ABSTRACT
Order Urodela (Caudata) of Class Amphibia contains three taxonomic suborders and ten families of living salamanders (Duellman and Trueb 1986; Larson and Dimmick 1993): suborder Cryptobranchoidea (Cryptobranchidae, Hynobiidae), suborder Salamandroidea (Ambystomatidae, Amphiumidae, Dicamptodontidae, Plethodontidae, Proteidae, Rhyacotritonidae, Salamandridae), and suborder Sirenoidea (Sirenidae). Urodela also includes some ta*a known only from fossils (Milner 2000; Carroll 2001; Gao and Shubin 2001), but this review is restricted to evaluating relationships among extant species of salamanders. The most stable taxonomic category in salamanders is the family; all families except Proteidae are reasonably well supported as monophyletic groups by morphological and molecular data. Family Proteidae is a tentative grouping of the genera Necturus and Proteus, which share an evolutionary derived chromosome number (Kezer et al. 1965; Hecht and Edwards 1976), and each of which is a monophyletic grouping of extant forms. Suborders Cryptobranchoidea and Sirenoidea receive strong support as monophyletic groups from numerous studies, but monophyly of suborder Salamandroidea is tentative. Internal fertilization is the strongest synapomorphy of suborder Salamandroidea, and combined analyses of molecular and morphological characters are compatible with monophyly of this group (Larson and Dimmick 1993). However, phylogenetic analyses of molecular data alone and of most morphological characters other than those of the
fertilization system do not support monophyly of Salamandroidea (Hillis 1991; Larson and Dimmick 1993).
