Friday, April 8, 2016

Double-lined Water Snake, Thamnodynastes ramonriveroi (Family Dipsadidae)

Thamnodynastes ramonriveroi Manzanilla & Sánchez 2005

Thamnodynastes ramonriveroi — Bailey & Thomas 2007





Size: 600 mm TL. Identification: The only Trinidad snake with 19 rows of smooth scales, light and dark dorsolateral stripes and a venter flecked with brown pigment. Rostral barely visible from above; nasals entire; one preocular; two postoculars; two primary temporals; eight upper labials, with the fourth and fifth entering orbit; eight lower labials with the first four contacting the anterior chin shields; smooth dorsal scales in 19 rows at mid-body, reduce to 17 posteriorly; ventrals 137–153; cloacal plate divided; paired subcaudals 59–75. Distribution: Coastal Suriname through eastern Venezuela (both uplands and the Orinoco Delta) and southwest Trinidad. Habitat: Semi-aquatic, in secondary forest and agricultural areas in southwest Trinidad. Biology: Nocturnal. Diet includes fish and tadpoles.

The following is adapted from Bailey and Thomas (2006)

Thamnodynastes ramonriveroi ranges from near sea level to at least 1750 m on Mt. Turumiquire on the Sucre-Monagas-Anzoategui border in Venezuela. The upland and coastal populations differ somewhat. The only Brazilian specimen, from the alto Rio Catrimany (MNRJ 668), Rio Branco, was long believed to be the only apparent specimen of Thamnodynastes strigatusfrom the north, some 3000 km from the nearest conspecific; but there was no other reason to question its provenance. In fact, Franco and Ferreira (2003) recently cited this specimen and another as evidence for a northern population of T. strigatus. With the discovery of T. ramonriveroi as a valid species, the identity of MNRJ 668 is solved, as it compares perfectly with the type series; however, it’s locality lies 930 km south of Mt. Turumiquire and 650 km from the closest Guiana records. Boos (1984) reported the first known specimen from Trinidad (there are now three existing from that island – see Murphy 1997, Boos 2001); he called it Thamnodynastes strigatus. The only congener sympatric with Thamnodynastes ramonriveroi is T. pallidus, both of which are recorded from Nieuw Nickerie and Paramaribo, Suriname, and from Demerara (Georgetown), Guayana. All localities are in areas of original forest. The species is semi-aquatic. An Elvécia specimen was noted by Netting: “Caught crawling in a small pool. Swam easily and well. Flattened the entire first half of body and when tormented opened mouth very widely; played possum when struck with a light stick” (the flattening behavior is shown in Manzanilla and Sánchez 2005. His field notes for another specimen give the local name as ”mapanare del agua”. A preserved specimen from Guyana had a small cyprinodontid fish in its mouth, and one from Suriname had eaten a metamorphosing tadpole. Three gravid females have been examined: CM 7977, 337 mm SVL, with five embryos, was taken January 13, 1930; RMNH 990, 365mm SVL, contained four embryos; and in AMNH 36119, 348mm SVL, two eggs were observe.

Diagnosis. A northern dwarfed relative of Thamnodynastes strigatus, from which it differs chiefly in its smaller size, lesser development of para-cloacal tubercles in males, a higher modal maxillary tooth count, and in possessing enlarged basal hooks on the hemipenis. Description of a typical specimen. An adult male (CM 7981), collected by M.G. Netting on January 14, 1930, at Elvécia, Sucre State, Venezuela.

A medium-sized, rather stocky snake with smooth dorsal scales in the formula 19- 19-15, reducing twice by the loss of the fourth lateral row opposite ventrals 69 and 84, respectively; a single scale pit is distinct on most of the scales that have not slipped; ventrals 147; cloacal plate divided; subcaudals 62 plus a terminal spine; supralabials 8- 8, third (very narrowly) to fifth entering the orbit; infralabials 9-9, the anterior five in contact with the genials; one pre and two postoculars on each side; nasal divided below nostril; loreal with its lower margin nearly twice as long as the upper; two temporals contact the postoculars; paracloacal tubercles scarcely evident; TL 492mm; tail 112mm; tail/SVL ratio 22.8%; HL 18.5mm; orbit 3.3mm, projecting to front of nostril; maxillary teeth 16+2G. Nuchal pale stripe about 13 scales long before being interrupted into a series of mid-dorsal pale spots about the size of the eye; ground color slate gray where scales have slipped and brown where they are present; scales between and on either side of pale dorsal spots are edged with black on the anterior part of the body becoming inconspicuous posteriorly; a dark lateral stripe follows the fourth lateral row; the top of the head is gray with darker mottling; the eye to angle of jaw stripe is well developed, meeting the orbit on the postocular suture and continuing anteriorly from orbit to nostril; five pale centered dark spots on the supralabials, the largest on the fifth, plus a few irregular smaller markings; chin bars and scattered dark spots present on the throat; five rows of dark spots with paler centers on the ventrals with additional pigment between the rows, the outermost pair of which are much the darkest and separated from the dorsal color by a narrow pale line, which is not sharply demarcated. CM 7981 is described in Netting’s field notes as follows: “greenish above with dark blackish spots and light greenish between markings below, iris light brown.”

Bailey J.R, R.A Thomas 2007. A revision of the South American snake genus Thamnodynastes Wagler, 1830 (Serpentes, Colubridae, Tachymenini). II. Three new species from northern South America, with further descriptions of Thamnodynastes gambotensis Pérez-Santos and Moreno and Tha Memoria de la Fundación La Salle de Ciencias Naturales 166: 7-27 [2006]

Cole, CJ,CR Townsend, RP. Reynolds, RD MacCulloch, & A Lathrop 2013. Amphibians and reptiles of Guyana, South America: illustrated keys, annotated species accounts, and a biogeographic synopsis. Proceedings of the Biological Society of Washington 125 (4): 317-578; plates: 580-620

Manzanilla, J. & Sánchez 2005. Una nueva especie de Thamnodynastes (Serpentes: Colubridae) del macizo del Turimiquire, noreste de Venezuela. Memorias de la Fundación La Salle de Ciencias Naturales 161-162: 61-75 [2004]

Natera-Mumaw, M; LF Esqueda-González & M Castelaín-Fernández 2015. Atlas Serpientes de Venezuela Santiago de Chile, Dimacofi Negocios Avanzados S.A., 456 pp.

Rivas, GA.; CR Molina, G N Ugueto, TR. Barros, CL. Barrio-Amorós & PJK Kok 2012. Reptiles of Venezuela: an updated and commented checklist. Zootaxa 3211: 1–64

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