Hanken's Minute Salamander
Species Description: Campbell JA, Brodie Jr ED, Flores-Villela O, Smith EN 2014 A fourth species of minute salamander (Thorius; Plethoodntidae) from the Sierra Madre del Sur of Guerrero, Mexico. So Amer J Herp 9: 46-51.
It differs from other Thorius species by the following combination of characteristics: relatively short head; fairly large nostrils; relatively short limbs and tail; webbing on the toes reaching three quarters of length; rounded fingertips and toetips that are the same length to the pad; small glands on back with small openings; relatively few vomerine teeth; no maxillary teeth; very few premaxillary teeth; a wide dark reddish-brown stripe that runs from head to end of tail; and black flanks spotted with many white markings. Thorius grandis differs from T. hankeni by the former having the following characteristics: toes webbed to only half the length; more premaxillary teeth; maxillary teeth present in females. Thorius omiltemi differs from it through the following characteristics: elongated nostrils (vs. ovate); toes webbed to only half the length; more vomerine teeth; huge glands on back (vs. small glands). Thorius infernalis differs from it through the following characteristics: smaller body size; small and elliptical nostrils; pointed fingers and toes (Campbell et al. 2014).
In life, it has a wide dark reddish-brown stripe that runs from the head to the end of the tail. The mid-back has a faint dark brown line composed of shorter uneven dark lines. The region between the snout and the eyelids is similar in color to the back, whereas the rest of the head is a darker brown. There are prominently dark grooves on the head. The regions of the hands, feet, and limbs furthest away from the body are black with white dots. The sides of the head, body, and tail are black with white flecks. The underside is black with white flecks. The iris is dark brown to black. In alcohol, the head is dark brown with mildly darker Y-shaped patterns. There is a wide brown band running from the neck to the tail. The underside of the head down to the cloaca is black with white flecks. The underside of the tail is light brown and lacks flecks. The backsides of the forearm and lower leg are black with some white flecks (Campbell et al. 2014).
There is slight variation in coloration variation. In one paratype, the band on the back is mildly darker, a darker zigzag pattern is present on the back, and white flecking is present lower on the sides. In two paratypes, there is also a zigzag pattern, and the sides are black with a few white flecks (Campbell et al. 2014).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
Trends and Threats
Due to the unusual morphological characteristics of Thorius as well as the lack of obvious external variation within the genus, the phylogenetic placement of Thorius has been controversial since its discovery, as are the taxonomic relationships within the genus. It is currently recognized as one of twelve genera within the Bolitoglossini, a tribe of plethodontid salamanders. It has been suggested that the high level of species diversity within Thorius (currently 25 species) is a result of not only allopatric speciation through processes such as range fragmentation, but also of adaptive radiation. Several sympatric species of Thorius differ by traits such as body size and presence/absence of maxillary teeth, traits that may allow these sympatric species to partition available niche space. Such adaptive morphological divergence would allow for high species richness to evolve in a small range (as is the case for Thorius) and would account for the significant level of morphological differentiation between sympatric species observed in Thorius as well (Rovito et al. 2013, Wake 2012).
The species is named after Dr. James Hanken, a prominent researcher of the genus Thorius (Campbell et al. 2014).
The Thorius genus exhibits extreme miniaturization, and is characterized by tiny body size, skeletal reduction, and unique skeletal features. This genus contains the smallest terrestrial tailed vertebrates, with adults of some species having a snout-vent length of less than 20 mm (Hanken 1986, Rovito et al. 2013).
Campbell, J. A., Brodie, Jr., E. D., Flores-Villela, O., Smith, E. N. (2014). ''A Fourth Species of Minute Salamander (Thorius: Plethodontidae) from the Sierra Madre del Sur of Guerrero, Mexico.'' South American Journal of Herpetology, 9(1), 46-51.
Hanken, J. (1986). ''For Some Species, Reduced Size Is the Key to Survival.'' The Sciences, 26(5), 40-43.
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. (2012). ''Taxonomy of Salamanders of the Family Plethodontidae (Amphibia: Caudata).'' Zootaxa, 3484, 75-82.
Written by Sofia Prado-Irwin (spradoirwin AT gmail.com), San Francisco State University
First submitted 2015-09-16
Edited by Gordon Lau (2015-09-21)
Species Account Citation: AmphibiaWeb 2015 Thorius hankeni: Hanken's Minute Salamander <http://amphibiaweb.org/species/8156> University of California, Berkeley, CA, USA. Accessed Sep 22, 2018.
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Citation: AmphibiaWeb. 2018. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Sep 2018.
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