abstract 2009 Elsevier Inc. All rights reserved. 1. IntroductionThe nocturnal owl monkeys, Aotus spp. (Infraorder Platyrrhini),are distributed in the Neotropics from southern Panama to North-ern Argentina (Fig. 1), although they are absent from Brazil’s Atlan-tic Forest (Hershkovitz, 1983). Despite its relative lack ofmorphological variation in comparison with other platyrrhine gen-era, Aotus has proven to be one of the most difficult to interpret inphylogenetic terms. There is still no clear consensus on the posi-tion of the genus within the Platyrrhini (e.g., Kay, 1990; Schneideret al., 2001; Steiper and Ruvolo, 2003; Rosenberger and Tejedor, inpress), and there is at least as much controversy over the numberof owl monkey species.Aotus was originally considered to be a monotypic genus with asingle species, Aotus trivirgatus (Hershkovitz, 1949). However,Brumback et al. (1971) identified considerable karyotypic varia-tion, which led to the proposal of a number of new species (Brum-back, 1974; Thorington and Vorek, 1976). At least 18 distinctkaryotypes are now known, with 2n varying between 46 and 58(Ma et al., 1976, 1985; Galbreath, 1983; Pieczarka et al., 1993; Tor-res et al., 1998).Following these initial cytogenetic discoveries, Hershkovitz(1983) revised the genus based on genetic, morphometric, andzoogeographic parameters, and proposed a scheme encompass-ing nine species and four subspecies, arranged in two maingroups, based on the coloration of the pelage on the sides ofthe neck. The ‘‘gray-necked” group is distributed north of theAmazon, whereas the ‘‘red-necked” group occurs south of thisriver (Fig. 1).Hershkovitz’s (1983) scheme was challenged by subsequentstudies based on cytogenetics (e.g., Pieczarka et al., 1993; Defleret al., 2001), morphology (Ford, 1994; Defler et al., 2001), andmolecular data (Ashley and Vaughn, 1995). Ford (1994), for exam-ple, realigned the forms into just five species. In the first molecularstudy of the genus, Ashley and Vaughn (1995) used the nucleotidesequences of subunit II of the cytochrome c oxidase (COII) enzymefrom three of Hershkovitz’s taxa (Aotus lemurinus griseimembra, Ao-tus nancymai, and Aotus azarae boliviensis), and observed highlydivergent values, with a phylogenetic tree which contradictedthe gray/red-neck dichotomy.As all present-day platyrrhines are the result of a quite re-cent, Early Miocene diversification (Goodman et al., 1998;Schneider et al., 2001; Steiper and Ruvolo, 2003; Opazo et al.,2006; Poux et al., 2006), COII gene sequences have proven usefulfor the interpretation of both intra- and intergeneric relation-ships (Figueiredo et al., 1998; Collins and Dubach, 2000a, b; Asc-unce et al., 2002; Sena et al., 2002; Nieves et al., 2005). In thepresent study, the phylogenetic relationships among seven ofHershkovitz’s (1983) Aotus taxa were evaluated using COII genesequences, constituting a more robust sample than Ashley andVaughn (1995) study.