What did mammoths eat?
Mammoths were herbivores they ate plants. More specifically, they were grazers they ate grass.
How do we know?
We chew our food by moving our jaws up and down and side to side. Mammoths chewed their food differently. They chewed by putting grasses between their upper and lower molars, moving their lower jaw forward, dropping their jaw, moving it backward and repeating again sort of a grinding motion. This method of chewing works very well to grind grass. Try it. How do you think it would feel to chew this way?
Mastodon molar photo by Peter McLaughlin, Univ. of Delaware.