PlethodontidaeLungless Salamanders

By far the most spe­ciose and di­verse fam­ily of sala­man­ders, Pletho­d­on­ti­dae com­prises more than 250 species in ap­prox­i­mately 28 gen­era. Rep­re­sent­ing more than half of all known sala­man­der species, with new species being dis­cov­ered yearly, the lun­g­less sala­man­ders are found through­out the north­east­ern U.S., and on the west coast of North Amer­ica. One genus is known from South­ern Eu­rope. Pletho­d­on­tids have also ra­di­ated into trop­i­cal Amer­ica, with by far the great­est trop­i­cal dis­tri­b­u­tion of any sala­man­der fam­ily.

Pletho­d­on­tids are char­ac­ter­ized by a na­solabial groove that aids in chemore­cep­tion. All pletho­d­on­tids are also lun­g­less (lun­g­less­ness and re­duced lungs are in­de­pen­dently de­rived in the few other sala­man­der species show­ing this char­ac­ter). All adult pletho­d­on­tids have four limbs, with four dig­its on the fore­limbs. Sev­eral skele­tal char­ac­ters, in­clud­ing the loss of mul­ti­ple cra­nial bones, also di­ag­nose the group. There is, how­ever, such di­ver­sity within this fam­ily that it is dif­fi­cult to iden­tify com­mon traits by which the ca­sual ob­server might iden­tify a pletho­d­on­tid: body shape ranges from elon­gate and slen­der, to ro­bust. Tails range from body length, to twice body length. Pletho­d­on­ti­dae in­cludes both the small­est (30 mm total adult length in Tho­rius) and some of the largest (320 mm, Pseu­doeurycea) ter­res­trial sala­man­ders. Egg guard­ing is often per­formed by fe­males, and some­times by males. Diploid num­ber is 26 or 28. Adult pletho­d­on­tids in­clude aquatic and ter­res­trial forms. Neoteny is rec­og­nized in a few species (e.g. Eu­rycea, Ty­phlo­molge, and oth­ers in the tribe Hemi­dactyli­ini -- see below). These species live in caves or springs, and in ad­di­tion to in­com­plete meta­mor­pho­sis, often have de­gen­er­ate eyes and re­duced skin pig­men­ta­tion.

Pletho­d­on­ti­dae is com­monly split into two sub­fam­i­lies, Desmog­nathi­nae and Pletho­d­on­ti­nae, the lat­ter of which con­tains three tribes: Hemi­dactyli­ini, Pletho­d­onini, and Boli­toglossini. Desmog­nathines have a unique jaw-open­ing mech­a­nism in which the lower jaw is held sta­tion­ary while the skull swings up­ward. Desmog­nathines and Hemi­dactyli­ini dis­play in­di­rect de­vel­op­ment, while mem­bers of the other two pletho­d­on­tine tribes have di­rect de­vel­op­ment of ter­res­trial eggs. Found pri­mar­ily in the neotrop­ics, Boli­toglossini in­cludes nearly half of all ex­tant sala­man­der species, with many new species still being dis­cov­ered. Being lun­g­less, all pletho­d­on­tids must keep their skin wet to allow for cu­ta­neous res­pi­ra­tion. As such, trop­i­cal sala­man­ders such as boli­toglossines are typ­i­cally found in deep shade, in the pri­mary forests that are being cut, mean­ing that many species will prob­a­bly dis­ap­pear be­fore being dis­cov­ered and de­scribed. Sev­eral species of pletho­d­on­tids have been used in evo­lu­tion­ary re­search, es­pe­cially in stud­ies of the role of het­e­rochrony in gen­er­at­ing mor­pho­log­i­cal nov­el­ties.

Pletho­d­on­tids ap­pear to be dis­tantly re­lated to all of the other sala­man­der fam­i­lies that have in­ter­nal fer­til­iza­tion (Sala­man­droidea). They are prob­a­bly sis­ter to Am­phi­u­mi­dae, but this fam­ily, too, has no close liv­ing rel­a­tives.

Fos­sil pletho­d­on­tids are known from the Miocene through the Pleis­tocene in 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., D. Heyse, R. High­ton, and T. Jack­man. 1996. Pletho­d­on­ti­dae: Tree of Life. (Web­site) http://​tolweb.​org/​tree?​group=Plethodontidae&​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.

Wake, D. B. 1966. Com­par­a­tive os­te­ol­ogy and evo­lu­tion of the lun­g­less sala­man­ders, fam­ily Pletho­d­on­ti­dae. Mem­oirs of the South­ern Cal­i­for­nia Acad­emy of Sci­ences 4:1-111.

Zug, G. R. 1993. Her­petol­ogy: an in­tro­duc­tory bi­ol­ogy of am­phib­ians and rep­tiles. Aca­d­e­mic Press, San Diego.

Con­trib­u­tors

Heather Hey­ing (au­thor).

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

metamorphosis

A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.

motile

having the capacity to move from one place to another.