Biology of tiny animals: three new species of minute salamanders (Plethodontidae:Thorius) from Oaxaca, Mexico

Abstract

We describe three new species of minute salamanders, genusThorius, from the Sierra Madre del Sur of Oaxaca, Mexico. Until now only a single species,T. minutissimus, has been reported from this region, although molecular data have long shown extensive genetic differentiation among geographically disjunct populations. AdultThorius pinicolasp. nov.,T. longicaudussp. nov., andT. tlaxiacussp. nov. are larger thanT. minutissimusand possess elliptical rather than oval nostrils;T. pinicolaandT. longicaudusalso have longer tails. All three new species occur west of the range ofT. minutissimus, which has the easternmost distribution of any member of the genus. The new species are distinguished from each other and from other namedThoriusin Oaxaca by a combination of adult body size, external morphology and osteology, and by protein characters (allozymes) and differences in DNA sequences. In addition, we redescribeT. minutissimusand a related species,T. narisovalis, to further clarify the taxonomic status of Oaxacan populations and to facilitate future studies of the remaining genetically differentiatedThoriusthat cannot be satisfactorily assigned to any named species. Populations of all five species considered here appear to have declined dramatically over the last one or two decades and live specimens are difficult to find in nature.Thoriusmay be the most endangered genus of amphibians in the world. All species may go extinct before the end of this century.