One of the most common herbivores of the dinosaur era might have been, well, not an herbivore. Fossilized poop likely to have come from a duck-billed dinosaur that roamed southern Utah some 75 million years ago contains ancient shellfish, shaking what researchers thought they knew about hadrosaurs and other egg-laying "herbivores." The feces also contained bits of wood. Whereas a single poop sample might suggest the crustaceans were accidentally ingested when the dinosaur snacked on a piece of rotting log, crustaceans found in 10 of 15 poop samples spread at different times across a 12-mile area indicate "a recurring diet," study author Karen Chin tells NPR. In fact, Chin believes the dinosaurs ate the wood only to get at the shellfish—possibly crayfish or crab, per Nature.
The crustaceans, which were at least 2 inches long, would have provided the extra protein necessary during the breeding season to produce healthy eggs. In other words, shell in, shell out. The rest of the time, the dinosaurs likely stuck to a typical herbivore diet, says Chin, noting other egg-laying "herbivores" like triceratops, stegosaurus, and brontosaurus might have done the same thing; modern bird species are also known to take in more protein and calcium during the breeding season, the researchers say in a release. Chin, whose research was published Thursday in Scientific Reports, notes the discovery of this "totally unexpected behavior" came as a big surprise, one that shows there's still "a lot we just don't know" about dinosaurs. (Dino eggs possibly came in a variety of colors.)