Accepted by M. Vences: 9 Sep. 2011; published: 29 Sep. 2011 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2011 · Magnolia Press Zootaxa 3045: 57–67 (2011) www.mapress.com/ zootaxa/ Article 57 A new species of harlequin frog (Bufonidae: Atelopus) with an unusual behavior from Andes of Colombia LAURA BRAVO-VALENCIA 1 & MAURICIO RIVERA-CORREA 1,2,3 1 Grupo Herpetológico de Antioquia, Instituto de Biología, Universidad de Antioquia, Calle 67 # 53–108, Bloque 7–121, Medellín, Colombia, A.A. 1226 2 Programa de Pós-Graduação em Zoologia, Faculdade de Biociências, Pontifícia Universidade Católica do Rio Grande do Sul, Av. Ipiranga 6681, 90619-900, Porto Alegre, RS, Brasil. E-mail: mauriciorivera79@yahoo.com.ar 3 Corresponding author. E-mail: mauriciorivera79@yahoo.com.ar Abstract A new species of harlequin frog, genus Atelopus, is described from the highlands in the northern part of the Cordillera Central, Colombia. The new species, is distinguished from all other species in the genus by the presence of a postorbital crest widely raised, well defined coni in postocular region and arms, small warts and spiculae scattered on the dorsal sur- faces of the body and thighs and, vertebral neural processes conspicuous. Females are uniform dark reddish brown on dor- sum, and bright orange ventrally; males are dark brown dorsally, and ventrally white or yellowish with dark brown irregular stripes and blotches. The conservation population status of the new species is discussed, additionally the natural history and aspects about an unusual behavior in the genus is provided. Key words: Atelopus nocturnus sp. nov., Cordillera Central, Colombia, natural history, taxonomy Resumen Describimos una nueva especie de rana arlequín del género Atelopus de tierras altas en el norte de la Cordillera Central de los Andes de Colombia. La nueva especie se distingue de las otras especies del género por la presencia de una cresta postorbital ampliamente levantada, coni en la región posterior al ojo y en los brazos, pequeñas verrugas y tubérculos en la superficie dorsal del cuerpo y muslos, y proceso vertebral neural visible. Las hembras son café rojizo uniforme en el dorso y naranja brillante en el vientre; en machos el dorso es caf oscuro y vientre blanco o crema amarillento con manchas irregulares café oscuro. Discutimos el estatus de conservación de la nueva especie, además, proveemos aspectos de la his- toria natural y de un comportamiento inusual en el género. Palabras clave: Atelopus nocturnus sp. nov., Cordillera Central, Colombia, historia natural, taxonomía Introduction Although some species are found only in biological collections, the genus Atelopus still is one of the most diverse and conspicuous components of the neotropical anurofauna. This is the richest among the toads to family Bufoni- dae currently containing 94 described species (Frost 2011), has diurnal activity (Rueda et al. 2005, Lötters 2007, Coloma et al. 2002) and due to its bright color commonly referred to as harlequin frogs. Atelopus live at or in the margins of streams and running water is utilized for reproduction (Lötters 2007), and most species occur in moun- tain habitats above 1500 m (see Lötters 1996; IUCN 2010). Apparently due to association with the streams and the physiognomy of the Andes has resulted in restricted area of distribution of species (Ltters 1996; La Marca et al. 2005), and has promoted diversification in this genus. Throughout Central and South America, 97% of the species of the genus are regarded as Endangered, Critically Endangered or Extinct, according to IUCN Red List criteria (Stuart et al. 2008), because populations are known to have declined dramatically (e.g. Ron et al. 2003, La Marca