamanders. Most species of these salamanders live and breed on land, never entering water. They have no lungs, and oxygen uptake occurs primarily through the thin, porous skin. One requirement for this gaseous exchange is moisture, and these salamanders live primarily in damp, cool forests.
Life History of Salamanders and Newts
Primitive families of salamanders deposit eggs in water and have aquatic larvae. Other families of salamanders are unique among amphibians in producing a spermatophore for the transfer of sperm from the male to the female. The spermatophore is a gelatinous structure with a sperm cap resembling a tiny mushroom. The spermatophore is transferred from the male to the female in an elaborate courtship ritual. In some species, the male rubs secretions from a gland under his chin over the body of the female and entices her to follow him about. He then deposits a spermatophore on the substrate of the pond, which the female straddles and picks up with her cloaca. Fertilization is therefore internal in those species that produce a spermatophore. Lungless salamanders are active on the forest floor during moist or humid periods. Males are antagonistic to one another and appear to establish small territories that they defend from other males. The territorial encounters include biting and chasing and can result in injuries, including loss of part of the tail.
Defense Against Predators
Like other amphibians, salamanders and newts have toxic skin secretions produced by skin glands that are used in various ways as defense mechanisms to repel predators. In some species of newts, glands are concentrated on the dorsum, and when disturbed by a predator, the salamander displays an "unken reflex." This display includes bending the body in a U-shape and showing bright coloration of the underbelly. At the same time, the animal becomes immobile, thus decreasing the chance that a predator will attack. Other species have glands concentrated on the tail and engage in tail lashing or tail undulation. In tail lashing, the salamander violently whips its tail toward the predator, which attacks the tail and tastes the noxious secretions. In tail undulation, the body of the salamander remains immobile while the tail is waved in a sinuous fashion above the body. The tail in these species can be autotomized, or broken from the body by the salamander. Thus, if a predator attacks the waving tail, the salamander loses the tail but escapes with its life. Other species actively defend themselves if attacked by a predator. Amphiumas are large, powerful salamanders that live in ponds, swamps, or marshes in the southeast United States. Adults reach one meter in length and can inflict a painful bite with their sharp teeth. In a unique manner of defense, slender salamanders can secrete copious amounts of an adhesive substance from their glands. When attacked by a garter snake, the salamander's secretions glue the snake's body to itself, and it is unable to swallow the salamander.
Families: Ten families, including Ambystomatidae (mole salamanders), Amphiumidae (amphiumas), Cryptobranchidae (hellbender and giant salamanders), Dicamptodontidae (Pacific giant salamanders), Plethodontidae (lungless salamanders), Proteidae (waterdogs and mudpuppies), Rhyacotritonidae (torrent salamanders), Salamandridae (newts), Sirenidae (sirens)
Geographical location: Eurasia and North America, with one family extending into South America
Habitat: Many habitats, including forests, savannas, prairies, freshwater ponds and streams, and ephemeral pools
Gestational period: Varies among species; species that breed in ponds have larval stages that last two to six months, whereas the larval stage of stream-breeding species may last several years
Life span: Varies among species; larger species tend to live longer than smaller ones; large aquatic salamanders have lived for fifty to fiftyfive years in captivity
Special anatomy: Long body with long tail and four legs; some species are legless
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