Tribolonotus choiseulensis, Rittmeyer, Eric N. & Austin, Christopher C., 2017

Rittmeyer, Eric N. & Austin, Christopher C., 2017, Two new species of Crocodile Skinks (Squamata: Scincidae: Tribolonotus) from the Solomon Archipelago, Zootaxa 4268 (1), pp. 71-87 : 81-82

Tribolonotus choiseulensis sp. nov.

Fig. 6 B,D

Holotype. AMS R127275, collected by G. Mengden, Taro Island, Choiseul Bay, near Choiseul Island , Choiseul Province, Solomon Islands, 6.7100°S, 156.3964°E, WGS 84, 20 November 1987.

Paratypes. AMS R126006–9, collected by Mike McCoy, Sumbisumbi, Choiseul Island, Choiseul Province, Solomon Islands, 6.6469°S, 156.388°E, WGS 84, 23 February 1987; AMS R127269-R127271 , collected by G. Mengden, Taro Island, Choiseul Bay, near Choiseul Island, Choiseul Province , Solomon Islands, 6.7100°S, 156.3964°E, WGS 84, 19 November 1987; AMS R127272–4, R127276–80 , collected by G. Mengden, Taro Island, Choiseul Bay, near Choiseul Island, Choiseul Province , Solomon Islands, 6.7100°S, 156.3964°E, WGS 84, 20 November 1987; BPBM 12771–2 , collected by Mike McCoy, Poroporo, Choiseul Island, Choiseul Province, Solomon Islands, 6.655°S, 156.399°E, WGS 84, 21 February 1987; BPBM 12807–12 , collected by Mike McCoy, Sumbisumbi, Choiseul Island, Choiseul Province, Solomon Islands, 6.6469°S, 156.388°E, WGS 84, 23 February 1987.

Diagnosis. A small (maximum SVL 47.8 mm) Tribolonotus diagnosable from congeners by the following combination of characters: 1) two longitudinal rows of 22–23 enlarged vertebral scales, beginning at the posterior nuchal region; 2) 42–47 ventral scale rows from mental to vent; 3) two primary temporal scales; 4) an elongate first supralabial scale, and no contact between the nasal and second supralabial scales; 5) 11–13 finger III lamellae, 20– 24 toe IV lamellae; and 6) limbs moderate in length (ForeL/SVL = 0.294–0.341; HindL/SVL = 0.498–0.532). Lateral and dorsolateral scales granular, but several longitudinal rows of spinose scales, approximately one for every enlarged vertebral scale. Tail relatively long, up to approximately 180% of SVL. Head rugose, with up to five strong keels per scale; triangular from dorsal aspect and distinct from neck. Head width variable (HW/SVL = 0.164–0.218), but broader and larger in males than females (Male HW/SVL = 0.186–0.218, mean = 0.197 versus 0.164–0.187, mean = 0.178 in females; male HL/SVL = 0.261–0.300, mean = 0.276 versus 0.242–0.273, mean = 0.257 in females; Table 2, Fig. 2 ). Two primary temporal scales, five supralabial scales, and five or six infralabial scales. A single palmar pore occasionally present at the base of finger IV. Plantar pores variably present; when present, in rows of up to six at the base of toe IV, extending back towards the insertion of toe V, and two at the base of toe III, paralleling the other row. One pair of abdominal glands present at the posterior of the abdomen, slightly anterior to the insertion of the hind limbs. Dorsal color brown with several pairs of indistinct, pale, yellowish tan paravertebral spots. Ventral coloration pale yellowish tan.

Comparisons. Tribolonotus choiseulensis sp. nov. can be distinguished from all congeners except T. parkeri sp. nov. and T. pseudoponceleti by the same characters described above for T. parkeri sp. nov.. Specifically, the combination of 1) small body size (maximum SVL = 47.8 mm), 2) two longitudinal rows of 22–23 enlarged vertebral scales, commencing at the posterior of the nape and separated from the parietal plates by granular scales, 3) elongate first supralabial scale with no suture between the second supralabial scale and the nasal, 4) two primary temporal scales, 5) 20–24 toe IV lamellae, 6) 11–13 finger III lamellae, and 7) numerous enlarged, spinose scales laterally, with approximately one enlarged scale for every enlarged mid-dorsal scale.

Tribolonotus choiseulensis sp. nov. is most similar to T. pseudoponceleti and T. parkeri sp. nov., but can be distinguished from the former in having fewer ventral scale rows (VSR = 42–47, mean = 42.864, mode = 43 in T. choiseulensis sp. nov. versus 45–53, mean = 49.009, mode = 50 in T. pseudoponceleti ; Table 3, Fig. 7 ), fewer subdigital lamellae (F3L = 11–13, mean = 12.273, mode = 12 in T. choiseulensis sp. nov. versus 13–16, mean = 14.027, mode = 14 in T. pseudoponceleti ; T4L = 20–24, mean = 22.000, mode = 22 in T. choiseulensis sp. nov. versus 21–27, mean = 23.885, mode = 24 in T. pseudoponceleti ; Table 3, Fig. 7 ), and in having shorter fore-limbs relative to hind limbs (ForeL/HindL = 0.586–0.656, mean = 0.626 in T. choiseulensis sp. nov. versus 0.612–0.737, mean = 0.672 in T. pseudoponceleti ; Table 2, Fig. 2 ). Tribolonotus choiseulensis sp. nov. is also much smaller in maximum body size than T. pseudoponceleti (maximum SVL = 47.8 mm in T. choiseulensis sp. nov. versus 76 mm in T. pseudoponceleti ). As detailed above, T. choiseulensis sp. nov. is distinguished from T. parkeri sp. nov. in having longer limbs (ForeL/SVL = 0.294–0.332, mean = 0.319 in T. choiseulensis sp. nov. versus 0.253–0.322, mean = 0.281 in T. parkeri sp. nov.; HindL/SVL = 0.498–0.521, mean = 0.510 in T. choiseulensis sp. nov. versus 0.409–0.482, mean = 0.445 in T. parkeri sp. nov.; Table 2, Fig. 2 ), and by color pattern: T. choiseulensis sp. nov. has a dark brown dorsum lighter yellowish tan markings in the form of paired, separated paravertebral spots with indistinct borders, whereas T. parkeri sp. nov. has much more extensive light dorsal markings of pale triangles, often merging to form paravertebral lines lateral to the enlarged vertebral scales.

Description of the holotype. An adult male, SVL 46.4 mm, total length 107.1 mm, with two longitudinal rows of 22 strongly keeled, enlarged vertebral scales, separated from the parietal plates by granular scales and starting at the posterior of the nuchal region ( Fig. 4 C). Dorsolateral and lateral scales granular, with several rows of approximately one larger, spinose scale per enlarged vertebral scale, but anteriorly commencing at the parietal scales. Ventral scales are weakly keeled, and totaling 42 from mental scale to nape. Head large and broad (HW = 10.1 mm; HL = 13.0 mm; HH = 6.7 mm; HW/HL = 0.777; HH/HL = 0.515), and head scales rugose with up to five moderate keels. Five supralabial scales, the first narrow and longitudinally elongate, with no contact between the second supralabial and the nasal scale; five infralabial scales and two primary temporal scales. Digits moderately long (Fing3 = 2.9 mm; Toe4 = 5.6 mm), with a moderate number of rounded subdigital lamellae (F3L = 12; T4L = 21). A single palmar pore is present at the base of finger IV of each hand. Seven plantar pores on the right foot, five at the base of toe IV and two at the base of toe III; five plantar pores on the left foot, four at the base of toe IV and one at the base of third III toe. Limbs moderately long (ForeL = 15.2 mm; ForeL/SVL = 0.328; HindL = 23.7 mm; HindL/SVL = 0.511). Dorsal coloration brown, with pale, paired paravertebral spots with vague, indistinct borders ( Fig. 4 C). Ventral coloration pale tan ( Fig 4 D). Underside of tail darker, similar to the dorsal coloration, but with some lighter mottling; underside of limbs with mottled darker brown and pale tan

Distribution. Tribolonotus choiseulensis sp. nov. is currently known only from the northwestern tip of Choiseul Island, Choiseul Province, Solomon Islands ( Fig. 1 ). However, we suspect that this apparently restricted distribution on Choiseul is an artifact of limited sampling, and that T. choiseulensis sp. nov. likely occurs in suitable habitats throughout the island.

Etymology. The specific epithet refers to the type locality on Choiseul Island, Solomon Islands, and its status as the only currently known species of the genus Tribolonotus endemic to the island.

Figures

FIGURE 1. Sampling localities of Tribolonotus choiseulensis sp. nov., T. parkeri sp. nov., and T. pseudoponceleti specimens examined in this study. Triangles indicate T. choiseulensis sp. nov., squares indicate T. parkeri sp. nov., and circles indicate T. pseudoponceleti. Filled symbols represent type localities.

FIGURE 2. Boxplots depicting differences among species and sexual dimorphism in relevant mensural characters among T. choiseulensis sp. nov., T. parker sp. nov. i, and T. pseudoponceleti. A) ForeL / SVL, B) HindL / SVL, C) ForeL / HindL, D) HW / SVL, E) HL / SVL, F) HH / SVL.

FIGURE 4. Results of principal components analyses of the morphological data. A) Plot depicting the first two principal components (PCs) based on mensural data; B) depicting the first and third PCs based on the mensural data; and C) depicting the first two PCs based on meristic data. Green triangles indicate Tribolonotus choiseulensis sp. nov., red squares indicate T. parkeri sp. nov., and blue circles indicate T. pseudoponceleti. The yellow triangle indicates the holotype of T. choiseulensis sp. nov. (AMS R 127275), yellow square indicates the holotype of T. parkeri sp. nov. (LSUMZ 93510), and the yellow circle indicates the holotype of T. pseudoponceleti (MCZ 72914).

FIGURE 6. Dorsal (A) and ventral (C) photographs of the holotype of Tribolonotus parkeri sp. nov. (LSUMZ 93510), and dorsal (B) and ventral (D) photographs of the holotype of T. choiseulensis sp. nov. (AM R 127275). Scale bars = 1 cm.

FIGURE 7. Relevant meristic characters for Tribolonotus choiseulensis sp. nov., T. parkeri sp. nov., and T. pseudoponceleti. A) Number of enlarged vertebral scales in each of the two longitudinal rows, B) number of enlarged gular + ventral scale rows (VSR), C) Finger III lamellae, and D) Toe IV lamellae.