Tropidonotus nicobarensis (Sclater, 1891)

Lee, Justin L., Chandramouli, S. R. & Bauer, Aaron M., 2023, Tropidonotus nicobarensis Sclater, 1891 is a junior synonym of Thamnophis saurita (Linnaeus, 1766) (Squamata: Serpentes: Natricinae), Zootaxa 5285 (1), pp. 133-148 : 135-137

Redescription of Tropidonotus nicobarensis

The holotype (ZSI 8895) of Tropidonotus nicobarensis is an unsexed juvenile specimen in fair condition, with an incomplete tail and partially damaged upper jaws ( Figure 1 ). The right maxilla had earlier been dissected out, the incision leaving a blemish in the skin around the temporal region. SVL 164 mm, TailL 61 mm (225 mm TotalL), HeadL 11.0 mm, HeadW 5.0 mm, SnoutL 2.6 mm, EyeD 2.4 mm; TailL/TotalL 0.407, HeadL/ W 2.20, EyeD/HeadL 0.43, EyeD/SnoutL 0.92. Head large and distinct from the neck, ovoid, longer than wide, wider than head depth; eyes large with round pupils, slightly smaller than half the length of the head and shorter than snout; nostrils round and oriented laterally. Rostral barely visible from above; internasals paired and wider than long, small and subtriangular, narrower anteriorly; prefrontals paired and wider than long, pentagonal, suture dividing the two scales less than half the length of the frontal; muzzle length/frontal length ratio 0.510; frontal large, longer than wide, hexagonal and shield-shaped; anterior and posterior sutures of frontal all angled, border with supraoculars convex; parietals paired, longer than wide and subhexagonal; length of each parietal twice as long as frontal. Loreal scale 1/1 and moderately sized, slightly longer than wide and subtrapezoidal; preoculars 1/1, vertically elongate; postoculars 3/3, lowest postocular smallest; supralabials 8/7, with the 4 th and 5 th scales in contact with the orbit on the left side, and the 3 rd and 4 th scales in contact on the right side; 5 th or 6 th supralabial largest and trapezoidal-shaped; temporal scale formula 1+2/1+2 on either side, with the anterior scale broad and subrectangular; infralabials 10/10, with first 1–5 scales in contact with the anterior chin shields and the 4 th scale being the largest. Dorsal scales strongly keeled, in 19–19–17 rows, ventrals 160 (vs. 162 fide Sclater, 1891a), extending onto flanks; cloacal plate undivided; subcaudals paired, 88 under the incomplete tail (vs. 119 fide Sclater, 1891a; 120 fide Smith 1943).

After more than 130 years of preservation, the dorsum is brown overall with a distinct light brown vertebral stripe around 1.0–1.5 dorsal scales wide edged with dark brown, extending from the posterior suture of the parietals to the tail tip; on each flank a small light lateral stripe around 0.5 dorsal scales wide present on the 3 rd to 4 th scale row, starting at the nape near the border of the last supralabial and ending at the start of the tail. The coloration of the head is similar to the dorsum, but the preocular has a small tannish spot bordered by dark brown; supralabial region slightly lighter than temporal region and adjacent upper portions of head. Ventral surface creamy-brown, immaculate, much lighter than dorsum and slightly lighter than dorsal stripes.

According to past authors, the dorsal and ventral coloration of the specimen was much more vibrant. Sclater (1891a) described the dorsum as “bluish olive” and the snout and lateral portions of the head “yellowish” with a “dark streak” behind the eye. Smith (1943) noted the dorsum was Greenish olive above, with 3 light, black edged stripes, but erroneously reported the lateral stripes on the second and third dorsal scale rows, whereas our examination confirms their presence on the third and fourth rows. Smith (1943) also denoted the presence of small black spots edged along the lateral stripes, and the presence of two white spots on either side of the parietal suture. Neither characteristic is visible in current photographs of the holotype. Discrepancies in the number of ventral scales are probably indicative of different counting procedures, as Dowling (1951) ’s method was not used during the 19 th and mid 20 th century. Furthermore, the number of subcaudals is lower than past reports, but because the tail appears to be broken, it is possible this could be the result of damage since the specimen was last examined. Contrasting the conditions reported by Sclater (1891a) and agreeing with subsequent revisers, we confirm that the cloacal plate is undivided. The right maxilla was probably dissected out by Annandale (1905) because in-text he mentioned that he removed the bone to examine the dentition. Annandale (1905) reported a maxillary tooth count of 24, whereas Wall (1923) counted 25 teeth. Both authors noted that the teeth are gradually enlarged posteriorly.

Figures

FIGURE 1. Historical images of (a) William Lutley Sclater (1863–1944), the author of the description of Tropidonotus nicobarensis; (b) Frederik Adolph de Röepstorff (1842–1883), alleged collector of its type specimen; and (c–f), the original lithographic illustrations of Tropidonotus nicobarensis (Sclater 1891a, pl. 6, figs 5). Images of (a) from Grant (1945), (b) from illustration published in newspaper The Graphic, 17 May 1884, author unknown, and (c–f) illustrated by S. C. Mondul in Sclater (1891a: pl. 6).