Acanthosaura grismeri, Le & Nguyen & Nguyen & Ziegler & Do & Ngo, 2025

Acanthosaura grismeri sp. nov.

Holotype. IEBR R.6353 (Field number BMT.2023.1), adult male, collected in evergreen forest of Krong Bong , Dak Lak Province, Vietnam ( 12.4567°N, 108.63882°E, at an elevation of 989 m a.s.l.), on 18 April 2023 by H.N. Ngo and D. T. Do. GoogleMaps

Paratypes. IEBR R.6354, R.6355 , R. 6356 ( BMT.2023.2, 3, 4), adult males, collected on 18 April 2023 ; IEBR R.6357 ( BMT.2023.5), adult female, IEBR R. 6358 ( BMT.2023.6), adult male, collected on 15 October 2023; and IEBR R.6359, R.6360 ( BMT.DTD.1, 2), adult males, and IEBR R. 6361 ( BMT. DTD.3), adult female, collected on 6 December 2024. All paratypes were collected in Krong Bong forest , Dak Lak Province, near coordinates of the holotype .

Diagnosis. A moderately sized agamid lizard (SVL 77.20–91.83 mm in males, 102.70–113.09 mm in females); head triangular, relatively long (HL/SVL 0.27–0.29, HW/SVL 0.19–0.20), tail relatively long (TAL/SVL 1.21–1.44), postorbital and occipital spines present; gular pouch relatively undeveloped; 7–10 scales between nasals; 2–4 scales and four or five scales bordering mental and rostral scale, respectively; 10–12 supralabials; 11 or 12 infralabials; nuchal crest comprising 7–10 spines; dorsal crest present, underdeveloped; single row of vertebral scales followed the dorsal crest; nuchal and dorsal crests continuous, comprising small spines; lateral scales small, intermixed with large, keeled scales; keels directed backward and obliquely upward; number of subdigital lamellae 12–16 on fourth finger and 20–24 on fourth toe ( Table 3); black nuchal collar present; dorsum with black bands on some males but absent in others; black patch extending from eye to anterior edge of tympanum absent; color of dorsal surface green in males but dark-brown in females with scattered black spots; black or brown thick lines radiate upward and ventrally from orbit, and a faint white line edged posteriorly in brown extends from eye to corner of mouth.

Description of holotype. Adult male ( Fig. 2 View FIGURE 2 ), snout-vent length 83.72 mm; tail complete, 114.78 mm in length (TAL/SVL 1.37); head triangular in dorsal view, 23.35 mm in length (HL/SVL 0.28), 16.20 mm in width (HW/HL 0.69), 14.05 mm in height (HH/HL 0.60); snout moderately long (SL 9.03 mm, SL/HL 0.39); loreal region steeply sloping anteriorly; a row of 13 large scales along canthus-rostralis edge, forming a large projecting shelf extending above eye, terminating in a notch anterior to postorbital spine; rostral moderate in size, 2.4 times wider than high, trapezoidal, bordered laterally by first supralabials and posteriorly by five smaller scales; nostril round, surrounded by two prenasals anteriorly, three postnasals posteriorly, two subnasals and two supranasals; nasals separated from each other by 8 internasals; orbit large (ORBIT/HL 0.37); interorbital, prefrontal and frontal scales slightly keeled; small postorbital spine ( 0.81 mm); a row of five (left)/four (right) large keeled scales on each side, extending from postorbital margin to above tympanum; a prominent spine above tympanic margin; occipital spine short ( 1.29 mm), on lateral margin of nape, surrounded by a rosette of five small lanceolate scales; tympanum exposed, elliptical, surrounded by very small keeled scales; supralabials 12/11 (L/R), rectangular, scales in center of series largest, slightly decreasing in size posteriorly; infralabials 12/11 (L/R), rectangular, similar in size; gular scales sharply keeled and spinose with a larger midventral row; mental pentagonal, edged by two postmental scales and two infralabials; a narrow dewlap present, gular pouch undeveloped; nuchal crest composed of one small and seven medium-sized, elongated, dagger-like scales, decreasing in size posteriorly, bordered on each side by two rows of large, flat, keeled, triangular scales; nuchal crest continuous with smaller dorsal crests at base of nape, diastema absent; vertebral crest comprising a single row of enlarged, keeled, pointed scales, ending at the base of tail.

Body gracile, triangular in cross-section; dorsal scales small, intermixed with large keeled scales, arranged in transverse rows; flanks covered by small scales, randomly intermixed with small keeled scales projecting obliquely posteriorly; scales in pectoral region and abdomen larger than those on dorsum, keeled, spinose, arranged in semitransverse rows; ventral scales keeled, larger in size posteriorly; limbs relatively long, dorsal surface of fore- and hind limbs covered with keeled scales, larger than ventral scales; five digits on manus; subdigital scales keeled, subdigital lamellae 15/16 (L/R) on the fourth finger; five digits on pes; subdigital scales keeled, subdigital lamellae 24/23 (L/R) on the fourth toe; tail covered by small keeled scales, directed posteriorly.

Coloration in life. Dorsal surface of head light-brown to green with a short poorly-demarcated transverse band of light-green across the orbital region; occipital surface light lime green; black or brown thick lines radiate dorsally and ventrally from orbit; upper and lower lips lime green; lateral side of neck lime green to white; nuchal crest spines black to orange (fourth and seventh spines), black (second and fifth spines), light yellow at the top and black (sixth spine) and green (first spine and pre-spines); iris dark-brown; tongue light orange; dorsal surface of body light-lime green with four brownish black rhomboidal bands centered in the vertebral region extending from nape to sacrum; dorsal surface of limbs light green, white patches on elbows and knees present; lateral edges of gular region pearl white, remaining gular region light colored; dorsal surface of limbs light green, faintly speckled; ventral surfaces of limbs lime green laterally and white ventrally; black and light green rings on tail, becoming indistinct posteriorly ( Figure 2 View FIGURE 2 ).

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Coloration in preservative. Dorsal surface of body fades from light green to dark grayish blue while retaining the brown markings and other patterns ( Figure 3 View FIGURE 3 ).

Variation. Morphometric and meristic data for the type series are provided in Table 3. The new species displays distinct sexual dimorphism with females having significantly larger body, head and limbs (mean SVL: 107.89 ± 5.2 mm versus 82.8 ± 4.46 mm; HL: 29.92 ± 1.52 mm versus 23.33 ± 1.31 mm; HW: 21.72 ± 0.89 mm versus 16.01 ± 0.76 mm; HH: 17.3 ± 0.13 mm versus 13.68 ± 0.49 mm; FOREL: 33.08 ± 3.39 mm versus 27.09 ± 1.98 mm; HINDL: 44.2 ± 2.98 mm versus 37.87 ± 1.81 mm). Females are characterized by being predominantly dark brown with scattered black or green mottling, distinct from males showing the light lime-green with brownish black rhomboidal bands on the dorsal surface ( Figure 4 View FIGURE 4 ).

Some males have brownish black bands on the dorsal surface, but they are absent in other males ( Figure 5 View FIGURE 5 ). Ventral surface of head in males is pearl white but in females it is light brown with dark spots, transitioning to dark orange near the neck. Eye margins of females are characterized by black and faint yellow-green radial patterns that are absent in males. Iris dark brown in males but light orange in females. In males, the dorsal surface of body and limbs are light green in the holotype and some males have brownish-black bands on the back that may be absent in other males and females. The dorsal surfaces of body and limbs in females are dark brown with scattered black or green spots and patches.

In preservative, both male and female specimens lose the green coloration, and males become more grayishblue while females do not ( Figure 6 View FIGURE 6 ).

Etymology. The specific epithet is dedicated to Prof. Dr. L. Lee Grismer (La Sierra University, USA) in recognition of his great contributions to herpetological research in Southeast Asia.

Distribution. Acanthosaura grismeri sp. nov. is currently known from Krong Bong forest, Dak Lak Province, in the Central Highlands of Vietnam ( Fig. 7 View FIGURE 7 ).

Natural history. Lizards were collected at elevations above 700 m a.s.l. in evergreen forest ( Figs. 7 View FIGURE 7 ; 8 View FIGURE 8 ). They were observed during night surveys, clinging to, and sleeping in shrubs or on thin trunks of small trees beneath dense forest canopy. The height of occupied perches ranged from 0.3–1 m above ground. We frequently encountered lizards during April 2023 and December 2024 in the rainy season, but they were rarely observed during October 2023 in the dry season.

Comparisons: Detailed comparisons of Acanthosaura grismeri sp. nov. with other species of Acanthosaura are presented in Table 4. With respect to its closest congeners, A. cuongi and A. coronata , Acanthosaura grismeri sp. nov. differs from them as follows:

The new species differs from A. coronata Günther, 1861 by having a longer body (maximum SVL 113.09 mm versus 86.1 mm) and a longer head (HL 22.16–31.44 mm versus 14.4–16.3 mm), a larger orbit and tympanum (ORBIT 8.39–10.72 mm versus 6.9–7.5 mm, and TD 3.18–5.34 mm versus 1.7–2.8 mm, respectively), the presence of dorsal and nuchal crest spines, more subdigital lamellae on the fourth toe (TO 20–24 versus 17–19), fewer scales bordering the rostral scale (RS 4–5 versus 9), and fewer scales between the nasal and the rostral (NR 1–2 versus 3–4).

Acanthosaura grismeri sp. nov. differs from A. cuongi Ngo, Le, Nguyen, Nguyen, Nguyen, Phan, Nguyen, Ziegler & Do, 2025 by having fewer scales bordering the rostral scale (RS 4–5 versus 5–7), lacking a diastema between nuchal and dorsal crests and a black eye patch ( versus present), and having only one row of enlarged, keeled, pointed scales on the vertebral scales ( versus two rows) ( Fig. 5 View FIGURE 5 ).