1. Ashton, E. H., 1954. Age changes in some bodily dimensions of apes.Proc. Zool. Soc. Lond., 124: 587–594.
2. Bourne, G. H., 1976. Pygmy chimpanzees at the Yerkes Center.Yerkes Newslet., 13(1): 2–7.
3. Coolidge, Jr., H. J., 1933.Pan paniscus: Pygmy chimpanzee from south of the Congo River.Amer. J. Phys. Anthropol. (old series), 18: 1–59.
4. Freckhop, S., 1935. A propos du chimpanzé de la rive gauche du Congo.Bull. Mus. Roy. Hist. Nat. Belge, 11: 1–43.
5. Gijzen, A., 1975. Studbook ofPan paniscus Schwarz, 1929.Acta Zool. Path., 61: 57–84.