The imagery on this page is the basis for a paper entitled Taxonomic status of the enigmatic salamander Cryptotriton adelos (Amphibia: Plethodontidae) from northern Oaxaca, Mexico, with observations on its skull and postcranial skeleton by D.B. Wake, S.M. Rovito, J.A. Maisano and J. Hanken (2012, Zootaxa, 3579, 67-70). The Introduction is as follows:

Papenfuss and Wake (1987) described a new species of plethodontid salamander from northern Oaxaca, Mexico, which they named Nototriton adelos. The species was assigned to Nototriton primarily on the basis of its similarity to members of that widespread genus, which as then constituted ranged from Oaxaca, Mexico, to east-central Costa Rica. At that time, Nototriton had no unique synapomorphies but rather included diminutive species that could be excluded from membership in all other genera. Wake and Elias (1983), who erected Nototriton, acknowledged that the genus might eventually be shown to be paraphyletic, but they were unable to further resolve the phylogeny with information then available. The original description of N. adelos was based on the holotype and three paratypes; in the subsequent 25 years, despite many futile attempts, only one additional specimen of this species has been discovered: UTAVC A-3956, the largest known specimen, a female, 25.6 mm snout-vent length, from near the type locality.

From the start, assignment of the species to Nototriton was problematic on zoogeographic grounds: it was the only member of its genus from north of the Isthmus of Tehuantepec in southeastern Mexico. Later, when DNA sequence data demonstrated conclusively the paraphyly of Nototriton, N. adelos was transferred to the newly erected genus Cryptotriton (García-París & Wake 2000), but in the absence of sequence data for this species. Once again, however, C. adelos was the only member of its genus from north of the Isthmus of Tehuantepec.

Hanken’s (1983) study of allozymic variation in the endemic Mexican plethodontid genus Thorius included a single specimen of Cryptotriton adelos, but Papenfuss and Wake (1987) subsequently argued that this specimen, and the species to which it belongs, was not a member of Thorius. Cryptotriton adelos lacks the unique subocular groove (orbitolabial groove; Taylor 1944), which intercepts the upper lip and gives a characteristic and distinctive lateral profile to the head in all known species of Thorius (Taylor 1940, Plate XLVII; Gehlbach 1959, Fig. 1).

All efforts to collect more specimens of C. adelos have been fruitless, thereby precluding additional molecular analyses that might help resolve the species’ generic assignment. We therefore decided to examine the osteology of the species by using high-resolution X-ray computed tomography (CT) in an attempt to discover skeletal features that might be phylogenetically informative. Digital scans of a single adult specimen (MVZ 208582, a male, 23.8 mm snout-vent length; www.digimorph.org/specimens/Thorius_adelos) reveal a combination of characters, which while unusual for Thorius in some respects includes features that otherwise are unique to that genus. Furthermore, the osteology of C. adelos excludes it from membership in any other clade of tropical plethodontids. Accordingly, we reassign the species as follows:

Thorius adelos (Papenfuss & Wake 1987)
Nototriton adelos Papenfuss & Wake 1987, p. 7
Cryptotriton adelos (Papenfuss & Wake 1987), García-París & Wake 2000, p. 58

This adult male specimen, a paratype, was collected from La Hesperanza, Tuxtepec, Oaxaca Mexico on 8 August 1973. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. David Wake of the University of California Museum of Zoology and Dr. James Hanken of Harvard University. Funding was provided by Dr. Hanken.

This specimen was scanned by Jessie Maisano on 3 June 2011 along the coronal axis for a total of 2402 slices with a resolution of 4.53 microns.

Literature

AmphibiaWeb (2012) Information on amphibian biology and conservation. Berkeley, California. Available from: http://amphibiaweb.org/ (accessed October 23, 2012).

García-París, M. & 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.

Gehlbach, F.R. (1959) New plethodontid salamanders of the genus Thorius from Puebla, Mexico. Copeia, 1959, 203–206.

Hanken, J. (1982) Appendicular skeletal morphology in minute salamanders, genus Thorius (Amphibia: Plethodontidae): growth regulation, adult size determination, and natural variation. Journal of Morphology, 174, 57–77.

Hanken, J. (1983) Genetic variation in a dwarfed lineage, the Mexican salamander genus Thorius (Amphibia: Plethodontidae): taxonomic, ecologic, and evolutionary implications. Copeia, 1983, 1051–1073.

Hanken, J. (1984) Miniaturization and its effects on cranial morphology in plethodontid salamanders, genus Thorius (Amphibia: Plethodontidae). I. Osteological variation. Biological Journal of the Linnean Society, 23, 55–75.

Hanken, J. & Wake, D.B. (1994) Five new species of minute salamanders, genus Thorius (Caudata: Plethodontidae), from northern Oaxaca, México. Copeia, 1994, 573–590.

Hanken, J. & Wake, D.B. (2001) A seventh species of minute salamander (Thorius: Plethodontidae) from the Sierra de Juárez, Oaxaca, Mexico. Herpetologica, 57, 515–523.

Papenfuss, T.J. & Wake, D.B. (1987) Two new species of plethodontid salamanders (genus Nototriton) from Mexico. Acta Zoologica Mexicana (ns), 21, 1–16.

Taylor, E.H. (1940 “1939”) New salamanders from Mexico with a discussion of certain known forms. The University of Kansas Science Bulletin, 26, 407–439.

Taylor, E.H. (1944) The genera of plethodont salamanders in Mexico, Pt. I. The University of Kansas Science Bulletin, 30, 189–232.

Wake, D.B. (1966) Comparative osteology and evolution of the lungless salamanders, family Plethodontidae. Memoirs of the Southern California Academy of Sciences, 4, 1–111.

Wake, D.B. (1970) Aspects of vertebral evolution in the modern Amphibia. Forma et Functio, 3, 33–60.

Wake, D.B. (1991) Homoplasy: the result of natural selection, or evidence of design limitations? American Naturalist, 138, 543–567.

Wake, D.B. & Elias, P. (1983) New genera and a new species of Central American salamanders, with a review of the tropical genera (Amphibia, Caudata, Plethodontidae). Contributions in Science, Natural History Museum of Los Angeles County, 345, 1–19.

Wake. D.B., Papenfuss, T.J. & Lynch, J.F. (1992) Distribution of salamanders along elevational transects in Mexico and Guatemala. In: Darwin, S.P. & Weldon, A.L. (Eds.), Biogeography of Mesoamerica: Proceedings of a Symposium. Tulane Studies in Zoology and Botany, Suppl. Publ. no. 1, New Orleans, pp. 303–319.

None available.