Abstract
We describe three new species of minute salamanders, genus Thorius, 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. Adult Thorius pinicola sp. nov., T. longicaudus sp. nov., and T. tlaxiacus sp. nov. are larger than T. minutissimus and possess elliptical rather than oval nostrils; T. pinicola and T. longicaudus also have longer tails. All three new species occur west of the range of T. minutissimus, which has the easternmost distribution of any member of the genus. The new species are distinguished from each other and from other named Thorius in 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 redescribe T. minutissimus and a related species, T. narisovalis, to further clarify the taxonomic status of Oaxacan populations and to facilitate future studies of the remaining genetically differentiated Thorius that 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. Thorius may be the most endangered genus of amphibians in the world. All species may go extinct before the end of this century.
Highlights
The smallest salamanders in Mexico, members of the family Plethodontidae, belong to the genus Thorius Cope, 1869
The additional key finding that enabled us to untangle the taxonomy of populations in southern Oaxaca was our rediscovery of topotypic T. minutissimus
The recently published molecular phylogeny for Thorius showed that T. minutissimus is both the sister taxon of T. narisovalis and well differentiated from T. longicaudus, T. pinicola and T. tlaxiacus (Rovito et al, 2013)
Summary
The smallest salamanders in Mexico, members of the family Plethodontidae, belong to the genus Thorius Cope, 1869. Taxonomy of Thorius has proven difficult because of their small size and general morphological similarity, especially externally, but once the taxa. How to cite this article Parra-Olea et al (2016), Biology of tiny animals: three new species of minute salamanders (Plethodontidae: Thorius) from Oaxaca, Mexico. Characters used to distinguish species in other plethodontid genera typically include the number of trunk vertebrae, external color pattern, numbers of premaxillary, maxillary or vomerine teeth, relative limb length, and characteristics of the manus, pes and digits. All Thorius, have 14 trunk vertebrae and reduced limbs, and in most species the digits are poorly formed and syndactylous and maxillary teeth are absent. It was difficult if not impossible to confidently associate names with most populations, and there was a general sense that many additional species remained undescribed
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