Abstract
A new species of the Rhadinaeadecorata group is described based on two specimens from the Sierra Madre del Sur, Guerrero, Mexico. The new species differs from all other members of the genus Rhadinaea by having: eight supralabials; 149–151 (male) ventrals; 63–77 (male) subcaudals; two large pale nuchal blotches, forming an incomplete collar that occupies two scales laterally and is bissected along the dorsal midline; a postocular pale marking consisting of a well-defined, narrow line beginning behind the upper posterior margin of the eye and extending posteriorly nearly horizontally until connecting with the nuchal blotches; and the dark ground color of the flanks extending to the lateral portion of the ventrals. The large nuchal blotches distinguish the new species from the other members of the R.decorata group, except for R.cuneata and some individuals of R.hesperia (pale nuchal marking one-scale wide in R.marcellae, absent in the other species). The condition of the postocular pale marking distinguishes it from R.cuneata and R.hesperia (postocular pale marking wedge-shaped in R.cuneata, not connected with the pale post-cephalic markings in R.hesperia). Furthermore, the number of subcaudals and the coloration of the lateral portion of the ventrals distinguish it from R.omiltemana and R.taeniata, the remaining congeners found in Guerrero (85–90 in males of R.omiltemana and 91–121 in R.taeniata; dark color of the flanks not reaching ventrals in the former species, occasionally and faintly in R.taeniata). Additionally, a new combination for R.stadelmani is proposed. The new species is the first described in the genus Rhadinaea in more than 40 years.
Highlights
Snakes of the genus Rhadinaea Cope, 1863 (Colubridae: Dipsadinae) are distributed throughout Mesoamerica, ranging from the Sierra Madre Occidental of southern Sinaloa and Sierra Madre Oriental of northern Nuevo León in Mexico to northwestern Ecuador in South America, with an isolated species, R. flavilata (Cope, 1871), in the southeastern USA (Myers 1974)
We examined the hemipenial morphology in the new species after removal of the right hemipenis from the preserved holotype
Morphological examination of the specimens from El Molote supported their inclusion in the genus Rhadinaea, based on the following combination of traits (Myers 1974): hemipenis symmetrical, distally calyculate, unicapitate, spinose; sulcus spermaticus bifurcate; pupil round; full complement of colubrid head plates; subpreocular present; dorsal scales smooth, arranged in 17 rows with no posterior reduction; head with distinctive markings; body brown with longitudinal dark lines
Summary
Snakes of the genus Rhadinaea Cope, 1863 (Colubridae: Dipsadinae) are distributed throughout Mesoamerica, ranging from the Sierra Madre Occidental of southern Sinaloa and Sierra Madre Oriental of northern Nuevo León in Mexico to northwestern Ecuador in South America, with an isolated species, R. flavilata (Cope, 1871), in the southeastern USA (Myers 1974). According to Myers (2011), the genus contains 20 species arranged in six species groups, mainly on the basis of their external morphology. These groups are (number of species in each group in parentheses) the R. calligaster (1), R. decorata (11), R. flavilata (2), R. taeniata (3), and R. vermiculaticeps (3) groups. No new species of Rhadinaea (sensu Myers 2011) has been described since Myers’ systematic monograph of the group in 1974. The body is either striped or lined, with at least a hint of a narrow, linear dark marking involving dorsal scale rows 4 or 5, occasionally bordered above by a pale streak or series of small pale spots. The tail comprises between 25% and 48% of the total length
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