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Uracentron flaviceps (GUICHENOT, 1855)

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Higher TaxaTropiduridae, Iguania, Sauria, Squamata (lizards)
Common NamesE: Tropical Thornytail Iguana
Portuguese: Lagarto-Espinhoso 
SynonymDoryphorus flaviceps — GUICHENOT 1855
Doryphorus castor COPE 1871: 556
Uranocentrum flaviceps — O'SHAUGHNESSY 1881
Uracentron flaviceps — BOULENGER 1885 (?)
Urocentron flaviceps — BOULENGER 1885: 183
Urocentron castor — BOULENGER 1885: 184
Urocentron flaviceps — MERTENS 1925: 75
Uracentron flaviceps — DUELLMAN 1978: 208
Tropidurus flaviceps — FROST 1992
Uracentron flaviceps — AVILA-PIRES 1995: 216
Tropidurus flaviceps — HARVEY & GUTBERLET 2000
Uracentron flaviceps — FROST et al. 2001
Tropidurus flaviceps — LEHR 2002: 203
Uracentron flaviceps — PIANKA & VITT 2003: 135 
DistributionNW Brazil (Amazonas, Rondonia, Acre), SE Colombia, E Ecuador, E Peru, Brazil, Bolivia ?

Type locality: Sarayacu (Pastaza), Ecuador, Peru.  
TypesHolotype: MNHN-RA 6882 (fide Avila-Pires 1995: 216, but indicated in MNHN catalogue as holotype of U. azureus)
Syntypes: ANSP 11303, Ecuador, Pebas; MCZ 12440, Huanuco, Peru [Doryphorus castor] 
DiagnosisDiagnosis: In addition to the generic characteristics, it has a strongly depressed tail with 31-37 transverse rows of scales; 68-85 scales around midbody; 81-98 middorsal scales between nape and posterior margin ofhind limbs. In life predominantly brown, with or without a light and black collar, and light spots (Avila-Pires 1995: 216).

Description. Tropidurid with maximum SVL in males of 130 mm (MHNP 6882), in females of 95 mm (Rand, 1982). Head 0.22-0.26 (0.24 ± 0.01, n= 15) times SVL, 1.1-1.4 (1.27 ± 0.08, n= 15) times as long as wide, 1.2-1.4 (1.27 ± 0.06, n= 15) times as wide as high. Snout broadly rounded, canthus rostralis anteriorly rounded, posteriorly angulate. Neck, due to presence of lateral folds, as broad as, or slightly broader than, head and anterior part ofbody. Body moderately depressed. Limbs well developed, forelimbs about half (0.48 ± 0.01, n= 4) the SVL, hind limbs about 0.6 (0.60 ± 0.03, n= 4) times, tibia 0.17-0.20 (0.18 ± 0.01, n= 15) times. Tail short, wide, depressed and spinose; 0.50-0.65 (0.57 ± 0.04, n= 15) times SVL, 2.7-3.4 (3.03 ± 0.26, n= 10) times as long as wide, 2.2-2.9 (2.68 ± 0.40, n= 9) times as wide as high (both measurements at widest level of tail).
Tongue villose, with a round, nicked tip. Anterior teeth conical, posterior teeth tricuspid, with median cuspid much higher than lateral ones.
Rostral bandlike, two and a half to three times as wide as deep, hardly visible from above. Postrostrals 3-5, usually four, flat; they form a continuous row with lorilabials. Scales on snout relatively large, but with some variation in size, irregularly polygonal, juxtaposed, with a slightly to moderately convex, rugose surface. Scales across snout between posterior (or single) canthals 4-6. Nasal large, undivided, medial to canthus rostralis, and extending toward the postrostral/lorilabial series, with which it may have a relatively narrow to a broad contact. Nostril directed anterodorsally, in the upper posterior part of nasal. Canthals 1-2, anterior one, when present, usually extending toward loreal region and in contact with lorilabials. Supraorbital semicircles inconspicuous or with 8-12 scales, in contact or separated medially. Supraoculars 4-7, transversely enlarged, bordered medially by two rows of scales about as long as wide, and laterally by an incomplete row of scales which are wider than long and, in some specimens, another incomplete row of small scales; a group of small scales is present anteriorly; adjacent to supraciliaries, a row of rectangular, flat, small scales. Supraciliaries 7-11, anterior ones moderately elongate and each overlapping the scale posterior to it, posterior supraciliaries juxtaposed or slightly overlapping the scale immediately anterior. Interparietal much larger than adjacent scales, irregular in shape. Parietal eye absent. Parietal region with moderately small, irregularly polygonal, juxtaposed to slightly imbricate scales, with a rugose and sharply convex surface. Loreal region with a few relatively large, irregular, rugose and sometimes keeled scales, bordered ventrally by the row of lorilabials. Suboculars 2-4, mostly three, with a keel along their upper margin. Posterior subocular distinctly larger and in contact with supralabials; it marks the end of lorilabialseries. Supralabials 5-6, rarely four, posterior one longest and below centre of eye. They are followed by scales similar to adjacent temporal scales, or by two to four enlarged scales. Temporal scales relatively small, conical to trihedral, with a distinct keel. Ear-opening large, in larger specimens bordered anteriorly by transversely compressed and sharply keeled scales.
Mental from about as wide as, to narrower than, adjacent infralabials, and a little longer. Postmentals three (two, asymmetrical, i n A M N H 57207). Infralabials 5-6, exceptionally seven, last or one but last below centre of eye. Scales on chin juxtaposed, medially small, elongate, polygonal to oval, convex to broadly keeled; near infralabials distinctly larger, polygonal, slightly convex. A midventral sulcus may be distinct. Posteriad scales change gradually into gulars. Gular region anteriorly with swollen ventrolateral areas, with slightly imbricate, quadrangular to hexagonal, convex, and sometimes feebly keeled scales, which become flatter medially and smaller posteriorly. Gular and antegular folds present, with relatively small, rhomboid, flat, imbricate scales between them. They extend laterally into, respectively, the oblique neck and the antehumeral folds. All dorsal head scales, infralabials, and part of the scales on chin with very minute tubercles (scale organs) widespread on their surface.
Scales on nape small, conical to trihedral, keeled; in some specimens (especially larger ones) shortly mucronate. They gradually change into dorsals. Dorsals distinctly keeled and slightly imbricate, anteriorly smaller and low-trihedral to flat, posteriorly slightly larger and flat; 81-98 (92.1 ± 4.8, n= 15) middorsal scales from nape to posterior margin of hind limbs. Toward the flanks scales decrease slightly in size. Ventrals flat, imbricate, smooth to slightly keeled, on chest rhomboid, posteriorly quadrangular; in 51-67 (59.8 ± 4.8, n= 15) transverse rows (from posterior gular fold to anterior margin of hind limbs). Transition between scales on flanks and ventrals gradual. Scales around midbody 68-85 (79.1 ± 5.1, n= 15). Preanal plate mostly with rhomboid, imbricate, smooth scales, about as large as ventrals and separated from them by smaller scales.
Scales on dorsal surface of tail relatively large, imbricate, keeled and mucronate, in longitudinal and 31-37 (35.3 ± 1.8, n= 10) distinct transverse rows. At edge of tail the keels develop into spines. On ventral surface, scales near base of tail small, rhomboid to quadrangular, smooth, imbricate. Distally they become larger and slightly keeled (distinctly keeled near tip), arranged in transverse rows continuous with the dorsal ones. Nine to 11 scales dorsally, 11-14 ventrally, across widest section of tail.
Forelimbs with rhomboid,imbricate scales, smooth on posterior and part of ventral aspects ofupper arms, and ventral aspect of forearms, keeled elsewhere. Hind limbs with similar scales, smooth on ventral aspect of thighs, and ventral and posterior aspects of lower legs, keeled elsewhere. Subdigital lamellae proximally multicarinate, distally tending to be uni- or tricarinate; 29-35 (31.5 ± 1.6, n= 30,15 specimens) lamellae under fourth finger, 31-36 (33.2 ± 1.5, n= 29,15 specimens) under fourth toe.
Some variation in colour pattern exists, which in part seems to be sexual/age linked (Etheridge, 1968: 56; Fugler & Schwaner, 1968: 253), in part geographically determined (Dixon & Soini, 1975: 36,1986:42). MPEG 15988, a juvenile or halfgrown female, in life had dorsal part of head salmon (106) with black spots; a black collar, followed by a buff-yellow (53) one; body and limbs dusky-brown (19), densely covered with buff-yellow (53) flecks. Ventral region cream-colour (54) under head and chest, changing into pale salmon (106) on posterior part of belly; under head with some brown spots. Tail dorsally dusky-brown, ventrally peach-red (94). Iris very dark, difficult to distinguish from pupil. Tongue pinkish.
Descriptions of colour in life were given by Etheridge (1968), Fugler & Schwaner (1968; based partially on specimens in alcohol, partially on alive material), and Dixon & Soini (1975,1986). Guichenot (1855: pi. HI) presented a colour plate of the holotype.
In preservative, most specimens with dorsal surface of head bluish-grey, buff-yellow or dark tan, with dark (blackish) spots; a dark collar (of the same basic colour as back) is present on nape, bordered anteriorly and posteriorly by a light band, the anterior one narrower (colour similar to that of head, or whitish); the light bands may be bordered anteriorly (in part) by a blackish stripe, posteriorly by a narrower dark band. Body and limbs dark (dark brown, dusky-brown or dark bluish-grey), either uniform (cT cT), or with whitish or bluish dots (9 9); tail uniformly dark brown. Ventrally, head bluish-white, bluish-grey or tan, with or without dark spots (fewer than dorsally); body, limbs and tail from as dark as, to distinctly lighter than dorsally; in MPEG 15988, underside of tail reddish.
In UIMNH 79943, UIMNH 91712 (
CommentUracentron has been redefined as synonym of Tropidurus by Frost (1992) and revalidated by FROST et al. (2001). Synonymy partly after Peters et al. 1970. Illustrations in Lamar (1997).

Probably also in Bolivia but not found yet (fide LANGSTROTH 2005) 
EtymologyNamed after Latin flavus = yellow and “ceps” = head, although the head may be greenish or yellowish. 
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