It is important to point out that because of the lack of recombination in the mitochondrial genome, our results constitute a phylogenetic hypothesis based on a single gene tree. While gene trees are an important tool in molecular systematics, and while we expect gene trees to often match the species tree (Avise, 2004), it is not uncommon for phylogenetic analyses of different gene trees to yield different inferences of the phylogenetic relationships among a group of organisms. Reconstruction of the evolutionary relationships among spider monkey taxa would be improved by inclusion of DNA sequence data from multiple unlinked nuclear loci.