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Probable Gut Contents Within A Specimen Of Brachylophosaurus Canadensis (Dinosauria: Hadrosauridae) From the Upper Cretaceous Judith River Formation Of Montana

¹ Department of Geological Sciences, University of Colorado at Boulder, Boulder, Colorado 80309, USA
² Geological Sciences/Museum of Natural History, UCB 265, University of Colorado at Boulder, Boulder, Colorado 80309, USA
³ Royal Tyrrell Museum of Palaeontology, Box 7500, Drumheller, Alberta, T0J 0Y0, Canada
⁴ Express Distributing, 2508 Overland Ave., Billings, Montana 59102, USA tweet{at}colorado.edu

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 cm³, and comparable material is not found outside the carcass. The carcass contents include 63% clay, 16% undetermined matrix, 12% organic matter, and 9% larger inorganic clasts—mostly 50–100 µm 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.

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