Dicrodon Duméril and Bibron

Harvey, Michael B., Ugueto, Gabriel N. & Gutberlet, Ronald L., 2012, 3459, Zootaxa 3459, pp. 1-156 : 116-117

Dicrodon Duméril and Bibron

Figure 68

Dicrodon Duméril and Bibron 1839: 137 . Type species Dicrodon guttulatum Duméril and Bibron by monotypy.

Diagnosis.— Dicrodon and Teius are the only teiids with transversely oriented, bicuspid teeth. Unlike Teius (characters in parentheses), Dicrodon lacks an apical basin on its hemipenis (basin present) and has fused frontoparietals (paired), a fifth toe with four phalanges (fifth toe vestigial, reduced to small nub), and sharply keeled distal digital lamellae under the fourth toe (weakly keeled or smooth). In addition, the first supraocular usually broadly contacts the second supraocular (separated by complete row of granular scales) in Dicrodon , although this character shows some regional variation ( Fugler 1973).

Content.— Dicrodon guttulatum guttulatum Duméril and Bibron , Dicrodon guttulatum holmbergi Schmidt , Dicrodon heterolepis (Tschudi) .

Definition.—Medium lizards reaching 163 ( Dicrodon guttulatum ) mm SVL; tail 2.2–2.8X ( Table 12) as long as body; posterior maxillary and dentary teeth transversely compressed, bicuspid; pupil reniform.

Prefrontal usually in contact with nasal, separated from or in contact with first supraciliary; frontal entire, with longitudinal ridge in center of scale, its posterior suture contacting third supraocular; scales of frontoparietal region smooth, outwardly convex to flat ( Dicrodon heterolepis ) or with weak key-hole shaped depression ( D. guttulatum ); frontoparietals fused; parietals arrayed in oblique rows; interparietal entire; medial pair of enlarged occipitals absent; occipitals 10–16, usually subequal to first row of dorsals; supratemporals slightly to moderately enlarged, separated from parietals by one or more scales.

Rostral groove present; nostril oval and oriented anteroventrally, positioned anterior to and not touching nasal suture; loreal single; supraoculars eight; first supraocular entire, usually larger than fourth supraocular, usually broadly contacting second supraocular; circumorbital semicircles consisting of 21–30 small scales, extending to posterior margin of first supraocular or point medial to second supraocular; supraciliaries subequal, 11–15, separated from supraoculars by 1.5–3 rows of 43–84 granular scales; first supraciliary contacting or separated from first subocular; angulate keel extending from first subocular to elongate subocular below eye; suboculars four; first subocular separated from supralabials by scale inserted between suboculars and loreal or, less frequently, by anterior expansion of second subocular; patch of distinctly enlarged scales in front of auditory meatus; auricular flap and preauricular fold absent.

Supralabials 12–14; first supralabial smaller than second, its ventral margin curved to “toothy”; infralabials 10–13; first pair of chinshields broadly contacting or partially (rarely completely) separated from infralabials, forming medial suture greater than or equal to half their length; interangular sulcus absent; anterior gulars 16–26; gular patch absent; posterior gulars 7–20; intertympanic sulcus absent; larger anterior gulars undergoing sharp transition to smaller posterior gulars at intertympanic crease; mesoptychials moderately enlarged; gular fold lacking serrated edge.

Dorsals smooth ( Dicrodon guttulatum ) or keeled ( D. heterolepis ); scales on flank subequal to ( D. guttulatum ) or much smaller than ( D. heterolepis ) middorsals, not projecting laterally, supported by small apical granules; scales on rump much smaller ( D. guttulatum ) to slightly smaller ( D. heterolepis ) than proximal subcaudals; scales of chest large and flat; pectoral sulcus absent; ventrals smooth, in 29–34 transverse and 8–10 longitudinal rows; lateral-most ventrals flanked by small scales (i.e., ventrals not gradually decreasing in size on flanks); preanals 4–5; preanal plate present, bordered by subtriangular scales; preanals one-half as large to larger than scale anterior to them; preanal spurs, postcloacal buttons, and postanal plates absent; scales on dorsolateral edge of tail like those on top and sides, denticulate edge and dorsolateral crests absent; caudal annuli complete; proximal subcaudals smooth.

Enlarged scales of brachium connected by continuous band of enlarged subtriangular plates on dorsal surface of arm; preaxial brachial scales 1–2X as wide as long, extending to or beyond center of arm; postaxial brachial scales 1–2X as wide as long (not enlarged in some Dicrodon guttulatum ), restricted to patch near elbow; antebrachial scales enlarged and smooth, narrowly ( D. guttulatum ) or broadly ( D. heterolepis ) separated from preaxial brachial scales; postaxial antebrachial scales slightly enlarged ( D. guttulatum ) to granular ( D. heterolepis ); subdigital lamellae of hand homogeneous in size, 15–21 under fourth finger.

Prefemorals 7–11; femoral and abdominal pores 26–44, in continuous row on each side (abdominal pores not separated from femoral pores by gap); each compound pore-bearing scale consisting of partially fused prefemoral or abdominal scale and 2–6 granular scales; 3–6 scales separating right and left pore rows; scales at heel small and numerous; tibiotarsal shields and spurs absent; lamellae under fourth toe 29–41; distal lamellae of fourth toe sharply keeled; continuous low serrate row of scales separating subdigital and supradigital lamellae of toes 2–4 ( Dicrodon guttulatum ) or 2–5 ( D. heterolepis ); noticeably enlarged postaxial scales between fourth and fifth toe absent; fifth toe reduced, base of its claw not passing level of skin between third and fourth toes when adpressed.

β- keratin containing layers of dorsal scales folded into macrohoneycomb; dorsal and caudal scales with one subterminal lenticular scale organ; ventrals lacking scale organs; generation glands present.

Snout same color as dorsal head scales; adult male Dicrodon heterolepis often with sides of head, chin and sometimes throat pink or whitish but color not restricted to snout. In juveniles, light vertebral stripe absent ( D. guttulatum ) or present and solid, although often breaking posteriorly ( D. heterolepis ); light paravertebral stripes absent ( D. guttulatum ) or present and solid, although fading towards head ( D. heterolepis ); dark dorsolateral field absent or only faintly indicated; dorsolateral light stripe solid, extending to tail; dark lateral field solid ( D. heterolepis ) or with light spots within it ( D. guttulatum ); upper lateral light stripes mostly solid, extending to groin ( D. heterolepis ) or broken, especially anteriorly ( D. guttulatum ); lower lateral light stripe absent in D. guttulatum (condition in D. heterolepis could not be observed); thigh lacking light spots. In adult males, flanks with light spots; presence or absence of turquoise ventrolateral spots could not be observed; venter immaculate, lacking melanic areas; juvenile dorsal color pattern present in adult males with moderate modification.

Hemipenis with pair of taβ- like and smooth apical awns; apical papillae and apical basin absent; asulcate expansion pleat well-developed, interrupting about 17 distal laminae; discontinuous distal laminae absent; zero ( Dicrodon guttulatum ) or about six ( D. heterolepis ) laminae proximal to expansion pleat; basal papillae absent.

Etymology.— Dicrodon is a masculine noun in the nominative singular derived from the Greek prefix di and noun odontos. The name refers to the bifid posterior teeth characteristic of this genus.

Distribution.— The two species of Dicrodon occur west of the Andes in arid environments of Ecuador and Peru.