Fossil faeces (coprolites) provide unique trophic perspectives on ancient ecosystems. Yet, although thousands of coprolites have been discovered, specimens that can be unequivocally attributed to carnivorous dinosaurs are almost unknown. A few fossil faeces have been ascribed to herbivorous dinosaurs 1-3 , but it is more difficult to identify coprolites produced by theropods because other carnivorous taxa coexisted with dinosaurs and most faeces are taxonomically ambiguous. Thus sizeable (up to 20 cm long and 10 cm wide) phosphatic coprolites from Belgium 4 and India 5,6 that have been attributed to dinosaurs might have been produced by contemporaneous crocodylians 7 or fish. But there is no ambiguity about the theropod origin of the Cretaceous coprolite we report here. This specimen is more than twice as large as any previously reported carnivore coprolite, and its great size and temporal and geographic context indicate that it was produced by a tyrannosaur, most likely Tyrannosaurus rex. The specimen contains a high proportion (30-50%) of bone fragments, and is rare tangible evidence of theropod diet and digestive processes.The specimen (SMNH P2609.1) was discovered as an elongate mass weathering out of the fluvial Maastrichtian Frenchman Formation in Southwestern Saskatchewan, roughly 35 km southeast of the town of Eastend. The fractured mass was distinguished by its indurated nature and numerous inclusions of comminuted bone. The main portion of the mass was found in situ in a bentonitic mudstone, though numerous fragments had eroded downslope. No fossil bones were found in association with the coprolite, but fossils of a number of large vertebrates have been recovered from the Frenchman Formation 8 .The main body of the specimen is roughly 44 cm long, 13 cm high and 16 cm wide (Fig. 1). The density of the material (approximately 2.94 g ml −1 ) and the weight of all portions (over 7.1 kg) indicate that the present volume of the mass is ϳ2.4 litres, though it is likely that the original faecal mass was larger before it was subjected to compaction, attrition, and/or desiccation. Broken surfaces of the specimen expose numerous dark brown macroscopic bone fragments ranging from 2 to 34 mm in length. These pieces are suspended in a microcrystalline ground mass and are generally aligned in a consistent direction. The ground mass also contains sand-sized bone clasts (Fig. 2). Most of the included bone appears to be similar in type, with highly vascularized cortical bone tissue up to 14-mm thick in a fibrolamellar pattern. All of the observed bone is primary, and no lines of arrested growth were detected.Bulk chemical analyses using X-ray fluorescence (Table 1) reveal marked differences between the specimen and the Frenchman Formation mudstone. The bone-bearing specimen contains high concentrations of phosphorus and calcium, and lower concentrations of aluminium and silicon, relative to the host sediment. Microprobe analyses of specific areas of the specimen indicate that the bone fragments and coprolitic ground mass...

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Exceptionally detailed soft tissues have been identified within the fossilized feces of a large Cretaceous tyrannosaurid. Microscopic cord-like structures in the coprolitic ground mass are visible in thin section and with scanning electron microscopy. The morphology, organization, and context of these structures indicate that they are the fossilized remains of undigested muscle tissue. This unusual discovery indicates specific digestive and taphonomic conditions, including a relatively short gut-residence time, rapid lithification, and minimal diagenetic recrystallization. Rapid burial of the feces probably was facilitated by a flood event on the ancient coastal lowland plain on which the fecal mass was deposited.

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 ϳ63% clay, ϳ16% undetermined matrix, ϳ12% organic matter, and ϳ9% larger inorganic clasts-mostly 50-100 m 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.