The Taxonomy of Howler Monkeys: Integrating Old and New Knowledge from Morphological and Genetic Studies

Abstract

The taxonomic history of the howler monkeys, genus Alouatta, has been long, complex, and filled with omissions and mistakes. This has created confusion over the validity of different taxa. Here we review the taxonomic history of the genus and evaluate the validity of the different taxa based on current knowledge generated through morphological and genetic studies. We recognize nine species of howlers (A. palliata, A. pigra, A. seniculus, A. arctoidea, A. sara, A. macconnelli, A. guariba, A. belzebul, A. caraya) and three more taxa that we tentatively consider full species (A. nigerrima, A. ululata, A. discolor), but for which genetic and/or morphological studies are required to confirm this status. We recognize five subspecies in A. palliata (A. p. mexicana, A. p. palliata, A. p. coibensis, A. p. trabeata, and A. p. aequatorialis), three in A. seniculus, (A. s. seniculus, A. s. juara, and A. s. puruensis), two in A. guariba (A. g. guariba and A. g. clamitans), and acknowledge the possibility that A. pigra may have two subspecies (A. p. pigra and A. p. luctuosa). Most species and subspecies require field studies to determine their actual distribution ranges. Furthermore, a combination of morphological and genetic analyses is needed to confirm the validity of several taxa. Given the broad presence of howler monkeys in the Neotropics, these studies would require the collaboration of a multidisciplinary network of researchers across the range of distribution of the genus.