Sphenomorphus anomalopus, (Boulenger, 1890) (Boulenger, 1890)

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Natural history observations. The specimen was observed on the eastern edge of Gunung Leuser National Park   GoogleMaps at 3°32'58"N, 98°06'37"E ( Fig. 1B View FIGURE 1 – 3 View FIGURE 3 ). The observation site was situated at an elevation of 200 meters above sea level, near the park boundary, approximately 1.5 km upstream from the village of Bukit Lawang, an ecotourism hub. This observation extends the known altitudinal range for the species, which was previously documented up to 60 meters above sea level ( Iskandar et al., 2018). The skink was observed basking along a rainforest trail at 13:18 on 30 November 2024. A gap in the canopy allowed sunlight to reach the ground, providing suitable basking conditions. The   GoogleMaps weather was sunny at the time of the sighting, though the previous evening and night experienced heavy rainfall. The   GoogleMaps skink was approximately 50 m from the Bahorok River   GoogleMaps ( Fig. 2A View FIGURE 2 ) and approximately 100 m from a small stream waterfall ( Fig. 2B View FIGURE 2 ). Marco Mora   GoogleMaps (pers. comm. 2024) noted he observed “several…on the narrow jungle paths” in the vicinity of Bukit Lawang Village   GoogleMaps . The soil in the area is predominantly clay, covered with rainforest leaf litter, interspersed with small rocks, granite boulders, and undergrowth. The   GoogleMaps specimen was on the ground and moved approximately two meters during a three-minute observation period. It exhibited a snake-like tongue-flicking behavior with its pale, forked tongue, which we interpret as a predator evasion behavior in response to observer disturbance. When approached for close-up photography, it moved in short bursts before taking refuge in a cavity beneath a boulder.

Local Knowledge. Discussions with local residents and guides provided some additional anecdotal information regarding the species’ occurrence in the area. Of two wildlife guides consulted, one was unfamiliar with the species, while the other referred to it as a “butterfly lizard.” Among five local villagers shown photographs of the skink, three had no prior knowledge of it. One local guide, who frequently traverses the trail system, reported seeing the species “many times” on sunny days along a trail on the opposite side of the river ( Fig 3A View FIGURE 3 ). Another villager, a gardener living across the river from the observation site, identified a specific area in his backyard where he claimed to have seen the species ( Fig. 3B View FIGURE 3 ). The area is open and highly disturbed with weedy vegetation interspersed amongst the granite rocks. These observations are subjective and provide supplementary context rather than rigorous evidence of the species’ distribution or habitat use, and they may offer insights on potential areas for future targeted surveys.

Color pattern of living specimens. Male coloration and pattern (n=5 on iNaturalist; n=1 herein, Fig. 4B–E View FIGURE 4 ). The ground color of the top of the head is a dull reddish-brown that transitions subtly into dark gray on the dorsum, sacral region, and tail. The sides of the head from the ear opening to the nasal region are reddish-brown and bear a sharp dorsal transition—across a dark canthal stripe—with the darker dorsal surface of the head and rostrum. The upper and lower palbebral scales are whitish and notably outline the eye. Posteriorly , reddish brown on the side of the head transitions smoothly across the neck into dark gray flanks. The flanks are overlain by a series small, irregularly shaped, ventrolateral row of short elongate white markings extending from the neck through the groin and down the length of the tail. Dorsal to these, are series of small, transversely oriented, irregularly shaped dorsolateral white markings that are the lateral, unfaded remnants, of the faded semi-transversely oriented light-colored dorsal bands. The dorsolateral markings coalesce with the faded dorsal bands and continue onto the anterior two-thirds of the tail as a series of regularly spaced, dull-white, broken bands after which the tail is generally uniformly dark grey. The throat and gular region are beige and sharply transition to lemon-yellow at the back of the throat. Lemon-yellow extends across the pectoral region and belly to just anterior to the cloacal region. The yellow coloration extends dorsally up the side of the body to near the level the dorsal margin of the limb insertions on the body. All ventral surfaces are immaculate although faint oblique baring may occur in the Penang population based on our examination of the types. A short transition of lemon-yellow to orange in the cloacal region with orange extending onto the immaculate subcaudal region for at least one-half the length of the tail. Ventrolaterally, the subcaudal orange coloration abruptly contacts the dark grey dorsal coloration of the tail. The dorsal ground color of the limbs hands and feet are greyish much like that of the flanks but with a slight reddish hue. They are overlain with irregularly shaped, semi-transversely arranged, faded light-colored markings giving the limbs a somewhat banded appearance. The anterior and ventral surfaces of the forelimbs range from lemon-yellow to yellow-orange and are immaculate. The ventral surfaces of the hind limbs are orange and confluent with orange of the cloacal region. This highly partitioned coloration may provide camouflage in the leaf litter of the forest floor by disrupting the outline of the body, while the lateral lemon-yellow chest and flanks may serve as a visual signal in conspecific interactions.

Female coloration and pattern (n=1 on iNaturalist), Fig. 4A View FIGURE 4 ). Given that sexual dimorphism is common in many species of skinks as well as Sphenomorphus (e.g. Inger and Hosmer 1965; Huang 1996; Ma et al. 2018), we infer that the specimen in Figure 4A View FIGURE 4 is likely a female based on its more muted overall coloration—a condition known for other species of Sphenomorphus —and what appears to be a slightly narrower head. Overall, the female is far less colorful than the males and not nearly as boldly marked although it appears to share the same distribution pattern of colors on the body. All dorsal surfaces are generally lighter and with are overall faint reddish hue that is lacking in the males. Most noticeable is a thick, dark, wavy line on each flank that extends onto the sides of the tail and is edged by the light-colored dorsolateral and ventrolateral markings described above. This wavy line appears in the descriptions by ( Werner 1910) and is illustrated in de Rooij (1915:Fig. 75), although somewhat exaggerated on the flank.

Historical descriptions of color pattern. Boulenger’s (1890) description of the color pattern of the syntypes (one adult [SVL= 70 mm] and one juvenile [SVL= 40 mm], Fig. 5A View FIGURE 5 ) from Penang Island is brief: “Brown above, with pale reddish-brown transverse bands; a black loreal streak; a series of white spots along each side; lower parts uniform white.” That of Werner (1896) of a subadult (SVL= 60 mm [ Werner 1896] or SVL= 63 mm [ Werner 1910]) specimen from Sumatra ( Fig. 5B View FIGURE 5 ) was also short. Translated from German it reads “Above reddish-brown, with lighter brown, whitish spots and transverse bands on the sides; below dirty white. Extremities and tail yellowish.” Obviously neither author’s descriptions were based on living specimens. Werner’s (1910) later (translated) redescription of the same specimen was slightly more complete: “Upper side reddish-brown and washed-out yellowish transverse bands. A dark line from the nostril to the eye and from here, above the Tympanum extending to the base of the tail [this matches the juvenile color pattern of the Penang specimen BM BM 1946.8.2.50; Fig. 5A View FIGURE 5 ]; along the side of the body there is a dark reddish-brown wide and irregularly wavy band. Limbs above light spotted and banded; front edge of the forearm and under thigh, posterior edge of the thigh darkly spotted.” Apparently de Rooij (1915) had an additional dead specimen from Nias Island, Aceh in hand, although her description seems to be combining some of the characteristics of Boulenger’s (1890) and Werner’s (1896, 1910) descriptions: “Brown above, with pale reddish-brown cross bands; a blackish lateral streak, beginning at the rostral and sometimes broken up into spots on the posterior part of the body (her Fig. 75) by the light transverse bands and a series of white spots on the flanks, sometimes bordered towards the belly by an indistinct dark streak; labial sutures brownish. Lower parts white, sometimes a series of small black spots along each side of the belly.” Grismer’s (2011) description of the syntypes ( Fig. 5A View FIGURE 5 ) is slightly more complete and briefly includes the juvenile pattern. It is clear that none of these authors saw living material or they would have been able to discuss the vibrant and contrasting colors.

The early morphological descriptions of the Sumatran and Penang specimens ( Boulenger 1890; Werner 1896, 1910; de Rooij 1915) lack a number of important characters such as infralabial scales, chin scales in some cases and many others. Grismer (2011) provided an extensive description of the Penang specimens and that of the Indonesian specimens is in progress (Quah et al. in prep.) so as to facilitate direct comparisons in the context of taxonomy.