Imperiled Amphibians and Reptiles - Amphibians

Amphibians are vertebrate animals in the taxonomic class Amphibia. They represent the most ancient group of terrestrial vertebrates. The earliest amphibians are known from fossils and date from the early Devonian era, some 400 million years ago. The three groups of amphibians that have survived to the present day are salamanders, frogs (and toads), and caecilians.

Salamanders belong to the orders Caudata or Urodela. They have moist smooth skin, slender bodies, four short legs, and long tails. This category includes the amphibians commonly known as newts (land-dwelling salamanders) and sirens (salamanders with lungs in addition to gills). The majority of salamanders are fairly small in size, most often six inches long or less. The Chinese and Japanese giant salamanders, which grow to be as large as five feet in length, are the largest of all amphibians. There are approximately 500 salamander species worldwide, and about 150 species in the United States.

Frogs and toads are in the order Anura. These amphibians do not have tails as adults. They have small bodies with two short front legs and two long hind legs. Their feet are webbed, and they are good jumpers and hoppers. True frogs belong to the family Ranidae, while true toads belong to the family Bufonidae. There are many other families in this order whose members are commonly described as tree frogs, tailed frogs, spadefoot toads, horned toads, clawed frogs, Surinam toads, narrow-mouth frogs, or poison dart toads. Many of the species go through a swimming tadpole stage before metamorphosing into an adult. However, in some species, eggs hatch directly as juvenile froglets, which are miniature versions of the adults. Tadpoles are most often herbivorous, although there are some carnivorous tadpoles, including cannibalistic species. Adults are carnivorous and catch prey with their sticky tongues. There are at least 5,000 known frog and toad species, but only about 100 of these species are found in the United States.

Caecilians belong to the orders Gymnophiona or Apoda and share a common ancestor with the other amphibians, but look much different. They are often mistaken for worms or snakes. They have long slender bodies with no limbs and are found primarily in the tropics. There are approximately 160 species of Caecilians worldwide, but none are native to the United States.

"Amphi-" means "both," and amphibians get their name from the fact that many species occupy both aquatic and terrestrial habitats. In particular, a large number of amphibian species undergo a dramatic change called metamorphosis, in which individuals move from an aquatic larval stage to a terrestrial adult stage. In many frog species, for example, aquatic, swimming tadpoles metamorphose into terrestrial jumping frogs. In the process, they lose their muscular swimming tails and acquire TABLE 7.1 Endangered and threatened amphibian species in the United States, March 2006 Adapted from "Listed FWS/Joint FWS and NMFS Species and Populations with Recovery Plans (Sorted by Listed Entity)" and "Listed U.S. Species by Taxonomic Group," in Threatened and Endangered Species System (TESS), U.S. Department of the Interior, U.S. Fish and Wildlife Service, March 6, 2006, http://ecos.fws.gov/tess_public/SpeciesRecovery.do?sort=1 and http://ecos.fws.gov/tess_public/SpeciesReport.do?kingdom=I&listingType=L (accessed March 6, 2006)forelimbs and hind limbs. Many amphibian species occupy terrestrial habitats through most of the year, but migrate to ponds to breed. However, there are also species that are either entirely aquatic or entirely terrestrial. Whatever their habitat, amphibians generally require some moisture to survive. This is because amphibians pass some oxygen and other chemicals in and out of their body directly through their living skin, using processes that require water to function.

TABLE 7.1
Endangered and threatened amphibian species in the United States, March 2006
Common name	Scientific name	Statusa	Recovery plan date	Recovery plan statusb
aE = endangered, T = threatened.
bRecovery plan stages: F = final, RD = draft under revision, RF = final revision.
SOURCE: Adapted from "Listed FWS/Joint FWS and NMFS Species and Populations with Recovery Plans (Sorted by Listed Entity)" and "Listed U.S. Species by Taxonomic Group," in Threatened and Endangered Species System (TESS), U.S. Department of the Interior, U.S. Fish and Wildlife Service, March 6, 2006, http://ecos.fws.gov/tess_public/SpeciesRecovery.do?sort=1 and http://ecos.fws.gov/tess_public/SpeciesReport.do?kingdom=I&listingType=L (accessed March 6, 2006)
Coqui, golden	Eleutherodactylus jasperi	T	4/19/84	F
Frog, California red-legged (subspecies range clarified)	Rana aurora draytonii	T	5/28/02	F
Frog, Chiricahua leopard	Rana chiricahuensis	T	None	—
Frog, Mississippi gopher	Rana capito sevosa	E	None	—
Frog, mountain yellow-legged	Rana muscosa	E	None	—
Guajon	Eleutherodactylus cooki	T	9/24/04	F
Salamander, Barton Springs	Eurycea sosorum	E	9/21/05	F
Salamander, California tiger	Ambystoma californiense	E, T	None	—
Salamander, Cheat Mountain	Plethodon nettingi	T	7/25/91	F
Salamander, desert slender	Batrachoseps aridus	E	8/12/82	F
Salamander, flatwoods	Ambystoma cingulatum	T	None	—
Salamander, Red Hills	Phaeognathus hubrichti	T	11/23/83	F
Salamander, San Marcos	Eurycea nana	T	2/14/96	RF(1)
Salamander, Santa Cruz long-toed	Ambystoma macrodactylum croceum	E	7/2/99	RD(2)
Salamander, Shenandoah	Plethodon shenandoah	E	9/29/94	F
Salamander, Sonora tiger	Ambystoma tigrinum stebbinsi	E	9/24/02	F
Salamander, Texas blind	Typhlomolge rathbuni	E	2/14/96	RF(1)
Toad, Arroyo (= arroyo southwestern)	Bufo californicus (= microscaphus)	E	7/24/99	F
Toad, Houston	Bufo houstonensis	E	9/17/84	F
Toad, Puerto Rican crested	Peltophryne lemur	T	8/7/92	F
Toad, Wyoming	Bufo baxteri (= hemiophrys)	E	9/11/91	F

A large number of amphibian species are in serious decline due 1to factors such as habitat loss, pollution, and climate change. Amphibians are particularly vulnerable to pollution because their skin readily absorbs water and other substances from the environment. For this reason, amphibians are frequently considered biological indicator species, meaning that their presence, condition, and numbers are monitored as a gauge of the overall well-being of their habitat.