Probable gut contents within a specimen of Brachylophosaurus canadensis (Dinosauria : Hadrosauridae) from the Upper Cretaceous Judith River Formation of Montana

An exceptionally preserved subadult specimen (JRF 115H) of a hadrosaurid, Brachylophosaurus canadensis, from the Judith River Formation near Malta, Montana, contains abundant plant fragments concentrated within the body cavity. We examined the taphonomy of the carcass and analyzed the gut-region material to test whether the organic remains represent fossilized gut contents. The dinosaur was buried in a fluvial channel setting, and the excellent articulation, integument impressions, and lack of scavenging indicate rapid burial. The organic material occupies a volume of at least 5750 cm(3), and comparable material is not found outside the carcass. The carcass contents include similar to 63% clay, similar to 16% undetermined matrix, similar to 12% organic matter, and similar to 9% larger inorganic clasts-mostly 50-100 gin quartz grains. Most of the organics appear to be mm-scale leaf fragments. The most parsimonious explanation for the presence and composition of the gut-region material is that much of the plant fossils represent reworked brachylophosaur ingesta influenced by flowing water that entered through openings in the carcass and introduced clay. The evidence strongly suggests that the hadrosaurid ate significant quantities of leaves and processed them into small pieces. This study provides baseline information for analyzing other cases of putative gut contents in herbivorous dinosaurs.