SCIENCE

Tyrannosaurus Scat

Science Correspondent

March 9, 2011

Tyrannosaurus ate flesh. That much is obvious. The reinforced skull and huge, serrated teeth of the tyrant dinosaur and its kin were not adaptations for cropping grass or cracking coconuts. Both predators and scavengers, the tyrannosaurs must have consumed massive amounts of meat to fuel their large bodies, and paleontologists have been fortunate enough to find a few traces of tyrannosaur meals.

Feeding traces are rare in the fossil record. The very act of feeding itself at least partially destroys the organisms being fed upon—see this time-lapse video of an African elephant carcass to see how efficiently a group of carnivores can dismantle a body—and it takes a series of exceptional circumstances for bite-marks to be preserved. In the case of tyrannosaurs, paleontologists have found distinctive bite marks on Triceratops, hadrosaurs, and even other tyrannosaurs, but there is another category of trace fossils that can tell us something about dinosaur diets: gut contents and scat.

In 1998, paleontologists Karen Chin, Timothy Tokaryk, Gregory Erickson and Lewis Calk described the enormous droppings of a theropod dinosaur found in southwestern Saskatchewan, Canada. Technically termed a coprolite, the foot-and-a-half-long mass of fossil feces was left by a large dinosaur a little more than 65.5 million years ago, and two factors confirmed that it had been left by a carnivorous dinosaur. Not only did the coprolite have elevated levels of phosphorous phosphorus—a common chemical feature of carnivore scat—but about thirty-to-fifty percent of the mass was broken fragments of bone from a young dinosaur. The only dinosaur found in the area capable of leaving behind this trace fossil was Tyrannosaurus rex, and the authors of the report concluded "this rare example of fossilized dietary residues helps to refine our understanding of theropod feeding behaviour by providing physical evidence that a tyrannosaur crushed, consumed, and incompletely digested large quantities of bone when feeding on a subadult dinosaur."

Chin and a different team of researchers reported a second tyrannosaur coprolite in 2003. The highly fractured fossil was found in the approximately 75-million-year-old rock of Alberta's Dinosaur Park Formation—home to the tyrannosaurs Daspletosaurus and Gorgosaurus—and careful study of the coprolite's contents revealed small bits of fossilized soft tissue that had not been fully digested. The large amount of bone in the Saskatchewan coprolite and the numerous traces of soft tissue in the Alberta coprolite suggested that the food tyrannosaurs ingested did not remain in their digestive systems long enough for all of it to break down, making their digestive systems unlike those of living crocodiles and snakes. Tyrannosaurs consumed large amounts of flesh and bone, but it passed through their systems relatively rapidly.

Paleontologists may have even found gut contents still inside the body of a tyrannosaur. In 2001, paleontologist David Varricchio described a partial Daspletosaurus skeleton from western Montana's Two Medicine Formation, and near the partial hips of the predator were parts of the tail and jaw of a juvenile hadrosaur. The young hadrosaur bones appeared to be degraded by acid—they had a spongy and pitted appearance different from typical bone—and the Daspletosaurus body was found near a low-energy, seasonal pond, making it unlikely that the body of a young hadrosaur had been washed in and mixed up with the predator. Citing his find and the coprolite announced by Chin and co-authors in 1998, Varricchio proposed that juvenile and sub-adult dinosaurs may have been common prey for tyrannosaurs, an idea supported by scientists David Hone and Oliver Rauhut in their 2009 review of predatory dinosaur feeding habits. For large predators like tyrannosaurs, juvenile dinosaurs may have been easing pickings.

Frustratingly, the sample size of tyrannosaur coprolites and gut contents is very small. More of these trace fossils will be needed to further investigate what these dinosaurs were regularly eating and how they might have digested their food. Even so, each coprolite is like a time capsule that can tell us something about an animal's diet and biology—behavior, diet, physiology, and internal anatomy, all wrapped up in a bit of tyrannosaur scat.

References:

CHIN, K., EBERTH, D., SCHWEITZER, M., RANDO, T., SLOBODA, W., & HORNER, J. (2003). Remarkable Preservation of Undigested Muscle Tissue Within a Late Cretaceous Tyrannosaurid Coprolite from Alberta, Canada PALAIOS, 18 (3), 286-294 DOI: 10.1669/0883-1351(2003)0182.0.CO;2

Chin, K., Tokaryk, T., Erickson, G., & Calk, L. (1998). A king-sized theropod coprolite Nature, 393 (6686), 680-682 DOI: 10.1038/31461

Erickson, G., & Olson, K. (1996). Bite marks attributable to Tyrannosaurus rex: Preliminary description and implications Journal of Vertebrate Paleontology, 16 (1), 175-178 DOI: 10.1080/02724634.1996.10011297

VARRICCHIO, D. (2001). GUT CONTENTS FROM A CRETACEOUS TYRANNOSAURID: IMPLICATIONS FOR THEROPOD DINOSAUR DIGESTIVE TRACTS Journal of Paleontology, 75 (2), 401-406 DOI: 10.1666/0022-3360(2001)0752.0.CO;2