Dibamus tebal, Das, Indraneil & Lim, Kelvin K. P., 2009

Das, Indraneil & Lim, Kelvin K. P., 2009, A new species of Dibamus (Squamata: Dibamidae) from Pulau Simeuleu, Mentawai Archipelago, Indonesia, Zootaxa 2088, pp. 15-23 : 16-20

Dibamus tebal sp. nov.

( Figs. 1–4 )

Dibamus novae-guineae: N. de Rooj. 1922. Zoölogische Mededeelingen 6, 218.

Holotype: ZMA 15500, Sinabang (02º28’60"N, 96º22’60"E; 0 m asl), Pulau Simeuleu, Daerah Istimewah Aceh Propinsi, Republic of Indonesia ( Fig. 5 ); sex: adult male, collector: Edward Richard Jacobson; sampling details unavailable, except that a paper label associated with the specimen bears the pencilled date " VII–1913 ". Jacobson is known to have visited Simeulue in 1913 (see Fransen et al., 1997; de Rooij, 1922).

Diagnosis: A mid-sized (SVL 133.5 mm) species of Dibamus , with relatively robust body (body width 4.9% SVL), separable from congeners using the following combination of characters: postoculars two; scales around neck 24; scales around midbody 24; scales around vent 15; ventrals 186; subcaudals 42; frontonasal single; rostral suture incomplete; labial and nasals sutures complete; two pairs of preanal pores; single tibial pore located between two scales on inner distal end of each hind limb; nuchal collar or body band absent; presacral vertebrae 119; postsacral vertebrae 26; and a relatively long tail (18.7% SVL).

In showing two postoculars, the new species differs from D. bogadeki Darevsky, 1992 ( Hong Kong, eastern China), D. booliati Das and Yaakob, 2003 (northern Malay Peninsula), D. bourreti Angel, 1935 (Tam Dao, Vietnam), D. deharvengi Ineich, 1999 (Binh Châu, Vietnam), D. greeri Darevsky, 1992 ( Vietnam) , D. leucurus (Bleeker, 1860; Sumatra, Borneo, and possibly islands of southern Philippines), D. montanus Smith, 1921 (Le Bosquet, Langbian Plateau, Vietnam), D. somsaki Honda et al., 1997 (Khao Soi Dao National Park, Chanthaburi Province, Thailand) and D. tiomanensis Diaz et al., 2004 ( Pulau Tioman, Pahang, Malaysia), all of which have a single postocular. The complete and separate rostral suture distinguishes it from D. dezwaani Das & Lim, 2005 ( Pulau Nias, Indonesia). The complete nasal suture separates the new species from D. smithi Greer, 1985 (Daban, Langbian Plateau, Vietnam) and D. vorisi Das and Lim, 2003 (Borneo) , both of which show reduced nasal sutures. Finally, the contact of the first infralabial with three scales differentiates it from Dibamus novaeguineae Duméril and Bibron, 1839 (western New Guinea), D. nicobaricum (Fitzinger in Steindachner, 1867) ( Nicobar Archipelago, India), D. taylori Greer, 1985 (Sumba, Flores, Wetar and Lombok), D. ingeri Das and Lim, 2003 (Borneo) , D. kondaoensis Honda et al., 2001 (Kondao Island, Vietnam), D. celebensis Schlegel, 1858 (Sulawesi, eastern Indonesia) and D. seramensis Greer, 1985 (Seram, Makulu, eastern Indonesia), all of which have a single scale bounding Infralabial I. In showing a thick body, at ca. 5% SVL, the new species can be differentiated from congeners, which show a range of 2.4–4.4%, except D. greeri ( Darevsky, 1992; Das, unpubl.).

Description: SVL 133.5 mm, TL 24.9 mm; snout distinctly acute, slightly rounded, distinctly conical (IN/ IO ratio 0.52), projecting well beyond lower jaws; nostril laterally oriented, oval, situated closer to tip of snout than to orbit (E-N/E-S ratio 0.66); head wider than long (HL/HW ratio 0.81), not flattened (HL/HD ratio 0.89); rostral pad single, with a large number of evenly distributed sensory papillae; rostral sutures incomplete, traversing about half the distance between the edge of the maxilla and nostrils; nasal and labial sutures complete, extending from ocular to nostril; posterior border of rostral curved; frontonasal single, width 2.1 mm, depth 0.7 mm; anterior frontonasal suture with a sinous border; frontal single, width 2.8, depth 1.6 mm, x 2.3 times wider than frontonasal; interparietal single, not enlarged relative to scales on the sides or posteriorly, narrower (width 0.1 mm) than frontonasal (width 0.7 mm) and frontal (width 1.4 mm), posteriorly bordered by three subequal nuchal scales; postoculars two; supralabial single, elongate, bordering ocular ventrally; first infralabial lanceolate, length 3.3 mm (infralabial length/HW ratio 0.69), the pair separated by a smaller, elongate trapezoid mental; three scales border posterior edge of first infralabial; eyes dimly visible through ocular scale; ocular scale deeper than anterior body scales; tongue broad, fleshy and covered with transverse lamellae; tongue tip lacking lamellae, unnotched; teeth small, acute.

Body relatively robust, BW 6.6 mm (BW/SVL ratio 0.05); head distinct from neck; tail relatively long (TL/SVL ratio 0.19), tip rounded, not wider than rest of tail; tail base slightly thickened (TW/TL ratio 0.21); body scales smooth, subcycloid, including near preanal region; body and tail covered with cycloid scales that are unnotched posteriorly; scales on dorsal surface of body larger than those on tail; transverse scale rows posterior to head 25, at midbody 24, and anterior to vent 15; ventrals 186; subcaudals 42; presacral vertebrae 119; postsacral vertebrae 26 (tail complete); hind limbs present, measuring 4.8 mm in length and 1.6 mm in width (left) and 5.1 mm in length and 2.2 mm in width (right), comprising reduced (3.59 and 3.82% SVL, for left and right limbs, respectively) flap-like structures on either sides of vent, covered with four paired scales, terminating in a single scale with a rounded tip; a pair of enlarged scales on preanal region, separated by a median scale, overlapping those on sides, followed by three rows of regular-sized scales up to the anal region; preanal pores present; tibial pores located between two scales on inner distal end of hind limb; and postanal scales not reduced, relative to body scales.

Measurements (in mm): SVL 133.5; BW 6.6; TL 24.9; TW 5.3; E-N 2.1; E-S 3.2; IN 1.6; IO 3.1; HL 3.9; HW 4.8 and HD 4.4.

Colouration: Colour in life unknown. After nearly a century in preservative, dorsum is a discoloured pale brown, each scale centre dark; lacking scattered light patches; venter slightly paler than dorsum; and tip of snout, including supralabials, throat and anal region cream.

Etymology: From the Bahasa Indonesia / Malaysia ('tebal'), meaning thick, for the robust habitus.

Natural history: Nothing is on record of the natural history of this species. Species of Dibamus are fossorial and associated with lowland rainforest leaf litter. They are presumed to be predators of litter arthropods and earthworms ( Pough et al., 2001; Zug et al., 2001). The endemicity of the Mentawai Archipelago, within which Pulau Simeuleu lies, is here reemphasized with the diagnosis of the new Dibamus . A number of vertebrates are now known to be confined to these islands, which lie in close proximity to the island of Sumatra, but separated from it by deep waters (Das, 2005).

Figures

FIGURE 1. Holotype of Dibamus tebal sp. nov. (ZMA 15500). Marker = 10 mm.

FIGURE 2. Head of holotype of Dibamus tebal sp. nov. (ZMA 15500) in dorsal (top), lateral (middle) and ventral (bottom) views. Marker = 2 mm.

FIGURE 3. Anal region of holotype of Dibamus tebal sp. nov. (ZMA 15500), showing flap-like hind limbs. Marker = 1 mm.

FIGURE 4. Radiograph of holotype of Dibamus tebal sp. nov. (ZMA 15500).

FIGURE 5. A. Map of South-east Asia (top), showing location of northern Sumatra, the Mentawai Archipelago and other islands off south-west Sumatra; area enlarged indicated. B. Map of northern Sumatra (bottom), showing the location of Pulau Simeuleu, the type locality of Dibamus tebal sp. nov.