Chersodromus australis

description

Description of the holotype. Adult female; head length 7.3 mm; snout-vent length 180 mm; tail 40 mm; the tail comprises 22 % of total length; head slightly distinct from neck; snout long, 2.6 times head length, rounded in dorsal aspect, projecting anteriorly beyond lower jaw; rostral 0.6 times broader than high, 1.9 times longer than internasal suture, with posterior end approximately at level of anterior margin of nares; internasals broader than long (length vs width on L / R sides 0.59 / 0.56), rounded anteriorly, in contact laterally with anterior and posterior nasals; prefrontals fused together, posterior corner contacting eye; postnasal plus loreal 0.8 times length of snout, suture between them 0.2 times frontal length; frontal longer than wide (width / length 1.1); supraocular large, in broad contact with prefrontal and parietal, contacting postocular and frontal 1.0 times as long as horizontal diameter of eye; supraocular 1.0 times as long as loreal, forming about posterior half of dorsal margin of orbit, ventral margin not projecting anteriorly beyond margin of orbit, posteriorly exceeding 0.4 times length of posterior margin of orbit; parietals 1.4 times longer than broad,

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species

diagnosis

Diagnosis. Chersodromus australis can be distinguished from all Mexican species of snakes by having combination of prefrontals fused into single scale; postocular discrete from supraocular; single anterior temporal present; dorsal scales keeled in 17 rows at midbody, unreduced posteriorly; supralabials usually 6, third and fourth entering orbit; infralabials 7 – 8, usually 1 – 4 contacting anterior chinshields); mental contacting anterior chinshields; ventral surface of body cream colored. Chersodromus australis differs of C. rubriventris by having 17 scales around body (vs. 15), by having eight infralabials (vs. six or seven), by having a cream colored belly (vs. orange), and by having the mental in contact with first pair of chinshields (vs. not in contact). Chersodromus australis differs from C. liebmanni by having six supralabials (vs. seven), and from the new species that follows by having a dark belly (vs. cream-colored) and in having four infralabials contacting anterior chinshields (vs. five or six) (Table 1).

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species

distribution

Distribution and habitat. Chersodromus australis apparently has a relatively small distribution east of the Isthmus of Tehuantepec (Fig. 1) in the region known locally as Chimalapas; it occurs at low elevations (350 m asl) in tropical rain forest (Fig 7 B). A single specimen was obtained on June 1995 under a rock at 16: 00 hrs on a mountain near San Isidro la Gringa, municipality of Santa María Chimalapa. Other amphibians and reptiles recorded at the type locality included Incilius macrocristatus (Firchein & Smith 1957), Norops pygmaeus (Álvarez del Toro & Smith 1956), Lepidophyma tuxtlae Werler & Shannon 1957, Bothrops asper (Garman 1884), and Tantillita lintoni (Smith 1940).

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species

etymology

Etymology. The specific name is derived from the Latin australis, meaning southern, alluding to the southernmost distribution of species for the genus.

Taxonomic review of the rare Mexican snake genus Chersodromus (Serpentes: Dipsadidae), with the description of two new species