Since the late 1800s, experts have thought that the long-necked dinosaurs known as sauropods were herbivores. Given the flat shape of their small teeth and the giant size of their bodies—which were not equipped to chase around prey and would have required them to eat often—researchers assumed sauropods browsed from trees and other greenery.

It’s the smoking gun, or the steaming guts,” said a paleontologist from a team that also found that the sauropods didn’t chew their food.

Plant fossils found in the abdomen of a sauropod support the long-standing hypothesis that these dinosaurs were herbivores, finds a study publishing June 9 in the Cell Press journal Current Biology. T