The Systematic Status of the Black Howler Monkey, Alouatta Pigra Lawrence

Abstract

An apparent case of sympatry between two supposed races of Alouatta pallida (Gray) was discovered near Macuspana, Tabasco, Mexico. Howler monkeys in the Tabascan series were easily separated into two distinct groups based on various characteristics of the cranium, dentition, and pelage. Further comparisons revealed that these two groups were identifiable as Alouatta palliata mexicana Merriam and Alouatta palliata pigra Lawrence. Several possible interpretations of this situation are discussed and, in view of the observed sympatry and distinctive morphological differences, pigra is elevated to specific status; the systematic status of Ahuatta villosa (Gray) also is discussed. Several admittedly speculative explanations are offered to account for the existence of two distinct species of howler monkeys in Middle America.