New study traces the evolutionary history of what mammals eat. National Evolutionary Synthesis Center, April 16, 2012. The feeding habits of mammals haven’t always been what they are today, particularly for omnivores, finds a new study. Some groups of mammals almost exclusively eat meat — take lions and tigers and other big cats. Other mammals such as deer, cows and antelope are predominantly plant-eaters, living on a diet of leaves, shoots and bark. But particularly for omnivores, the situation wasn’t always that way, researchers report. Picked up by NSF and NPR.