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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 dinosaurs1,2,3, 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

Belgium4 and India5,6 that have been attributed to dinosaurs might have been produced by contemporaneous crocodylians7 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.

We thank W. Sloboda for the discovery of the coprolite; the Allemand family for permitting access to the land and its fossils; H. N. Bryant, M. J. Jurashius, C. E. Meyer, M. Moreno, R. L.

Oscarson, J. F. Parham, D. Pierce, J. Rifkin and B. H. Tiffney for comments and technical assistance; the Royal Saskatchewan Museum, Stanford University, the US Geological Survey, and the

University of California at Santa Barbara for technical and administrative assistance; and the late W. V. Sliter for support and encouragement.

Present address: Biomechanical Engineering Division, Mechanical Engineering Department,

United States Geological Survey, 345 Middlefield Road, MS 975, Menlo Park, 94025, California, USA

Eastend Fossil Research Station, Royal Saskatchewan Museum, Box 460, Eastend, S0N 0T0, Saskatchewan, Canada

Department of Integrative Biology & Museums of Vertebrate Zoology and Paleontology, University of California, Berkeley, 94720, California, USA

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