A Scatological Dinosaur Surprise

Karen Chin, a paleontologist at the University of Colorado at Boulder, was befuddled when she found chunks of undigested meat in a 75-million-year-old hunk of fossilized dinosaur dung from an ancestor of Tyrannosaurus rex. “It took me a while to convince myself that this was really muscle tissue,” she says. Soft animal tissue rarely survives the digestive tract, much less the fossilization process. Paleontologist Jack Horner of Montana State University examined bone fragments in the fossil dung—called a coprolite—and tentatively identified them as the remains of a thick-headed plant-eating dinosaur called a pachycephalosaur. This identification makes the preserved muscle only the fifth example of fossilized dinosaur flesh ever found and the first ever in a coprolite. The ancient feces open up a new way to investigate whether dinosaurs were active, warm-blooded creatures. Cold-blooded meat eaters tend to digest their meals slowly, whereas food passes through modern warm-blooded carnivores quickly, often leaving undigested bits in their dung. Cells in the bits of tissue in the fossilized dung might offer additional clues. The preserved muscle fibers may contain telling structures or molecular signatures that could help identify dinosaurs as warm-blooded, cold-blooded, or something in between, as some researchers suspect. More information may be coming soon: Now that she knows to look, Chin has already found muscle fibers in a couple of other coprolites.