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By Heather Heying
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.
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http://tolweb.org/tree?group=Plethodontidae&contgroup=Caudata
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Contributors
Heather Heying (author).
