These researchers found two mtDNA haplotypes within the taxon Ateles fusciceps, which they argued could indicate the existence of two distinct evolutionary lineages and possibly two subspecies: A.f. rufiventris and A. f. robustus. Also, due to the detection of common microsatellite alleles (unpublished data) between northern populations of A. fusciceps and A. hybridus, they suggested that some degree of gene flow might occur between these two putative species (Ruiz-Garcia and Alvarez, 2003).