Thorius dubitus Taylor 1941

This is a small species; adult standard length averages 19.8 mm in 10 males (range 18.2-21.7) and 20.6 mm in 10 females (range 18.1-22.0). The head is moderately wide; SL averages 7.2 times head width in males (range 6.2-8.7) and 7.6 times head width in females (range 7.0-8.3). Snouts are rounded to bluntly pointed. Nostrils are relatively large and elongate; the mean ratio of major axis to minor axis is 1.4 in males (range 1.2-1.6) and 1.5 in females (range 1.2-1.8). The eyes are somewhat protuberant and extend beyond the margin of the jaw in dorsal view, especially in males. A suborbital groove intersects the lip on each side of the head. The single cleared-and-stained specimen, a male, has two premaxillary teeth, six vomerine teeth, and no maxillary teeth. Limbs are relatively long; limb interval averages 3.5 mm in males (range 2.5-4) and 4.6 mm in females (range 4-5). Feet are relatively well developed. The middle two fingers and the middle three toes are much longer than the outer digits. Adjacent digits are free from one another only at their tips, which are rounded except in some smaller individuals in which they are slightly pointed. There are poorly developed subterminal pads on some of the larger specimens. The tail is relatively short and only rarely exceeds standard length; mean SL divided by tail length equals 1.23 in males (range 1.01-1.69) and 1.16 in females (range 0.99-1.32). The tail is round (in cross section) in smaller specimens, and quadrangular to somewhat laterally compressed in larger specimens. Coloration in life, based on field notes by J. Hanken for MVZ 182624-32: Most specimens have a greenish dorsal stripe (Hanken and Wake 1998).

Thorius dubitus is known only from the vicinity of the type locality near Puerto del Aire, which is ca. 3 km W of the village of Acultzingo, Veracruz, Mexico, very close to the Puebla border. Recorded elevations range from 2380 to 2475 m. The predominant vegetation type is pine-oak cloud forest, which is characteristic of these and other localities that lie along the southeastern edge of the Mexican plateau. Thorius dubitus is an exclusively terrestrial species. Salamanders are found under wood chips, under and inside logs, under the bark of logs, and under rocks. Thorius dubitus is sympatric with at least two congeners in the vicinity of Puerto del Aire: T. troglodytes, another exclusively terrestrial species; and T. magnipes, which is found both on the ground and in arboreal microhabitats. A third sympatric species may also be present, as a single specimen of T. spilogaster (KU 106818) is recorded from this locality. We have, however, examined hundreds of specimens of Thorius from this locality and others nearby and failed to identify other specimens of T. spilogaster; locality data for this specimen may be in error (Hanken and Wake 1998).

This taxon is found in the Sierra Madre de Oaxaca pine-oak forests, an ecoregion of northern Oaxaca, Mexico exhibiting a large number of endangered species, so that the conservation value is outstanding in terms of uniqueness of the habitat. The Sierra Madre de Oaxaca pine-oak forests is within the Tropical and Subtropical Conifer Forests biome, and the ecoregion is known for elevated plant endemism, especially within the Sierra de Juarez montane forests.

This ecoregion is located in northern Oaxaca State, and is delineated by the Sierra Norte de Oaxaca Mountains, which have characteristically abrupt and rugged topography. Its tallest peak is Zempoaltepetl (3400 metres), and most of the terrain in this area is above 1000 metres. Three mountain chains or sierras constitute the Sierra Madre de Oaxaca: Juarez, Aloapaneca and Zempoaltepec. The climate is temperate and humid with annual temperatures ranging from 16°C to 20°C. The annual mean precipitation varies greatly from 700 millimetres (mm) to as great as 4000 mm.

The forests also exhibit a high diversity of amphibians, including: the endemic Acultzingo Pigmy Salamander (Thorius dubitus EN), known only from the type locality near Puerto del Aire near Veracruz; the endemic Claw-toed False Brook Salamander (Pseudoeurycea unguidentis CR), known solely from Cerro San Felipe /Cerro San Luis in north-central Oaxaca; the endemic Lower Cerro Pygmy Salamander (Thorius pulmonaris EN), known only from Cerro San Felipe region, central Oaxaca; MacDougal's Pygmy Salamander (Thorius macdougalli VU); and the endemic Mexican Axolotl (Ambystoma mexicanum CR), found in Lakes Chalco and Xochimilco of the Valley of Mexico near Mexico City; the near-endemic Sierra Juarez Moss Salamander (Cryptotriton adelos EN); the endemic Schmidt's Pygmy Salamander (Thorius schmidti EN), known only from near the village of Zoquitlán in southern Puebla, Mexico; and the endemic Mustache False Brook Salamander (Pseudoeurycea mystax EN).

The Sierra Juarez Spiny Lizard (Sceloporus cryptus) is endemic to the ecoregion, and limited in range to drier parts of the Sierra de Juarez, in northeastern Oaxaca. There are a number of threatened reptilian taxa in the ecoregion including theRibbon Graceful Brown Snake (Rhadinaea fulvivittis VU), a limited distribution snake endemic to southern Mexico.

Avian taxa found here include the Dwarf Jay (Cyanolyca nana EN), Bearded Tree Quail (Dendrortyx barbatus CR), Tamaulipas Pygmy-owl (Glaucidium sanchezi) and Grey-barred Wren (Campylorhynchus megalopterus) as restricted-range bird species, which includes this ecoregion. The Oaxaca Sparrow (Aimophila notosticta NT), Golden-cheeked Warbler (Dendroica chrysoparia EN), Russet Nightingale-thrush (Catharus occidentalis), Hooded Yellowthroat (Geothlypis nelsoni), and Collared Towhee (Pipilo ocai) are also species which thrive in the habitats offered by this mountainous ecoregion.

This ecoregion presents a mosaic of vegetatative associations, due to the varied climate and topography. These formations include tropical evergreen forest, montane cloud forest, pine forest, pine-oak forest, and oak forest. The pine forests, at elevations between 1600 and 2600 metres (m), include trees that are 25 to 40 m tall. Dominant pine species are Mexican White Pine (Pinus ayacahuite); Lawson's Pine (P. lawsonii), a Mexican endemic; Chiapas White Pine (P. strobus var. chiapensischiapensis);Michoacan Pine (P. devoniana LR/LC) and Smooth-barked Mexican Pine (P. pseudostrobus). These pine forests have a robust understory and an herbacious layer dominated by numerous species of the Ericaceae family.

Thorius dubitus, commonly known as the Acultzingo pigmy salamander, is a species of salamander in the family Plethodontidae. It is endemic to Mexico where it is found in the Sierra Madre de Oaxaca of west-central Veracruz and adjacent Puebla. Its natural habitats are pine-oak cloud forests. It occurs under wood chips, logs, and rocks, and under the bark of logs and inside logs. It is threatened by habitat loss caused by logging, livestock, and subsistence agriculture.