Cox, Barry, R.J. G. Savage, Brian Gardiner, and Colin Harrison. The Simon & Schuster Encylopedia of Dinosaurs & Prehistoric Creatures, Revised and Updated by Douglas Palmer. New York: Simon & Schuster, 1999.
Halstead, L.B. The Evolution of Mammals. Italy: Eurobook Limited, 1978
Ham, Ken and Bodie Hodge. The Answers Book for Kids Vol. 6. Arkansas: Master Books, 2013.
Answers Magazine 8, No. 2 (April–June 2013).
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