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Nactus heteronotus (BOULENGER, 1885)

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Higher TaxaGekkonidae, Gekkota, Sauria, Squamata (lizards: geckos)
Common NamesE: Central Savanna Slender-toed Gecko 
SynonymGymnodactylus heteronotus BOULENGER 1885: 41
Nactus heteronotus — ZUG 2020: 65 
DistributionPapua New Guinea (coastal savannas of the Central Province and the National Capital Province)

Type locality: “Hall Sound”  
ReproductionNactus pelagicus is a composite of unisexual [parthenogenetic] and bisexual populations. Note however that Zug and Moon (1995) recognized Nactus pelagicus as the asexual species for the populations in southern Vanuatu and elsewhere in Oceania, and N. multicarinatus for the bisexual species from Vanuatu and the southern Solomon Islands. 
TypesHolotype. AMS R31934 
DiagnosisDefinition. A bisexual taxon of geckos (Gekkoninae) of small to moderate adults (♀♀ 39–47 mm, ♂♂ 37–48 mm SVL) with keeled subcaudals, usually moderate postmental scales (6–20, median 12), no postmental-infralabial contact (PmLab 0), low number of dorsal tubercle rows (11–14) and moderate number of tubercles (19–32, median 24) in parasagittal row (TubRow), tubercles present on dorsal surface of thigh and crus (uncommonly on only crus), and few precloacal pores in males (5, 0–7), females usually lack pores (0, 0–1). Diagnostic summary in Table 8 (n = 39, Zug 2020).

Variation. Females and males display slight metric differences (adult ♀♀ 43.3, 38.5–47.1 mm; adult ♂♂ 42.1, 37.2– 47.7 mm SVL), although sharing similar proportions (total adult sample): TrunkL/SVL 42.7%, 33%–49%; HeadL/SVL 26.2%, 20%–28%; HeadW/SVL 18.5%, 14%–21%; HeadW/HeadL 70.9%, 62%–83%; EyeD/SVL 6.4%, 5%–9%; EyeD/HeadL 24.8%, 20%–36%; NarEye/HeadL 31.4%, 28%–36%; Interorb/HeadL 30.0%, 22%–44%; SnW/HeadL 16.2%, 14%–24%.
Typical head scale pattern of small, granular scales except for those bordering nares and mouth. Snout with large rostral scale bearing middorsal cleft posteriorly; supranasals moderate sized, usually in contact on midline or separated by small granular scale (internasal); large supralabials (3, 3–4) and infralabials (3, 2–4) in front of anterior edge of orbit, first supraand infralabial largest of respective series. Chin with large trapezoidal mental and moderate postmentals (Postm = 12, 6–20) and with no genial scale between postmental and first supralabial (0 PmLab); dorsally, trunk with 13, 11–14 (DorsTub) enlarged tubercles transversely on dorsum and with 24, 19–32 tubercles (TubRow) longitudinally along trunk; 8, 8–9 tubercle rows transversely between hindlimbs (TubHip). Enlarged tubercles on crus and femur variable (TubHindl = 1 or 2) and possibly sexually dimorphic as 23% of males have tubercles on only crus compared to 8% of the females. Tail with small uniform scales dorsally and laterally, ventrally variable with uniform, small keeled scales (Subcaud = 0). Usually, pair of cloacal spurs (2, 0–2 CloacS) on each side. Ventral scales from chin to vent small, granular, somewhat larger on chest and abdomen. Precloacal pores, males 3–7, females usually lack pores, 0–1. Forefoot with narrow digits, their lengths usually 3≈4>2≈5>1; 14, 11–15 lamellae beneath fourth digit (4FingLm), 6, 4–7 scale rows on palm; hindfoot with narrow digits, their lengths 4>3>5>2>1 or 3≈4>2≈5>1; 18, 16–20 lamellae beneath fourth toe (4ToeLm) (Zug 2020).

Coloration in life from F. Kraus’s photo of Moresby area specimen. Dorsal background brown from snout to posterior trunk becoming brownish white. This light color evident ventrolaterally from throat to and onto tail. Top of head vaguely marked with darker-brown moderately broad canthal white stripe onto anterior edge of eye, bordered below by white and dark-brown upper lip; moderately broad dark-brown postorbital stripe to ear. Dorsally, trunk with 6 irregular dark-brown transverse bars extending onto base of tail. In alcohol, color and pattern match the general description of the topotype. The top of the head is usually unicolor or indistinctly mottled; the sides of the head range from unicolor to possession of distinct dark preand postocular stripes with broadly barred lips. The dorsal trunk pattern of transverse bars varies from faded to dark, but all bars are irregularly formed without distinct borders; in some the dark bars are distinctly edged posteriorly in cream and range from 5 to 6 bars between shoulders to sacrum. Forelimbs are usually uniformly medium brown; hindlimbs (thigh) are unicolor to faintly mottled with dark brown dorsally. Underside is unicolor light brown to cream. Unregenerated tails are distinctly banded in light tan to cream and brown (Zug 2020). 
CommentSynonymy: this species has been considered as a synonym of N. pelagicus for most of recent history until it was revalidated by Zug 2020. 
EtymologyBoulenger did not explain his choice of heteronotus as a replacement name, presumably different dorsal trunk scales from the Greek heteros (“other,” “different”) and notos (“back”). 
  • Boulenger, G.A. 1885. Catalogue of the lizards in the British Museum (Nat. Hist.) I. Geckonidae, Eublepharidae, Uroplatidae, Pygopodidae, Agamidae. London: 450 pp. - get paper here
  • Zug, George R. 2020. Diversity in Pacific Slender-Toed Geckos, Nactus pelagicus Complex (Reptilia: Squamata), of New Guinea and Adjacent Islands. Smithsonian Contributions to Zoology, (651): x + 92 pages - get paper here
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