primate species such as spider monkeys are likely to be some of the first species to be extirpated. Reintroduction efforts by researchers at Reserva Ecologica Taricaya have begun along the lower Madre de Dios river where conservation efforts now provide a suitable release site and protected habitat. Similar or related species In addition to external appearance, the Peruvian spider monkey differs from the red-faced spider monkey by the number of chromosomes (2n = 32 in the red-faced vs. 2n = 34 in the Peruvian) in addition to several specific chromosomal differences. The two species have been interbred in captivity, resulting in offspring with reduced fertility (but not sterility). There are several related species such as the Central American spider monkey or Geoffroy's spider monkey (A. geoffroyi), and the brown spider monkey (A. hybridus) and the species' closest relative the white-bellied spider monkey (A. belzebuth). All of these have a prehensile tail, a thumbless hand, and other characteristics that are found in all spider monkeys. References Spider monkeys Mammals of Brazil Mammals of Peru Mammals of Bolivia Mammals described in 1812 Primates of South America Taxa named by Alexander von Humboldt