Description
Thorius infernalis is a small salamander species with a snout-vent length of 18.6 - 18.8mm. It has a pointed snout and a fairly broad head in comparison to the width of its body. The nostrils are ovate, and the eyes project slightly past the jaw when viewed from above. A groove underneath each eye extends to the lip. The limbs are short, and the feet and hands are narrow with fused digits and pointed digit tips. The relative lengths of the fingers are as follows, from longest to shortest: III > II > IV > I. The relative lengths of the toes are as follows, from longest to shortest: III > IV > II > V > I. The tail is stocky and narrows out at the end. There is a noticeable postiliac gland (Hanken et al 1999).

Thorius infernalis is distinguished from similar species in this genus by its relatively long tail in comparison to its small body size, shorter limbs, pointed toe tips with fused toes, and narrower head with a more pointed snout. It is differentiated from T. omiltemi and T. grandis, which are the other Thorius species found in Guerrero, Mexico, by its small size, and lack of maxillary teeth. When compared to T. minutissimus, T. infernalis can be differentiated by having less protuberant nostrils and lacking rounded toe tips. It is distinguished from T. pennatulus, T. narismagnus, and T. smithi, by lacking rounded nostrils (Hanken et al. 1999).

In life, the sides are fairly dark. A pale stripe runs from the back of the neck down to the tail, though it fades in color as it reaches the tail. The underside is lighter than the sides, and is noticeably lighter at the throat. In preservative, it is golden brown overall, though with darker sides and a lighter back and underside. A faint stripe runs from the head to the base of the tail. The throat is spotted white, with markings interspersed throughout the underside. Its irises are gray (Hanken et al 1999).

The male has one premaxillary tooth and five vomerine teeth, whereas the female lacks premaxillary teeth and has seven vomerine teeth (Hanken et al 1999).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico

View distribution map in BerkeleyMapper.

This species is known from a single location in Sierra Madre del Sur of central Guerrero, Mexico. It was found at a lower montane region with an elevation of 1140m. This species is believed to be predominantly terrestrial, occupying riparian habitats along hillsides in forested areas. The site where T. infernalis was found is near an area used for growing coffee, and much of the surrounding hillsides have been cleared of undergrowth (Hanken et al. 1999).

Life History, Abundance, Activity, and Special Behaviors
Little is known about this species. Thorius infernalis is only known from 2 individuals collected in the late 1970s. Like other plethodontid salamanders, it is lungless and breathes through its skin. It is presumably terrestrial and displays direct development (Parra-Olea et al. 2014, Wake and Hanken 1996).

Trends and Threats
This species may be extinct as a result of habitat loss and degradation. The site where T. infernalis was known to occur, near Atoyac, is primarily used for coffee cultivation. Further human encroachment on suitable habitat continues to decrease the area in which this species is likely to be found. The small body and limb size of T. infernalis suggests that they disperse short distances. Therefore, loss of suitable habitat may eradicate the population in that area (Ochoa-Ochoa et al. 2009, Parra-Olea et al. 2014, Rovito et al. 2013).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Loss of genetic diversity from small population phenomena

Comments
The species authority is: Hanken, J., Wake, D. B., Freeman, H. L. (1999). "Three New Species of Minute Salamanders (Thorius: Plethodontidae) from Guerrero, México, Including the Report of a Novel Dental Polymorphism in Urodeles." Copeia, 1999(4), 917-931.

As there are only two known specimens to represent this species, no molecular analysis has been conducted to genetically compare this species to others. However, Thorius species can be grouped by the presence of maxillary teeth, which T. infernalis lacks. This absence of maxillary teeth is thought to represent an ancestral trait among the genus, suggesting that T. infernalis is a more ancestral species within Thorius (Hanken et al. 1999, Rovito et al. 2013).

The species epithet, infernalis, is derived from Latin meaning “of the lower world” and refers to the lower elevation in which this species was found. Its common name refers to the nearby city of Atoyac de Álvarez, which is among the hottest geographical locations in North America (Hanken et al. 1999).

Further surveys are needed to determine if this species still exists in the wild. Field verification is needed to better predict potential distributional ranges in order to effectively protect land that is suitable for T. infernalis in hopes of saving the species (Ochoa-Ochoa et al. 2009).

References

Hanken, J., Wake, D. B., Freeman, H. L. (1999). ''Three New Species of Minute Salamanders (Thorius: Plethodontidae) from Guerrero, México, Including the Report of a Novel Dental Polymorphism in Urodeles.'' Copeia, 1999(4), 917-931.

Ochoa-Ochoa, L., Urbina-Cardona, J. N., Vázquez, L.-B., Flores-Villela, O., and Bezaury-Creel, J. (2009). ''The effects of governmental protected areas and social initiatives for land protection on the conservation of Mexican amphibians.'' PLoS One, 4(9), e6878.

Parra-Olea, G., Wake, D., García-París, M., Hanken, J. (2008). Thorius infernalis. The IUCN Red List of Threatened Species. Version 2014.3. www.iucnredlist.org. Downloaded on 22 March 2015.

Rovito, S. M., Parra-Olea, G., Hanken, J., Bonett, R. M., Wake, D. B. (2013). ''Adaptive radiation in miniature: the minute salamanders of the Mexican highlands (Amphibia: Plethodontidae: Thorius).'' Biological Journal of the Linnean Society, 109, 622-643.

Wake, D. B., Hanken, J. (1996). "Direct development in the lungless salamanders: what are the consequences for developmental biology, evolution, and phylogenesis?" International Journal of Developmental Biology, 40, 859-869. [link]

Species Account Citation: AmphibiaWeb 2015 Thorius infernalis: Atoyac Minute Salamander <https://amphibiaweb.org/species/5358> University of California, Berkeley, CA, USA. Accessed Dec 26, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Dec 2024.

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