The simakobu (Simias concolor), or pig-tailed snubnosed langur, is one of four endemic primate species on the Mentawai Islands oV the west coast of Sumatra, Indonesia, and is currently considered a monotypic genus (BrandonJones et al., 2004; Miller, 1903). This species, like many other colobines, is a specialized folivore found in tropical rainforests. The simakobu monkey is a member of the “odd-nosed” group of Asian colobines, an informal grouping that also includes the proboscis monkey of Borneo (Nasalis larvatus), the snub-nosed monkeys of China and Vietnam (Rhinopithecus spp.), and the douc langurs of Vietnam, Laos, and Cambodia (Pygathrix spp.). There is no agreement, however, on the relationships among these genera, nor whether they even form a natural taxonomic or phylogenetic group (Delson, 1975; Groves, 1970, 2001; Jablonski, 1998; though see Sterner et al., in press). Geographically, the simakobu is found closest to the proboscis monkey, and some morphological data have indicated that these species are sister taxa. Both Simias and Nasalis exhibit narrow, long-faced skulls; long narrow nasal bones; and similar hair patterns (Groves, 1970). These two species appear to share more traits than do Rhinopithecus and Pygathrix, and some researchers have suggested that Simias should be subsumed into the genus Nasalis (Delson, 1975; Groves, 1970), perhaps as a subgenus (Delson, 1975); Groves (2001; Brandon-Jones, et al., 2004) appears to have retreated from the close linkage of these genera, though is not necessarily opposed to it (Groves, pers. comm.).