Anthony B. Rylands. Deputy Chair, IUCN SSC Primate Specialist Group, Office of the President, Conservation International , 2011 Crystal Drive, Arlington, Virginia 22202, USA
Colin P. Groves. Department of Archaeology and Anthropology, The Australian National University, GPO Box 4, Canberra ACT 0200, Australia
Wilson, Don E., and DeeAnn M. Reeder, eds. 1992-01-01. Mammal Species of the World: A Taxonomic and Geographic Reference, 2nd ed., 3rd printing. Smithsonian Institution Press. Washington, DC, USA. xviii + 1207. 1-56098-217-9. Corrections were made to text at 3rd printing.
Wilson, Don E., and DeeAnn M. Reeder, eds. 2005-10-01. Mammal Species of the World: A Taxonomic and Geographic Reference, 3rd ed., vol. 1. Johns Hopkins University Press. Baltimore, Maryland, USA. xxxv + 743. 0-8018-8221-4. .
Wilson, Don E., and F. Russell Cole 2000-01-01. Common Names of Mammals of the World. Smithsonian Institution Press. Washington, DC, USA. xiv + 204. 1-56098-383-3. With contributions by Bernadette N. Graham, Adam P. Potter, and Mariana M. Upmeyer.
Mittermeier, Rusell A., Anthony B. Rylands, and Don E. Wilson, eds. 2013-01-01. Handbook of the Mammals of the World. Volume 3. Primates. Lynx Edicions. Barcelona, Spain. 951. 9788496553897. .
Wilson & Reeder, eds. (2005): Comments: Groves (1989:87) suggested that H. g. alaotrensis may be a full species, and both alaotrensis and occidentalis were definitively separated as species by Groves (2001c)
Wilson & Reeder, eds. (2005): Status: CITES - Appendix I; U.S. ESA - Endangered; IUCN - Lower Risk (nt) as H. g. griseus, otherwise Lower Risk (lc)