muiriquis 3.59 million years ago. Older studies by Porter, et al. indicate the howler monkeys are believed to have branched off from the other Atelides over 10 million years ago. In 2005 mammalian taxonomy reference work, Mammal Species of the World, listed five subspecies: Nicaraguan spider monkey, Ateles geoffroyi geoffroyi Hooded spider monkey, A. g. grisescens Ornate spider monkey, A. g. ornatus Mexican spider monkey, A. g. vellerosus Yucatan spider monkey, A. g. yucatanensis In 2015 a phylogenetic study recommended A. g. yucatanensis was a junior synonym of A. g. vellerosus. Some authorities also recognize A. g. azuerensis and A. g. frontatus as valid subspecies. The black-headed spider monkey, Ateles fusciceps, is considered by authorities such as Groves (1989) and Rylands et al. (2006) to be a separate species from Geoffroy's spider monkey. Other authorities, including Froelich (1991), Collins and Dubach (2001) and Nieves (2005), consider A. fusciceps to be synonymous with A. geoffroyi. Under this treatment, the two subspecies of the black-headed spider monkey represent additional subspecies of Geoffroy's spider monkey, A. g. fusciceps and A. g. rufiventris. Distribution and habitat The range of this species extends over much of Central America, encompassing Panama, Costa Rica, Nicaragua, Guatemala, Honduras, El Salvador, Belize and the south and much of the eastern portion of Mexico. Observations by local people indicate the southernmost subspecies, the hooded spider monkey, A. g. grisescens, may also occur in the portion of Colombia near the Panama border. In western Colombia and northeast Panama, it is replaced by the black-headed spider monkey, A. fusciceps, which is considered by some primatologists to be a subspecies of Geoffroy's spider monkey. Geoffroy's spider monkey lives in various types of forest, including rainforest, semideciduous and mangrove forests. Higher densities of Geoffroy's spider monkeys are generally found in areas containing evergreen forest. Physical description Geoffroy's spider monkey is one of the largest New World monkeys. Its length measures between and it weighs between . The tail is longer than the body at between . Males and females are approximately the same size. Its body color varies by subspecies and population, and can be buff, reddish, rust, brown or black. The hands and feet are dark or black. The face usually has a pale mask and bare skin around the eyes and muzzle. Its arms and legs are long and slim. The arms are about 25% longer than the legs. The thumb is