A toothmark is an impression left by the bite of an animal with teeth, regardless of what was being bitten. Toothmarks are trace fossils, whereas the medium they bit into are body fossils. Dinosaur toothmarks, first described and interpreted in 1908 (Chapter 3), have been so far only reported from bones, and no dinosaur toothmarks in fossil plant material are currently known. For those dinosaurs that fed on other animals, some left distinctive toothmarks on bones, which clearly indicates their feeding habits. Whether these pieces of evidence are representative of feeding preferences for some dinosaurs is inconclusive and a firmer understanding depends on the discovery of more toothmarks or supplementary clues from stomach contents or coprolites. The behavioral significance of toothmarks is discussed at length in Chapter 14, where they will be explained to identify what dinosaurs ate.
Toothmarks have been attributed to specific dinosaurs on the basis of their close resemblance to known tooth anatomy (especially denticles on serrations) and spacing. Some reported examples from the Late Cretaceous include Troodon toothmarks in ceratopsian bones, Saurornitholestes toothmarks in bones of an ornithomimid and Edmontosaurus, and Tyrannosaurus toothmarks in neoceratopsian, hadrosaur, and Saurornitholestes bones. Of these examples, a direct correlation between "dinner" and "diner" species through toothmark evidence is of Tyrannosaurus toothmarks in Edmontosaurus and Triceratops bones (Chapters 9, 10, and 13). Similar toothmarks attributed to a closely-related species of tyrannosaurids, Albertosaurus, have also been interpreted from Edmontosaurus bones. This means that this species was a possibly popular choice on theropod menus, having been consumed by at least three species of them. However, such toothmarks do not necessarily mean that these theropods preyed upon and killed any of the eaten dinosaurs. After all, the specimens may have already been dead when they were munched. In contrast, tooth-marks from theropods that show post-wound healing have been reported for at least two specimens of the oft-victimized Edmontosaurus, which indicates a successful escape for a preyed-upon dinosaur, or a failed hunt for the predator.
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