Second, based on cytogenetic data, Medeiros et al. (1997) suggested that spider monkeys probably originated in the southwestern Amazon basin where populations of A. chamek currently are
found. From that area some populations would have migrated to the east to Brazil giving rise to A. marginatus, while others would have migrated to the northwest giving rise to A. belzebuth. The authors also proposed that Ateles hybridus, A. geoffroyi and A. fuscieps all originated from a single population, which migrated from the Amazon basin, possibly from ancestral populations of A.belzebuth. In Medeiros et al.’s (1997) study, Ateles paniscus was found to be the most derived species in terms of karyotype and possibly originated from the ancestral population of A. hybridus,after migrating eastwards along the north coast of South America.