AmphibiaWeb - Thorius adelos
Thorius adelos
Sierra Juarez Hidden Salamander, Sierra Juarez Moss Salamander
family: Plethodontidae
subfamily: Hemidactyliinae
Taxonomic Notes: This is a small species known from fewer than 10 individuals. It has not been seen for many years, but the habitat in which it occurred is intact. It was originally placed in Nototriton, but when that taxon was subdivided by Garcia-Paris and Wake (2000, Copeia) it ended up in a new genus Cryptotriton. What made this assignment problematic was the fact that adelos was the only member of the genus north/west of the Isthmus of Tehuantepec. Wake, Rovito, Maisano and Hanken (2012, Zootaxa) studied ct scans of the skeleton of a specimen and concluded that adelos is a member of Thorius, despite the fact that it lacks the subocular groove, present in all other species of Thorius. Several unique osteological features demonstrate that it is in the Thorius clade and should be assigned to that genus. These include the presence of a large dorsal fonatanelle in the skull and a columnar posterior process of the squamosal (see for osteological features).

© 2010 Sean Michael Rovito (1 of 3)
Conservation Status (definitions)
IUCN (Red List) Status Near Threatened (NT)
National Status None
Regional Status None
Access Conservation Needs Assessment Report.



View distribution map in BerkeleyMapper.


Thorius adelos is small and rare species of minute salamanders with a holotype snout vent length of 21.1 mm and a distance from the axilla to the groin measuring 11.5 mm. The salamander is only known from four specimens (Papenfuss and Wake 1987, Parra-Olea et al. 2008). This salamander has a rounded snout and upward-tilted nostrils. Thorius adelos has unique nasolabial grooves that extend from the back of the nostrils to the lip. Thorius adelos also has suborbital grooves that start below the eye and ends posterior to the eye but does not intersect with the lip. The eyes are average sized for this species and bulge out beyond the jaw from the dorsal view. The head of the holotype is 3.1 mm in width and the length of the snout to gular fold is 3.9 mm. The forelimbs are 3.8 mm long, and hind limbs are 4.7 mm. The limbs are separated by four costal grooves. The hands and feet are small. On each hand, fingers I and II are fused together and so are III and IV. The tips of the II and III digits on the hand are free. The right foot is 1.2 mm in width, and toes I and II are fused together, as well as the IV and V but the tips of II, III and IV are separated. There are concave disks on the hands and feet. Thorius adelos also has distinct costal folds that go from the side of the middorsal line to the abdomen of the species and a short tail, 25.1 mm, that gradually thins out (Papenfuss and Wake 1987).

At the time of its description T. adelos was thought to be a member of Nototriton. Since then, the species within Nototriton have been split into at least three genera, Nototriton, Ctryptotriton, and Thorius. Nototriton and Thorius both have fused paired frontal processes of the unpaired premaxillary bone at the base and lack vomerine processes at the back of the eye. In contrast to members of Cryptotriton, T. adelos, does not have pierced nasal bones with nasolacrimal duct. More specifically, by its short tail, having a tail proportion that is 1.05 - 1.19 the length of the snout vent length, differentiates T. adelos from Nototriton barbouri (0.94 - 1.13), Nototriton richardi (1.25 - 1.36), and Cryptotriton veraepacis (1.46). Thorius adelos also has more narrow feet (0.06 times the snout-vent length) than Cryptotriton alvarezdeltorol (0.08), Cryptotriton nasalis (0.09), and C. veraepacis (0.09). Thorius adelos has a more moderate nostril diameter (0.016 – 0.019 times the snout-vent length) when compared to C. alvarezdeltorol (0.024 - 0.026), N. barbouri (0.010 - 0.011), C. nasalis (0.024), N. picadoi (0.007), and C. veraepacis (0.017). Thorius adelos also has a more moderate combined limb length (0.40 – 0.45 times the snout-vent length) compared to N. barbouri (0.32 - 0.35), C. nasalis (0.51), N. picadoi (0.35), N. richardi (0.33 - 0.37), and C. veraepacis (0.52) (Papenfuss and Wake 1987).

From other members of the Thorius genus, the skull of T. adelos is more robust and is more extensively ossified than all other known Thorius. Additionally, the fontanelle is smaller and the skull is shorter and more compact in T. adelos than in most Thorius. Thorius adelos also has a posteriorly directed columnar process or "spur" on the posterior margin of the squamosal bone, which is only present in Thorius and Oedipina (Wake 1966). Thorius adelos has larger sized maxillary teeth as well as more maxillary teeth (26) in number than any other Thorius. Lastly, the condyle is less evident and less developed in Thorius adelos than other Thorius species (Wake et al. 2012).

In preservation, the back of the head, body, and tail are brown. Thorius adelos has a tan-fluorescent pigment that appears in a veil-form along the head, body, and tail. There is a cream-colored stripe on dorsolateral side of T. adelos that starts from the back of the head, above the gular fold, curving in towards the middle of its back, and then dorsolaterally onto the sides until it suddenly ends at the second costal groove. Dorsal to these stripes is a dark brown stripe that extends from the second costal groove, along the side of the body and neck, and then just before the gular fold, it curves upward on to the dorsolateral edge of the head and continues over the eye to the anterior margin of the eye. The sides of the body are a darker brown than its back. This contrast in color gives an appearance of a lighter brown stripe on the back. The ventral side of T. adelos is light brown with scattered cream-colored spots on its tail and belly. The chin has irregular light brown spots and the limbs are light brown with scattered cream dots (Papenfuss and Wake 1987).

Specimens are similar in coloration and only vary slightly (Papenfuss and Wake 1987).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico


View distribution map in BerkeleyMapper.

Thorius adelos is known only from its type locality, which is 3.7 miles (6.1 km) south of Puerto del Viento on the Caribbean Escarpment of the Mesa Central of Chiapas, Mexico. Thorius adelos was found in the humid cloud forest of the Caribbean slopes of Sierra de Juarez, Mexico at 1530 - 2050 m elevation. Specimens were found 65 km northeast of Guelatao, Oaxaca, Mexico inside arboreal bromeliads (Papenfuss and Wake 1987).

Life History, Abundance, Activity, and Special Behaviors

The relative abundance of T. adelos appears to be very small and despite being sought after, only one specimen was found after the initial three were found (Parra-Olea et al. 2008).

Trends and Threats

The forest habitat of T. adelos has been extremely disturbed and reduced, in part due to the 1990s fires in Cerro Baul (Parra-Olea et al. 2008). Most of the cloud forest has been deforested for agriculture and human use, leaving only small portions remaining (Papenfuss and Wake 1987).

Thorius adelos was originally listed as “Endangered” by IUCN Redlist. It is not found in protected areas, making it necessary to maintain the remaining portions of cloud forest. Further conservation efforts are need for both land and water protection (Parra-Olea et al. 2008).

Possible reasons for amphibian decline

General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Secondary succession
Habitat fragmentation

Originally T. adelos was described as Nototriton adelos on the basis of morphology (Papenfuss and Wake 1987), but this was problematic because, as the only member from west of the Isthmus of Tehuantepec in southeastern Mexico, T. adelos was geographically isolated from other members of its genus. Paraphyly of Nototriton was proven by DNA sequencing of cyt b gene 16S ribosomal subunit gene (rDNA). Nototriton adelos was then categorized as Cryptotriton but it was again zoogeographical isolated. Unfortunately, there was insufficient genetic material to further analyze T. adelos specifically (García-París and Wake 2000). Later efforts to collect more T. adelos specimens were fruitless. This made further DNA analysis of the species impossible because of the limited number and age of specimens. Osteology was then used instead to determine the genus change from Cryptotriton adelos to Thorius adelos (Wake et al. 2012).

The species epithet comes from the Greek word "adelos”, which means “unseen or obscure” and references the species having been overlooked and its relative obscurity (Papenfuss and Wake 1987).

The common name for is T. adelos is the “Sierra Juarez hidden salamander”, or “Sierra Juarez moss salamander”. It gets its nickname from the rarity and locality of this species (Liner and Casas-Andreu 2008).


García-París, M., and Wake, D. B. (2000). “Molecular phylogenetic analysis of relationships of the tropical salamander genera Oedipina and Nototriton, with descriptions of a new genus and three new species.” Copeia 2000, 42-70.

Papenfuss T.J, Wake D.B. (1987). ''Two new species of plethodontid salamanders (genus Nototriton) from Mexico.'' Acta Zoologica Mexicana Nueva Serie, 21, 1-16.

Parra-Olea, G., Wake, D., Hanken, J. (2008). ''Thorius adelos.'' The IUCN Red List of Threatened Species 2008: e.T59233A11904017. Downloaded on 13 November 2018.

Wake D.B., Rovito S.M., Maisano J.A., Hanken J. (2012). ''Taxonomic status of the enigmatic salamander Cryptotriton adelos (Amphibia: Plethodontidae) from northern Oaxaca, Mexico, with observations on its skull and postcranial skeleton.'' Zootaxa, 3579, 67–70.

Originally submitted by: Aileen Lavelle and Karla Aguilar (first posted 2018-11-26)
Description by: Michelle S. Koo (updated 2021-04-22)
Trends and threats by: Michelle S. Koo (updated 2021-04-22)
Comments by: Michelle S. Koo (updated 2021-04-22)

Edited by: Ann T. Chang (2021-04-22)

Species Account Citation: AmphibiaWeb 2021 Thorius adelos: Sierra Juarez Hidden Salamander <> University of California, Berkeley, CA, USA. Accessed Sep 24, 2021.

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Citation: AmphibiaWeb. 2021. <> University of California, Berkeley, CA, USA. Accessed 24 Sep 2021.

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