Description
Pseudoeurycea obesa is a poorly-known species of lungless salamander with a robust (rounded) morphology that was described from one adult male and three juveniles. The snout-vent length of the male holotype measures 58.2 mm. The head is relatively wide and of medium length (respectively 17% and 24% of the snout-vent length), with a pitted dorsal surface, dorsally placed eyes, and a rather long and pointed snout. A mental gland is visible. The neck is poorly defined, and the species has no apparent paratoid glands. The limbs are stout and short (their combined length equaling ~42% of the snout-vent length), with broad hands and feet that show highly pointed digits. The tail is relatively short (70% of the snout-vent length ) and strongly tapered, constricted at the base, and with glandular ridges converging on the dorsal side (Parra-Olea et al. 2005).

Pseudoeurycea obesa is characterized by its robust body, the presence of two glandular ridges that are yellow-brown in color, situated dorsolaterally around the pelvis and the base of the tail. It is further identified by a distinct light-yellow coloration on the distal one-third of the tail, which contrasts with its darker grey-brown dorsum and tail base. The flanks of the body are slightly paler and mottled, while the posterior side of the limb base shows reddish marks. The species differs from closely related species P. werleri and P. mystax by its more robust body shape and the distinct yellow-brown glandular ridges around the pelvic region and tail base. It is further distinguished from congeneric species by the shape and coloration of its tail: stout and strongly tapered, and pale-yellow at the terminal third (also see sections above and below) (Parra-Olea et al. 2005).

In life, the coloration is brown-gray on the head to slate gray on the dorsum. The dorsum is marbled with brown and rusty areas. The rusty areas that are situated mid-dorsally are bigger around the nape and pelvis. The dorsal side of the body and the tail show black spots of variable sizes that are larger and more oval-shaped on the tail. Smaller blue-silver dots are densely represented on the limbs and the lateral sides, and more sparsely found on the dorsum and head. The glandular ridges are yellow-brown, and the base of the limbs show rusty-orange patches on the posterior side. The tail is dark brown anteriorly, morphing into its distinctive light-yellow coloration at the distal end. The iris has a reddish-brown base color with a reticulated pattern of dark brown (Parra-Olea et al. 2005).

Juveniles are noted to be similar in coloration but exhibit fewer black dorsal spots (Parra-Olea et al. 2005).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Mexico

View distribution map in BerkeleyMapper.

Pseudoeurycea obesa is only known from its type locality near Plan de Guadalupe, in the Sierra Mazateca (part of the wider Sierra Madre de Oaxaca), Oaxaca, Mexico (Parra-Olea et al. 2005; Johnson et al. 2017; Mata-Silva et al. 2021). Here, it occurs at high elevations (2150 - 2155 m elevation) near cloud forest remnants dominated by oak (Quercus), where it was found under rocks and schist slabs (Parra-Olea et al. 2005).

Life History, Abundance, Activity, and Special Behaviors
Virtually unknown. Individuals were noted to be slow moving when disturbed (Parra-Olea et al. 2005).

Larva
The species is presumed to be direct-developing (without a larval stage).

Trends and Threats
Pseudoeurycea obesa is classified as "Critically Endangered" by the IUCN Red List. The sole locality from which the species is known is situated amongst degraded cloud forest fragments that continue to be deforested. Its discovery in this altered habitat and under rocks among road-side talus could suggest a degree of resilience to habitat alteration, but population trends and its long-term tolerance to ongoing pressures remain unknown (IUCN 2016).

The species was given an Environmental Vulnerability Score of 18 (out of 19) based on its highly confined distribution and the degree of specialization of its putative reproductive mode, suggesting a very high vulnerability to environmental degradation (Wilson et al. 2013; Johnson et al. 2017). In the absence of demographic data, model predictions incorporating life-history traits and environmental threat levels suggest that P. obesa is most likely decreasing (Quintero et al. 2014).

Relation to Humans
There are no records on human use of the species.

Possible reasons for amphibian decline

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

Comments
Pseudoeurycea obesa is part of the wider P. leprosa group. In a phylogenetic analysis based on both mitochondrial genome fragments and several nuclear loci, P. obesa was consistently recovered as the sister taxon to P. werleri. Based on the concatenated data, these two species were in turn placed as sister taxa to a clade consisting of P. orchileucos and P. orchimelas (Rovito et al. 2015). Using a denser taxon coverage, a more recent analysis based on only two mitochondrial loci indicated that P. obesa and P. werleri are most closely related to P. mystax and P. conanti (Cázares-Hernández et al. 2022).

References
Cázares-Hernández, E., Jimeno-Sevilla, H.D., Rovito, S.M., López-Luna, M.A., and Canseco-Márquez, L. (2022). A new arboreal Pseudoeurycea (Caudata: Plethodontidae) from the Sierra de Zongolica, Veracruz, Mexico. Vertebrate Zoology, 72, 937–950. [link]

IUCN SSC Amphibian Specialist Group. (2016) Pseudoeurycea obesa. The IUCN Red List of Threatened Species 2016: e.T61909A53989532. https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T61909A53989532.en. Accessed on 23 November 2023.

Johnson, J. D., Wilson L.D., Mata-Silva V., García-Padilla E., and DeSantis, D.L. (2017). The endemic herpetofauna of Mexico: organisms of global significance in severe peril. Mesoamerican Herpetology, 4, 544–620. [link]

Mata-Silva, V., García-Padilla, E., Rocha, A., DeSantis, D.L., Johnson, J.D., Ramírez-Bautista, A., and Wilson, L.D. (2021). A reexamination of the herpetofauna of Oaxaca, Mexico: composition update, physiographic distribution, and conservation commentary. Zootaxa, 4996, 201–252. [link]

Parra-Olea, G., García París, M., Hanken, J., and Wake, D.B. (2005). Two new species of Pseudoeurycea (Caudata: Plethodontidae) from the mountains of northern Oaxaca. Copeia, 2005(3), 461–469. [link]

Quintero, E., Thessen, A.E., Arias-Caballero, P., and Ayala-Orozco, B. (2014) A statistical assessment of population trends for data deficient Mexican amphibians. PeerJ, 2, e703. [link]

Rovito, S.M., Parra-Olea, G., Recuero, E., and Wake, D.B. (2015). Diversification and biogeographic history of Neotropical plethodontid salamanders. Zoological Journal of the Linnean Society, 175(1), 167–188. [link]

Wilson, L.D., Johnson, J.D., and Mata-Silva, V. (2013). A conservation reassessment of the amphibians of Mexico based on the EVS measure. Amphibian and Reptile Conservation, 7(1), 97–127(e69). [link]

Species Account Citation: AmphibiaWeb 2024 Pseudoeurycea obesa: Ridge Tail Salamander <https://amphibiaweb.org/species/6530> University of California, Berkeley, CA, USA. Accessed Feb 7, 2025.

Citation: AmphibiaWeb. 2025. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 7 Feb 2025.

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