Kay, R. F. (1988). Oligocene. In I. Tattersal, E. Delson, & J. VanCouvering (Eds.), Encyclopedia of Human Evolution and Prehistory (pp. 392–394). New York: Garland Pub.

Kay, R. F. “Oligocene.” In Encyclopedia of Human Evolution and Prehistory, edited by I. Tattersal, E. Delson, and J. VanCouvering, 392–94. New York: Garland Pub., 1988.

Kay RF. Oligocene. In: Tattersal I, Delson E, VanCouvering J, editors. Encyclopedia of Human Evolution and Prehistory. New York: Garland Pub.; 1988. p. 392–4.

Kay, R. F. “Oligocene.” Encyclopedia of Human Evolution and Prehistory, edited by I. Tattersal et al., Garland Pub., 1988, pp. 392–94.

Kay RF. Oligocene. In: Tattersal I, Delson E, VanCouvering J, editors. Encyclopedia of Human Evolution and Prehistory. New York: Garland Pub.; 1988. p. 392–394.