Clues to fossil mammals' diets come from teeth, skull shape and the positions and strength of major jaw muscles, from fossilized dung and guts, from oxygen isotopes in bone and teeth, and from diets of similar modern animals.
Guthrie (1990)
Martin & Klein (1984)
(Owen (2002)
Therrien (2005)
Van Valkenburgh and Hertel (1993)