On a summer day 110 million years ago, an armored dinosaur likely ambled through the remains of a wildfire in what is now Alberta, Canada, gobbling up delicate green ferns peeking out from the ash. Somehow, shortly after, the dinosaur ended up dead in a river among the Cretaceous landscape and was swept out to sea. The ancient creature remained entombed in marine sediments until 2011, when an oil-sands miner stumbled across the remains: the best-preserved dinosaur of its kind ever discovered.

Already, the fossil has shed new light on how armored dinosaurs’ hardened exteriors looked and functioned. Now, scientists studying the extraordinary fossil have made a new discovery: a ball of plant matter in the dinosaur’s gut that