Atractus microrhynchus ( Cope, 1868 )

Passos, Paulo, Mueses-Cisneros, Jonh Jairo, Lynch, John D. & Fernandes, Ronaldo, 2009, Pacific lowland snakes of the genus Atractus (Serpentes: Dipsadidae), with description of three new species, Zootaxa 2293, pp. 1-34 : 19-20

Atractus microrhynchus ( Cope, 1868)

Rhabdosoma microrhynchum Cope, 1868 ; Proc. Acad. Nat. Sci. Philadelphia 1868:102.

Atractus badius— Boulenger, 1896; Catalogue of the Snakes in the British Museum vol. 2:308. (part.). Atractus microrhynchus – Savage, 1960; Misc. Publ. Mus. Zool. Univ. Michigan 112:2.

Atractus badius— Dixon and Soini, 1977; Contrib. Biol. Geol. Milwaukee Publ. Mus. 12:33. Atractus microrhynchus— Dixon and Soini, 1986; Milwaukee Public Museum 12:52.

Holotype: Unknown sex, California Academy of Science ( CAS 6693), from Guayaquil (02º10’S, 79º54’W, ca. 50 m), province of Guayas, Ecuador, collected by the Orton Expedition in 1865. Savage (1960) pointed out that the holotype was missing at the CAS and it is probably lost (see Remarks).

Diagnosis: Atractus microrhynchus is distinguished from all congeners by the following combination of characters: (1) 17/17/17 smooth dorsals; (2) one or two postoculars; (3) loreal long; (4) temporals 1+2; (5) seven supralabials, third and fourth contacting orbit; (6) unknown number of infralabials, first two contacting chinshields; (12) dorsum uniformly dark brown, with a incomplete occipital light band; (13) venter light brown with dark brown dots in the lateral region of ventrals; (14) small body size (but the age and sex were unreported in the original description, likely based on a juvenile specimen), holotype about 100 mm SVL.

Comparisons: The brief data available from original description are inadequate to distinguish it from many Atractus having 17 scale rows and uniform colour pattern. Still, the lacking of illustration on description precludes the confirmation of some uncommon Atractus features (only two pairs of infralabials contacting chinshields) of A. microrhynchus . Nonetheless, if the original description is accurate, A. microrhynchus shares only with A. alphonsehogei , A. caxiuana , A. collaris , A. gaigeae , A. limitaneus , and A. surucucu : 17 dorsal scale rows; seven infralabials, with third and fourth contacting orbit; dorsum uniformly dark brown colour; incomplete occipital light band; and lateral portion of ventral scales dark brown pigmented. Atractus microrhynchus differs from these six species in having a light brown venter and only two pairs of infralabials contacting chinshields (vs. venter uniformly creamish white and three pair of infralabials contacting chinshields).

Description (according Cope 1868): Rostral broader than high; nasal divided; prenasal higher; internasal of similar size to postnasal; postnasal 1/6 of the parietal size; frontal sub-triangular; parietal longer than wide; loreal long; sixth supralabial longer than high; one or two postoculars; temporal 1+2; upper posterior temporals elongate; seven supralabials, third and fourth contacting orbit; first pair of infralabials in contact behind symphisial, preventing symphisial/chinshields contact; first two infralabials contacting chinshields; 17/17/17 smooth dorsal scale rows.

Colour in preservative (according to Cope 1868): Dorsum of head with black cap, extending from frontal to neck; black cap interrupted by incomplete creamish yellow occipital band; occipital band extends from parietals to rictus of mouth; background of head dark brown to median portion of supralabials; supralabials with light brown ventral margin; venter light brown with lateral portion of ventrals dark brown pigmented; dorsum uniformly dark brown.

Distribution: Known only from Guayaquil in the province of Guayas, Ecuador. Atractus microrhynchus apparently inhabits Lowland Seasonal Evergreen forest near sea level ( Fig. 6 ).

Remarks: Cope (1868) described Rhabdosoma microrhynchum based on a single individual, suggesting it was close related to Atractus badius . Cope (1871) reported R. microrhynchum from Pebas (= Pevas) in the Amazon lowlands of Peru on the basis of new material also from the Orton Expedition. Boulenger (1896) redefined the genus Atractus and synonymized R. microrhynchum with A. badius , without providing any comments. Savage (1960) resurrected A. microrhynchus , but considered that because Cope’s description was so brief, the taxonomic status of this species could not be accurately addressed. Dixon and Soini (1977) proposed the synonymy of A. microrhynchus with A. badius based on specimens from the Iquitos region in Peru, stating that the type locality was erroneous and the species was probably Amazonian. Hoogmoed (1980) redescribed the lectotype of A. badius and did not consider A. microrhynchus as a synonym of that species. Dixon and Soini (1986) re-considered their synonymy and refered to the same specimens as Atractus cf. microrhynchus . The Dixon and Soini specimens actually refer to A. natans , recently described by Hoogmoed and Prudente (2002) (Passos 2008).

The type locality of Atractus microrhynchus is Guayaquil in Ecuador, but there are no other reports of Atractus from this locality (Savage 1960; Peters & Orejas-Miranda 1970; Passos 2008). Savage (1960) suggested the possibility that the type locality was in error, given that the Orton Expedition collected material also in the Amazonian lowlands. Given the possibility of an incorrect type locality, brief available description, and loss of the holotype of A. microrhynchus , perhaps we should consider it as a nomen dubium (ICNZ 1999). Nevertheless, most snake species from the Orton Expedition labelled from the Pacific lowlands of Ecuador in fact occur there (e.g., Trachyboa gularis , Pelamis bicolor , and Micrurus mipartitus ). Furthermore, recent specimens from the Pacific lowlands of Ecuador collected a few kilometres from the type locality apparently conform well to Cope’s description, suggesting it may be a valid taxon (D. Cisneros-Heredia, pers. comm.). Therefore, we prefer to maintain the status quo of recognizing A. microrhynchus , while waiting the formal report of the aforementioned specimens.

Figures

FIGURE 6. Geographical distribution of the Atractus paucidens species group.