Psittacosaurus - Gastroliths in ribs

The closest living relatives to Psittacosaurus are birds and crocodiles, both of which have a gastric mill that requires small stones to be ingested to assist in processing their food. It should come as no surprise then, that the same was found in an adult Psittacosaurus. When the specimen was prepared in the prep lab, the preparators found a set of small polished stones inside the ribcage. When the Psittacosaurus died, the soft tissues that formed the gastric mill decayed, leaving the hard stones jumbled up in a loose pile inside the ribcage.