Physical evidence of predatory behavior in Tyrannosaurus rex

Abstract

Feeding strategies of the large theropod, Tyrannosaurus rex, either as a predator or a scavenger, have been a topic of debate previously compromised by lack of definitive physical evidence. Tooth drag and bone puncture marks have been documented on suggested prey items, but are often difficult to attribute to a specific theropod. Further, postmortem damage cannot be distinguished from intravital occurrences, unless evidence of healing is present. Here we report definitive evidence of predation by T. rex: a tooth crown embedded in a hadrosaurid caudal centrum, surrounded by healed bone growth. This indicates that the prey escaped and lived for some time after the injury, providing direct evidence of predatory behavior by T. rex. The two traumatically fused hadrosaur vertebrae partially enclosing a T. rex tooth were discovered in the Hell Creek Formation of South Dakota.

Fig. 1.

Depiction of a hadrosaur skeleton showing the position in the tail of the fused vertebrae (A) and a lateral view of the affected vertebrae with the circle indicating the location of the theropod tooth (B).

Fig. 2.

CT scans of the fused hadrosaur vertebrae, showing embedded theropod tooth and reactive bone (A–C). Longitudinal slice through the fused vertebrae shows the substantial overgrowth of reactive bone on the outside of the centra, while the articular surfaces remain largely unaffected (A). Two oblique slices through the vertebrae show the embedded theropod tooth in cross-section and the reactive bone that partially surrounds it (B and C). (Scale bars: A, 20 mm and B and C, 10 mm.)

Fig. 3.

Lateral view of embedded tooth crown showing well-developed blood grooves oriented obliquely toward the base and large, chisel-shaped mesial denticles typical of T. rex (60); (Scale bar: 5 mm.)

Fig. 4.

Graph of tooth dimensions for T. rex, Albertosaurus, and Nanotyrannus, compared with that of the embedded theropod tooth (A and B). When the ICL is plotted against the DCT (A), the three examined taxa are clearly separated, with a large gap existing between T. rex and Albertosaurus, and minor overlap between Albertosaurus and Nanotyrannus. The embedded theropod tooth falls only within the region occupied by T. rex (bold black line in A) and does not overlap with the other two taxa. Graphed ranges of tooth denticles per cm (B) indicates a similar trend, in which the embedded theropod tooth only overlaps T. rex and does not match either Albertosaurus or Nanotyrannus.