AMPHIBIAWEB
Thorius smithi
Smith's minute salamander
family: Plethodontidae
subfamily: Hemidactyliinae

© 2010 Sean Michael Rovito (1 of 3)
Conservation Status (definitions)
IUCN (Red List) Status Critically Endangered (CR)
CITES No CITES Listing
Other International Status None
National Status None
Regional Status None

 

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Description
Thorius smithi is a small and slender species in the Plethodontidae family. The two only known specimens, both females, are 20.3 and 20.4 mm in standard length. Its head is narrow, with a slightly truncated and bluntly pointed snout. The nostrils are relatively large and round to slightly elongate. It has nasolabial grooves extending through a cutaneous enlargement with only a slight ventral lobe. The eyes are moderately sized and when viewed from above, and project only slightly past the margin of the jaw. A suborbital groove found beneath the eyes meets the lip below the posterior margin of the orbit. The limbs are relatively long while the hands and feet are quite small. The longest digits have pointed tips but the outermost digits can barely be distinguished and do not have free tips. In order of decreasing length, the fingers are 3 > 2 > 1 > 4 and the toes are 3 > 2 > 4 > 1 > 5. It has a postiliac gland, but it is pale and obscure. It has a fairly long and slim tail, which gradually tapers to a pointed tip (Hanken and Wake 1994).

Unlike most of its close relatives, T. smithi has maxillary teeth. Three other species of Thorius also contain maxillary teeth, T. aureus, T. schmidti, and T. maxillabrochus, but they are much larger and none of them are sympatric with T. smithi. In addition, T. aureus has a much lighter ventral coloration, T. schmidti has less rounded nostrils, and T. maxillabrochus has wider feet and more rounded toe tips. Thorius insperatus, which is the only member of the genus Thorius sympatric with T. smithi, does not have maxillary teeth and has rounded, rather than pointed, toe tips. Other members of the genus may also bear some resemblance to the species. Thorius smithi can be distinguished from its congeners in the Sierra de Juárez - T. macdougalli, T. arboreus, and T. boreas - by its more rounded nostril, smaller size, and the presence of maxillary teeth (Hanken and Wake 1994).

In life, it is a rich dark brown, with an obscure, dull, faint dorsal stripe extending from near the eyes onto the tail. The sides of the stripe have a dark dorsolateral band that also extends onto the tail. The flanks and venter of this species are lighter and have copious white spots (0.1 - 0.2 mm in diameter), which are especially numerous by the throat. The limbs have some white spots as well, and match the rich brown of the flanks. The iris is charcoal colored (Hanken and Wake 1994).

This species has only been described from two specimens. In one of the specimens, the tail length exceeded the body length. Due to the small number of specimens studied, there is no other information on variation within the species (Hanken and Wake 1994).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico

 

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This species is known only from the Sierra de Juárez in northern Oaxaca, southwest of Vista Hermosa and Metates towns. It has been found at lower elevations than any other species of Thorius. The two specimens collected were found in cloud forest and tropical forest localities along Highway 175 between approximately 800 m and 1550 m. The holotype was found in a pile of wood chips and the paratype was found under a rock. The species may have a greater distribution than is known (Hanken and Wake 1994, Parra-Olea et al. 2008).

Life History, Abundance, Activity, and Special Behaviors
Reproduction is thought to be by direct development (Parra-Olea et al. 2008).

Trends and Threats
The greatest threat to T. smithi is likely habitat loss due to the destruction of forest for logging and agricultural use. Population trends are unknown. It has been recorded only twice at two different locations, and despite numerous attempts to locate it, the species is quite rare and possibly extinct (Parra-Olea et al. 2008).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities

Comments
The species authority is: Hanken, J., Wake, D. B. (1994). "Five new species of minute salamanders, genus Thorius (Caudata: Plethodontidae), from Northern Oaxaca, Mexico." Copeia, 1994(3), 573-590.

No biochemical analyses have been performed to determine the phylogenetic relationship of T. smithi to other Thorius species (Hanken and Wake 1994).

The species epithet, smithi, is derived from H. M. Smith, who contributed greatly to Mexican herpetology, including the taxonomy of Thorius (Hanken and Wake 1994).

Thorius salamanders are extremely hard to distinguish morphologically by virtue of their very small size, and in many instances, can only be accurately distinguished through biochemical data (Hanken and Wake 1994).

References

Hanken, J., Wake, D. B. (1994). ''Five new species of minute salamanders, genus Thorius (Caudata: Plethodontidae), from Northern Oaxaca, Mexico.'' Copeia, 1994(3), 573-590.

Parra-Olea, G., Wake, D. B., Hanken, J. (2008). Thorius smithi. The IUCN Red List of Threatened Species. Version 2014.3. www.iucnredlist.org. Downloaded in March 2015.



Written by Alicia Beattie (alicia.beattie AT siu.edu), Southern Illinois University, Carbondale
First submitted 2015-06-24
Edited by Gordon Lau (2015-07-06)

Species Account Citation: AmphibiaWeb 2015 Thorius smithi: Smith's minute salamander <http://amphibiaweb.org/species/4214> University of California, Berkeley, CA, USA. Accessed Oct 22, 2017.



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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Oct 2017.

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