Dog-faced Water Snake

description

Variation. Largest male 777 mm TL with a 135 mm tail; largest female 886 mm TL with a 124 mm tail. Head is elongated, distinct from the neck and depressed; eyes are dorsal and slightly protruding. Many of the smaller head scales anterior to the angle of the jaw have keels. Rostral as tall as broad and pentagonal; nasal may be divided, undivided or semi divided; the nasal cleft may touch labial, internasal, or loreal; internasal divided (rarely single or semi-divided); and usually in broad contact with loreal posterior to the nasals. Frontal fragmented with one or two large anterior fragments and smaller posterior fragments; in most specimens largest remaining fragment shorter than supraocular; parietals fragmented into numerous small scales. Loreal may be single or double, contacts upper labials 1 – 3 or 1 – 4 (rarely 2 – 3 or 2 – 4). Supraocular single (rarely double); preocular single or double, usually one; subocular scales 1 – 3 (usually two), but may be completely absent with 5 th or 6 th upper labial entering the orbit. Upper labials 8 – 10, usually 9, largest upper labial usually 6 (88 % of 96 sides); the last two upper labials horizontally divided. Primary temporal scales m

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

diagnosis

Diagnosis. Cerberus rynchops can be distinguished from all other members of the genus by its 25 (rarely 23) scale rows at midbody, the imbricate plate-like scales on the crown have a flat, thin appearance and are keeled anterior to angle of jaw; the last two upper labial are horizontally divided; the venter is mottled. Cerberus australis has 23 scale rows at mid-body, and the first upper labial does not contact the loreal (it usually does so in all other Cerberus species). Cerberus dunsoni has 23 scale rows at mid body, rounded juxtaposed scales on the crown, and a uniform black venter. Cerberus schneiderii usually has 23 scale rows at mid-body (rarely 21 or 25), the last upper labial is horizontally divided (as opposed to two in C. rynchops), and the venter is mottled.

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

distribution

Distribution. Cerberus rynchops ranges from the vicinity of Mumbai, India along the Indian coast to coastal Bangladesh and Myanmar southward to a point north of Phuket, Thailand. It also occurs in the Andaman and Nicobar Islands. Exactly where its distribution stops and C. rynchops distribution starts is unknown, and we have not found a locality where both species co-exist. An old record from the Sind coast may be an error (see Murphy 2007).

The dog-faced water snakes, a revision of the genus Cerberus Cuvier, (Squamata, Serpentes, Homalopsidae), with the description of a new species

Cerberus rynchops (Schneider 1799)

Cerberus cf. rynchops (Schneider, 1799) Fig. 25 Common names. (E) Bockadam, Dog-faced Watersnake. *(T) Samea natar (samea = snake, natar = rice paddy). Identification. Dog-faced watersnakes are easily distinguished based on both morphology and habits. Compared with other snakes, the head is blunt with a rounded snout and relatively small eyes in a dorsolateral position (Fig. 25). Coloration is brownish gray, often with darker blotches on the back. Relative to most snakes in Timor-Leste, these snakes are heavy-bodied (body diameter is robust as opposed to slender). These snakes are most frequently encountered in habitats with standing or slow-flowing water. Collection and natural history. We captured a single specimen of a snake very similar to Cerberus rynchops at night from a flooded rice paddy near Baucau (Baucau District). The snake submerged when illuminated, but was extracted from the muddy water with ease. Taxonomic comment. In its overall morphology our specimen clearly resembles Cerberus rynchops, but a few specific characteristics of its scalation are intermediate between Cerberus rynchops and Cerberus australis. Until we are able to ascertain its precise

The herpetofauna of Timor-Leste: a first report