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Adercosaurus vixadnexus MYERS & DONNELLY, 2001

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Higher TaxaGymnophthalmidae (Ecpleopodinae), Sauria, Gymnophthalmoidea, Squamata (lizards)
Common Names 
SynonymAdercosaurus vixadnexus MYERS & DONNELLY 2001
Adercosaurus viadneus [sic] — BARRIO-AMOROS & BREWER-CARIAS 2008 
DistributionVenezuela (NW Tepuis region)

Type locality: wet gallery forest on Cerro Yutajé, 1700 m elevation (5°46’N, 66°08’W), Amazonas, Venezuela.  
TypesHolotype: EBRG 3126 (field no. CWM 19809), an adult male; collected February 25, 1995, AMNH–TERRAMAR Expedition. See locality 1 on map (fig. 1). 
DiagnosisDiagnosis: Small lizards, maximum size probably less than 80 mm SVL, with tail probably less than twice body length. Tongue anteriorly and posteriorly bearing oblique, anteriorly converging plicae, with intervening midsection of imbricate scalelike papillae; three pairs of nonswollen chrevron-shaped infralingual plicae. Pterygoid teeth present. Phalangeal formulae 2-3- 4-5-3 for hands, 2-3-4-5-4 for feet. Hemi- penis lacking spines or spinules, symmetrically bifurcate, with thickened, lobate apical discs; asulcate side of hemipenis with encircling nude ridges. Head scales smooth. Nasal scales separated by rostral and undivided frontonasal. Loreal separated from labials by frenocular. Supraoculars separated from eyelids by a complete superciliary series; anterior superciliary large, not expanded dorsally. Translucent palpebral disc composed of about six vertical panes. Frontoparietals medially in point contact. Interparietal longer than parietals, their common sutures forming a jagged line across rear of head. Tympanum slightly recessed, lightly pigmented. Single postmental scale followed by three pairs of genials in contact with labials. Anterior gular crease, incomplete guttural fold, and collar fold all conspicuous. Paramedian gulars enlarged, in short double row. Dorsal and lateral scales elongate with parallel sides, hexagonal, in transverse rows only; dorsals sharply keeled, strongly mucronate, laterals becoming less so. Lateral fold absent, a gradation between lateral and ventral scales; median ventrals smooth, rectangular, gently rounded posteriorly, subimbricate, forming both transverse and longitudinal rows. Pre-anal scales in two rows. Femoral pores and preanal pores on same line. Limbs pentadactyl, all digits clawed; subdigital lamellae divided; base of pollex with enlarged thenar scales having produced median keels. Caudal scales similar to body scales, in uninterrupted annuli, no paramedian series of supracaudals along a vertebral suture.

In having oblique plicae on the anterior as well as the posterior part of the tongue, Adercosaurus seems to stand apart from all other microteiids (including Arthrosaura) except Alopoglossus, Ecpleopus, Ptychoglossus, and Riolama, but it stands with Ecpleopus and Riolama in having the lingual plicae interrupted by a midsection of scalelike papillae. Among these genera, Adercosaurus most closely resembles Arthrosaura and some Ptychoglossus in habitus and body scalation, but those two genera and Alopoglossus are distinctive in having the posterior margins of the parietals and interparietal forming a more- or-less straight line across the rear of the head (interparietal posteriorly projecting, forming a jagged or irregular line in Adercosaurus and Riolama, a gently rounded line in Ecpleopus). Ecpleopus differs from all in having hexagonal ventrals that do not form longitudinal rows, the ventrals being being arranged in transverse rows only. The endemic tepui genus Riolama differs from Adercosaurus in lacking a claw on the first finger, 22 in having the subdigital lamellae mostly undivided, and in having smooth lateral scales that are smaller than the keeled dorsals.
The primarily Andean genus Anadia also reaches the tepuis, but it differs most conspicuously from other tepui microteiids in having a tight covering of nonmucronate (and usually smooth) dorsal scales that are juxtaposed or only subimbricate, as well in having a very long tail and a relatively attenuated, flat-topped snout that give it a distinctive aspect. Anadia evidently differs from Adercosaurus in hemipenial morphology (comblike rows of spinules in Anadia) and in the dorsal surface of the tongue (scalelike papillae anteriorly), but summary data for Anadia have not been published. Anadia, however, has been characterized as having (in 9 species) 6–10 swollen infralingual plicae (Harris, 1985), which differs from the three thin (nonswollen) infralingual plicae in Adercosaurus. 
CommentType species: Adercosaurus vixadnexus MYERS & DONNELLY 2001 is the type species of the genus Adercosaurus MYERS & DONNELLY 2001.

Subfamily: the subfamilial classification of this genus is still unresolved (T. Doan, pers. comm., 2 Jun 2014).

For diagnostic morphological characters distinguishing Marinussaurus, Amapasaurus, Anotosaura, Arthrosaura, Colobosauroides, Dryadosaura,Ecpleopus, Kaieteurosaurus, Leposoma, and Pantepuisaurus see Table 2 in PELOSO et al. 2011.

Abundance: only known from the type specimen (Meiri et al. 2017). 
EtymologyNamed after the Latin adverb vix (barely, hardly) and the passive past participle adnexus (tied together or joined, connected), calling attention to the possibly diagnostic point contact of the frontoparietal plates (fig. 34 in MYERS & DONNELLY 2001).

The genus was named after the Greek aderkes (something unexpected or unseen), and sauros—an unexpected lizard. Gender masculine. 
  • Barrio-Amorós, César L. & Brewer-Carias, Charles 2008. Herpetological results of the 2002 expedition to Sarisari–ama, a tepui in Venezuelan Guayana, with the description of five new species. Zootaxa 1942: 1-68 - get paper here
  • Meiri, Shai; Aaron M. Bauer, Allen Allison, Fernando Castro-Herrera, Laurent Chirio, Guarino Colli, Indraneil Das, Tiffany M. Doan, Frank Glaw, Lee L. Grismer, Marinus Hoogmoed, Fred Kraus, Matthew LeBreton, Danny Meirte, Zoltán T. Nagy, Cristiano d 2017. Extinct, obscure or imaginary: the lizard species with the smallest ranges. Diversity and Distributions - get paper here
  • Myers, C. W. & M. A. DONNELLY 2001. Herpetofauna of the Yutajé-Corocoro Massif, Venezuela: second report from the Robert G. Goelet American Museum - Terramar Expedition to the Northwestern Tepuis. Bull. Amer. Mus. Nat. Hist. (261): 1-85 - get paper here
  • Myers, Charles W. Rivas Fuenmayor, Gilson; Jadin, Robert C. 2009. New species of lizards from Auyantepui and La Escalera in the Venezuelan Guayana, with notes on "microteiid" hemipenes (Squamata, Gymnophthalmidae). American Museum Novitates (3660): 1-32 - get paper here
  • RIVAS, GILSON A.; CÉSAR R. MOLINA, GABRIEL N. UGUETO, TITO R. BARROS, CÉSAR L. BAR- RIO-AMORÓS & PHILIPPE J. R. KOK 2012. Reptiles of Venezuela: an updated and commented checklist. Zootaxa 3211: 1–64 - get paper here
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