Published August 9, 2023. Updated January 29, 2024. Open access.

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Amazon Thornytail-Iguana (Uracentron flaviceps)

Reptiles of Ecuador | Sauria | Tropiduridae | Uracentron flaviceps

English common names: Amazon Thornytail Iguana, Tropical Thornytail Iguana.

Spanish common name: Trepatroncos espinoso.

Recognition: ♂♂ 19.2 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=13.0 cm. ♀♀ 13.1 cmMaximum distance from the snout to the tip of the tail. Snout–vent length=9.6 cm..13 The Amazon Thornytail Iguana (Uracentron flaviceps) is unmistakable among lizards in the Ecuadorian Amazon by having a flat leaf-like tail with whorls of spinose scales.1 The dorsal scales are small, imbricate, and strongly keeled.1 The coloration is also unmistakable. Dominant adult males are almost entirely blackish with minute yellowish or orangish spots, a pale yellow nuchal band (present depending on the population), and a broad orange head with black spots.14 Females and juveniles have a greenish head, collar, and abundant green or cream pigment on the anterior half of the body (Fig. 1).1,2 The only similar Ecuadorian lizard in shape and coloration is Plica plica, but the tail in this reptile is long and thin.24

Figure showing variation among individuals of Uracentron flaviceps

Figure 1: Individuals of Uracentron flaviceps from Ecuador: Cuyabeno Reserve, Sucumbíos province (); Yasuní National Park, Orellana province (). j=juvenile.

Natural history: Uracentron flaviceps is a strictly arboreal lizard that inhabits lowland seasonally-flooded forests and terra-firme forests.35 Though locally frequent, these lizards can be extremely difficult to observe given their occurrence in the upper rainforest strata, up to 40 m above the ground.6 Amazon Thornytail Iguanas are gregarious. They live in groups of 2–16 individuals in a single tree: one sexually mature adult male and one or more adult females and many juveniles.3,5 Additional adult males may be found in the same tree, but these have small testes and a subdued coloration.3 This species usually lives on the tallest trees and many individuals occupy the same hole as a nocturnal retreat.3,5 These iguanas are diurnal and can be active whenever the sun is out, but not during overcast days.3,7 The dominant males are usually the first to go out, an action that is followed by their survey of the territory. Active individuals of all age categories follow shortly and can be seen foraging and basking along the trunks and branches throughout the day. The diet of U. flaviceps is composed almost entirely on ants,7 but can also include beetles, flies, grasshoppers, and centipedes.2,4 When disturbed, individuals usually run across the trunks and disappear into tree holes.3 In flooded forests, they can also disappear below the water surface along the trunk, remaining up to three minutes submerged.6 Males defend their territories from non-resident males using visual displays. Females lay clutches of two eggs2 in communal nesting sites where 5–14 eggs may be found simoultaneously.26 Breeding seems to take place year around and the reproductive system is polygyny, with one male monopolizing access to all females.2,3,7

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Conservation: Least Concern Believed to be safe from extinction given current circumstances..8 Uracentron flaviceps is listed in this category given its wide distribution, presumed stable populations, and presence in protected areas.8 Therefore, the species is considered to be facing no major immediate threats of extinction.8 However, since U. flaviceps is a strictly arboreal lizard, some populations are undoubtedly destined to disappear due to large-scale deforestation caused by the expansion of the agricultural frontier.

Distribution: Uracentron flaviceps is native to the upper Amazon basin of Brazil, Colombia, Ecuador (Fig. 2), and Peru.9

Distribution of Uracentron flaviceps in Ecuador

Figure 2: Distribution of Uracentron flaviceps in Ecuador. See Appendix 1 for a complete list of the presence localities included in the map.

Etymology: The generic name Uracentron comes from the Greek oura (=tail) and kentron (=spike),10 and refers to the unique tail architecture of this lizard. The specific epithet flaviceps is derived from the Latin words flavus (=yellow) and ceps (=head),10 and refers to the male coloration.

See it in the wild: Amazon Thornytail Iguanas can be seen almost every day on the emerging tree at the observation tower of Napo Wildlife Center. They are also comparatively common along the borders of Laguna Grande in Cuyabeno Reserve.

Special thanks to Suzana Lightman for symbolically adopting the Amazon Thornytail Iguana and helping bring the Reptiles of Ecuador book project to life.

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Author: Alejandro ArteagaaAffiliation: Khamai Foundation, Quito, Ecuador.

Photographer: Jose VieirabAffiliation: Tropical Herping (TH), Quito, Ecuador.,cAffiliation: ExSitu, Quito, Ecuador.

How to cite? Arteaga A (2024) Amazon Thornytail-Iguana (Uracentron flaviceps). In: Arteaga A, Bustamante L, Vieira J (Eds) Reptiles of Ecuador: Life in the middle of the world. Available from: DOI: 10.47051/QUKP3916

Literature cited:

  1. Etheridge R (1968) A review of the iguanid lizard genera Uracentron and Strobilurus. Bulletin of the British Museum (Natural History) 17: 47–64.
  2. Avila-Pires TCS (1995) Lizards of Brazilian Amazonia (Reptilia: Squamata). Zoologische Verhandelingen 299: 1–706.
  3. Vitt LJ, De la Torre S (1996) A research guide to the lizards of Cuyabeno. Pontificia Universidad Católica del Ecuador, Quito, 165 pp.
  4. Duellman WE (1978) The biology of an equatorial herpetofauna in Amazonian Ecuador. Publications of the Museum of Natural History, University of Kansas 65: 1–352.
  5. Dixon JR, Soini P (1986) The reptiles of the upper Amazon Basin, Iquitos region, Peru. Milwaukee Public Museum, Milwaukee, 154 pp.
  6. Field notes, Reptiles of Ecuador book project.
  7. Vitt LJ, Zani PA (1996) Ecology of the elusive tropical lizard Tropidurus [=Uracentron] flaviceps (Tropiduridae) in lowland rain forest of Ecuador. Herpetologica 52: 121–132.
  8. Avila-Pires TCS, Aparicio J, Moravec J, Perez P, Daza J, Cisneros-Heredia DF (2019) Uracentron flaviceps. The IUCN Red List of threatened species. Available from: DOI: 10.2305/IUCN.UK.2019-2.RLTS.T44579982A44579991.en
  9. Ribeiro-Júnior MA (2015) Catalogue of distribution of lizards (Reptilia: Squamata) from the Brazilian Amazonia. I. Dactyloidae, Hoplocercidae, Iguanidae, Leiosauridae, Polychrotidae, Tropiduridae. Zootaxa 3983: 001–110. DOI: 10.11646/zootaxa.3983.1.1
  10. Brown RW (1956) Composition of scientific words. Smithsonian Books, Washington D.C., 882 pp.

Appendix 1: Locality data used to create the distribution map of Uracentron flaviceps in Ecuador (Fig. 2). Go to the section on symbols and abbreviations for a list of acronyms used.

ColombiaCaquetáFlorenciaiNaturalist; photo examined
ColombiaCaquetáSan José del FraguaiNaturalist; photo examined
ColombiaPutumayoPuerto LeguízamoICN 2228; Calderón et al. 2023
ColombiaPutumayoRío GuamuésEtheridge 1968
ColombiaPutumayoRío PutumayoGrant et al. 2023
EcuadorMorona SantiagoMacumaiNaturalist; photo examined
EcuadorNapoAhuanoPhoto by Diego Piñán
EcuadorNapoJatun Sacha Biological ReserveVigle 2008
EcuadorOrellanaBloque 43, Campo ITTPhoto by María José Quiroz
EcuadorOrellanaComunidad AñanguiNaturalist; photo examined
EcuadorOrellanaEl CocaRibeiro-Júnior 2015
EcuadorOrellanaKawymenoiNaturalist; photo examined
EcuadorOrellanaNapo Wildlife CenterThis work; Fig. 1
EcuadorOrellanaSan José de PayaminoMaynard et al. 2017
EcuadorOrellanaTiputini Biodiversity Station Cisneros-Heredia 2003
EcuadorPastazaBalsauraOrtega-Andrade 2010
EcuadorPastazaCabeceras del BobonazaRibeiro-Júnior 2015
EcuadorPastazaCachiyacuOrtega-Andrade 2010
EcuadorPastazaCanelosEtheridge 1968
EcuadorPastazaChichirotaCAS 16100; VertNet
EcuadorPastazaJuyuintzaOrtega-Andrade 2010
EcuadorPastazaRío Copataza, mouth ofAvila-Pires 1995
EcuadorPastazaRío LipunoRibeiro-Júnior 2015
EcuadorPastazaRío Pastaza Etheridge 1968
EcuadorPastazaRío PindoUSNM 201390; VertNet
EcuadorPastazaRío VillanoiNaturalist; photo examined
EcuadorPastazaSarayacuEtheridge 1968
EcuadorPastazaTeneveraPhoto by Dillon Anderson
EcuadorSucumbíosCaiman LodgeiNaturalist; photo examined
EcuadorSucumbíosComunidad ZábaloCevallos Bustos 2010
EcuadorSucumbíosCuyabenoReptiles of Ecuador book
EcuadorSucumbíosCuyabeno ReserveiNaturalist; photo examined
EcuadorSucumbíosLago AgrioDuellman 1978
EcuadorSucumbíosLimoncocha Biological ReserveAvila-Pires 1995
EcuadorSucumbíosRío AguaricoiNaturalist; photo examined
EcuadorSucumbíosSanta Cecilia Etheridge 1968
EcuadorSucumbíosSanta ElenaiNaturalist; photo examined
EcuadorSucumbíosTarapoaRibeiro-Júnior 2015
PeruAmazonasHuampamiMVZ 163072; VertNet
PeruAmazonasRío CaterpizaMVZ 174844; VertNet
PeruLoretoBetween Apaga and NievaEtheridge 1968
PeruLoretoMisión de SarayacuAvila-Pires 1995
PeruLoretoMoroponTCWC 44573; VertNet
PeruLoretoPongo de MasericheEtheridge 1968
PeruLoretoRío YubinetoTapia del Águila et al. 2020
PeruLoretoYarina CochaEtheridge 1968