Dendrelaphis nigroserratus, the Sawtooth-necked Bronzeback

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Figure 1: A subadult Sawtooth-necked Bronzeback in Tak’s Umphang district, at an elevation of about 1200 m.

Sawtooth-necked Bronzeback
Dendrelaphis nigroserratus Vogel, Van Rooijen & Hauser, 2012
Proposed Thai name: ngu sai man kho dok lueai si dam – งูสายม่าน คอดอกเลื่อยสีดำ

This beautiful species was first described in 2012. (1)  It is only known from relatively isolated border areas in Phetchaburi, Kanchanaburi and Tak provinces and adjacent areas in southeastern Myanmar, which is one reason for its late discovery.

The striking similarities of its meristic characters with those of the Blue Bronzeback (Dendrelaphis cyaonochloris) made Pauwels and co-authors (2) refute it as a distinct species, despite its different color and its highly distinctive pattern of the neck.
It differs from D. cyanochloris by the conspicuous sawtooth-shaped pattern of the neck and its larger size. A minor difference is the high incidence of two paired central postparietal scales where D. cyanochloris usually has a single central post-parietal scale.

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Figure 2: Details of the neck pattern.

The anterior one third of the body has black oblique bars, superficially resembling Cohn’s bronzeback (Dendrelaphis stiatus). The latter is known from southern Thailand, West-Malaysia, Sumatra and Borneo, is considerably smaller and has fewer ventral scales. What’s more, in D. striatus the neck is bright yellow without any pattern.
The largest specimen of the Sawtooth-necked Bronzeback thusfar recorded was 163 cm (Hauser and Vogel, forth coming), but records of even larger ones are to be expected—it is by far the largest representive of the genus Dendrelaphis in northern Thailand where it is only known in Tak Province’s Phop Phra and Umphang Districts.
The head and back of this snake are greenish bronze, whereas the belly is yellowish or greyish green. Most remarkable is the broad black postocular streak that starts at the eye, continues as a broad bar on the neck where it  breaks up incompletely, resulting in a saw-toothed pattern. Two head lengths behind the head, it breaks up completely in broad oblique bars that fade away at midbody.

No such neck pattern is known from any other bronzeback species. The specific nomen in the scientific name and the English name refer to this serrated pattern of the neck.
The vertebral scales are much enlarged, as they are in the Blue Bronzeback. There is no black or cream lateral stripe. The tongue is bright red.

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Figure 3: The same specimen from figures 1 and 2 crossing a mountain road.

The new species is best known from southern Tak Province in Thailand’s northern region where I came across half a dozen of living specimens and many road kills during the past seven years. It seems to be rather common in hill evergreen forests at elevations of over 800 metres, in particular near streams and in bamboo thickets. Occasionally, it is seen at lower elevations.

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Figure 4: An adult Sawtooth-necked Bronzeback on a tree branch arching a mountain stream in Tak’s Umphang District.

A specimen in the Britisch Museum of Natural History in London had been collected in Mergui in Burma (now Myanmar) in the early 20th century. In Thailand’s Kaeng Krachan National Park in Phetchaburi and Prachap Khiri Khan Province — bordering Myeik (Mergui) District in Myanmar’s Taninthayi Division — a specimen was photographed while swallowing a Wallace’s Flying Frog (Rhacophorus nigropalmatus). The location was initially reported as lowland. (http://www.ecologyasia.com/verts/snakes/sawtooth-necked-bronzeback.htm)
The species has also been reported from western Kanchanaburi Province and pictures were made of a specimen near the Kroeng Krawia Waterfall in the province’s Sangkhlaburi District. (3)
I never came across this snake north of Phop Phra at 16º 35′ N, which is probably the northern limit of this species. However, I expect that it also occurs in mountainous areas east of Phop Phra and Umphang (Kamphaeng Phet’s Khlong Lan District and in the most western mountainous parts of Nakhon Sawan and Uthai Thani Provinces.

dendrelaphis-nigroserratus-05dendrelaphis-nigroserratus-06Holotype

The holotype (QSMI 1282) of the new species is a juvenile from Umphang District, Tak Province, collected in 2011 by Sjon Hauser. It is preserved and stored at the Queen Saovabha Memorial Institute (Bangkok Snake Farm on Rama IV Road) in Bangkok, Thailand.

The holotype is a juvenile female with a total length of 42.8 cm, the tail (13.5 cm) comprising 31.5 % of the total length. It has a very large eye with a horizontal diameter of 0.4 cm.

Figure 5 (left): Details of head and anterior part of the body of a juvenile from Umphang District. Notice the large eye with golden iris. Figure 6 (right): Details of head and neck of a 163 cm long female road kill from Umphang District (SH12.10.13-10).

The smooth dorsal scales are in 17-15-11 rows. The vertebral scales are notably enlarged. It has 201 ventral and 150 paired subcaudal scales. The anal shield is divided.
For the other characters see: Vogel, Van Rooijen and Hauser, 2012. (1)

©SJON HAUSER: text and pictures

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Figure 7: The holotype QSMI 1282 of Dendrelaphis nigroserratus.

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Figure 8: Habitat of Dendrelaphis nigroserratus in Umphang, Tak.

References

(1) Vogel, Gernot, Johan van Rooijen and Sjon Hauser, 2012. A new species of Dendrelaphis Boulenger, 1890 (Squamata: Colubridae) from Thailand and Myanmar. Zootaxa 3392: 35-46.

(2) Pauwels, Olivier S. G., Patrick David, Chucheep Chimsunchart, and Kumthorn Thirakhupt, 2003. Reptiles of Phetchaburi Province, Western Thailand: a list of species, with natural history notes, and  a discussion on the biogeography at the Isthmus of Kra. The Natural History Journal of Chulalongkorn University 3 (1): 23-53.

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Figure 9: Map of Thailand and adjacent areas. Black dots indicate where Dendrelaphis nigroserratus has been recorded.

(3) Seesook, W., 2000. Ngoo-sai-man. Sarakadee Feature Magazine, Bangkok, 179: 110-111 [in Thai, cited in Pauwels et al., 2003].