In their early revision of the spid

In their early revision of the spider monkeys, pelage color was one of the most important characters used by Kellogg and Goldman (1944) to classify spider monkey species. While they found cranial features to be too variable both within and between species to give any reliable information that could be used to separate them, coloration, hair length, and other external features did seem to reliably separate geographically different forms into different species and subspecies. Since then, however, many other authors have noted that spider monkey pelage coloration can be highly variable (Collins and Dubach, 2000a; Froehlich et al., 1991; Hines, 2005). This variability is most striking in the Mesoamerican forms where overall body color can range from dark gray to red to light blond. South American spider monkeys, by contrast, are mostly black with variable facial marks, lighter colored crown patches, or a different, lighter ventral coloration. One exception to the black pattern among South American spider monkeys is Ateles hybridus, which is mostly brown with a cream-white belly and inner legs.