Gut contents from a Cretaceous Tyrannosaurid: Implications for theropod dinosaur digestive tracts

A partial skeleton of Daspletosaurus sp. from the Late Cretaceous (Campania n) Two Medicine Formation of western Montana preserves the first gut conten ts reported for a tyrannosaurid. Associated remains found with this skeleto n consist of acid-etched vertebrae and a fragmentary dentary from juvenile hadrosaur dinosaurs. Hadrosaur bonebed data and comparisons of hadrosaur an d tyrannosaurid limb proportions suggest that juvenile hadrosaurs represent ed both an abundant and accessible food source. The surface corrosion exhib ited by the hadrosaur elements matches that produced by stomach acids and d igestive enzymes in a wide variety of living vertebrates. Based upon these and other gut contents, and also upon tooth-marked bone studies, it appears that Daspletosaurus and most theropods ingested and digested prey in a man ner similar to that of extant archosaurs (crocodilians and birds), employin g a two-part stomach with an enzyme-producing proventriculus followed by a thick walled muscular gizzard. This two-part stomach appears to be an archo saur synapomorphy.