Three new species of minute salamanders (Thorius : Plethodontidae) from Guerrero, Mexico, including the report of a novel dental polymorphism in urodeles

Three new species of minute lungless salamanders of the Mexican genus Thori us (Plethodontidae) are described from montane forests in the Sierra Madre del Sur of Guerrero. Each species is distinguished from congeners by a comb ination of body size, external morphology, osteology, dental traits, and pr oteins. Thorius omiltemi and T. grandis are among the largest species withi n the genus; standard length (SL) approaches or exceeds 30 mm in many adult s. Thorius infernalis is much smaller (SL < 19 mm). Adult T. grandis displa y an extreme, unique sexual dimorphism involving the presence/absence of ma xillary teeth and several related features of cranial osteology. Protein (a llozyme) data for T. omiltemi and T. grandis reveal substantial levels of g enetic differentiation relative to species in Veracruz, Puebla, and Oaxaca. Comparable genetic data are unavailable for T. infernalis, The three speci es collectively define a broad elevational range, from high elevation T. om iltemi and T. grandis (2200-2700 m and 2495-3360 m, respectively) to lower montane T. infernalis (1140 m), Description of several additional species o f plethodontid salamanders from central montane Guerrero underscores the re gion's rich herpetological diversity, which includes many endemic species o f both amphibians and reptiles.