By Heather Heying
Approximately 30 extant species in a single genus are recognized in this family of secretive, burrowing salamanders. The family is widespread in North America, but not found on any other continents. They are known from Southeast Alaska and Labrador through the Southern edge of the Mexican plateau.
Ambystomatids are stout-bodied salamanders of moderate size (10-30 cm adult length). Their tails are thick, their limbs robust, their skin smooth and shiny, and many have bright color patterns. They exhibit the most derived pattern of spinal nerves known in salamanders, and their diploid number is 28. Most species have a diphasic life history, with aquatic larvae and fully metamorphosed terrestrial adults. Some species are obligately neotenic, and a few others are facultatively so, retaining larval features and an aquatic habit as adults. The axolotl, Ambystoma mexicanum, is a neotenic species in which metamorphosis can be experimentally induced, and it has been used extensively in embryological research. Two species (Ambystoma platineum and Ambystoma tremblayi) are gynogenetic triploids, each containing two sets of chromosomes from one parent species, and one set from the other. Females "mate" with males of the parent species that supplied two sets of chromosomes, but the sperm makes no genetic contribution to the offspring.
Ambystomatids are called mole salamanders for their tendency to live under litter or in burrows, emerging and returning to water only to breed. Among sexual species, courtship and breeding tends to occur in ponds in the Spring (although at least one species deposits eggs on land in the Fall, which is accompanied by egg guarding by females). During early Spring, some mole salamanders are known for their mass migrations to breeding sites, converging in very large numbers on ponds over the course of two or three days. Nuptial dances precede the deposition of numerous spermatophores by each male. Females pick up these sperm packets, and lay up to 200 eggs in the water over the course of several days.
Mole salamanders are members of the suborder Salamandroidea, the "advanced salamanders" that include all internally-fertilizing salamanders. Recently, the genera Dicamptodon and Rhyacotriton were removed from Ambystomatidae. Of the two resultant families, Dicamptodontidae is sister to the ambystomatids, while Rhyacotritonidae is probably basal among the Salamandroidea. Past analyses have placed the ambystomatids sister to Plethodontidae due to shared osteological characters and spinal nerve pattern. Most current analyses suggest instead that the Ambystomatidae-Dicamptodontidae clade is sister to Salamandridae. Historically, the genus Rhyacosiredon has been recognized in the Ambystomatidae, but its presence makes Ambystoma paraphyletic, so has been abandoned by most researchers.
Fossil ambystomatids are known from the upper Pliocene (extinct genus Amphitriton). Fossils of the extant genus Ambystoma are also known from the lower Oligocene through the Pleistocene of North America.
Adler, K., and T. R. Halliday, editors. 1986. Reptiles and Amphibians. Torstar Books Inc., New York.
Cogger, H. G., and R. G. Zweifel, editors. 1998. Encyclopedia of Reptiles and Amphibians, 2nd edition. Academic Press, San Diego.
Duellman, W. E., and L. Trueb. 1986. Biology of Amphibians. Johns Hopkins University Press, Baltimore, MD.
Larson, A., S. Damian, D. Heyse, T. Jackman, D. Maddison, and C. Phillips. 2001. Ambystomatidae: Tree of Life. 
http://tolweb.org/tree?group=Ambystomatidae&contgroup=Caudata
Pough, F. H., R. M. Andrews, J. E. Cadle, M. L. Crump, A. H. Savitzky, and K. D. Wells. 1998. Herpetology. Prentice-Hall, Inc., Upper Saddle River, NJ.
Zug, G. R. 1993. Herpetology: an introductory biology of amphibians and reptiles. Academic Press, San Diego.
Contributors
Heather Heying (author).
