Scientists have studied the feeding habits of the extinct Cave Bear. Based on the isotope composition in the collagen of the bears' bones, they were able to show that the large mammals subsisted on a purely vegan diet. The team proposes that it was this inflexible diet that led to the Cave Bear's extinction approximately 25,000 years ago.
https://www.sciencedaily.com/releases/2016/08/160823083557.htm