EVIDENCE FOR TYRANNOSAURID FEEDING BEHAVIOR FROM HADROSAURIAN DINOSAUR REMAINS IN THE AGUJA FORMATION (UPPER CRETACEOUS), BIG BEND NATIONAL PARK, TEXAS

Preserved bones of a large hadrosaur from the upper shale member of the Aguja Formation show extensive covering of bite marks from a tyrannosaurid dinosaur. Aside from the hadrosaur hind limb elements recovered (distal tibia, astragalus, metatarsals, and pedal phalanges), only a broken tyrannosaur tooth crown is known from the collection site (TMM 43679). All of the hadrosaur bones, even the phalanges, have bite marks on multiple sides indicating that the carcass was completely dismembered during the process of feeding. The width and depth of the bite marks suggest that they were made by one or more adult tyrannosaurs. Bite marks on the shafts of the limb bones consist mostly of long, curvilinear gouges at varied angles that do not fully penetrate the thick cortical tissue. The gouges are not in parallel series and are compatible with ‘raking’ of large lateral dentary or maxillary teeth across the bone surfaces multiple times. Bite marks on the articular surfaces of the bones are instead more conical or ‘U-shaped’ punctures that penetrate more deeply into the cancellous tissue. These marks are consistent with bites made by anterior premaxillary teeth. Preservation of the hind limb elements in isolation suggest that they were removed from the carcass and brought to a separate site for feeding. The feet have a much lower muscle to bone ratio in comparison to the rest of a hadrosaur carcass, and so the thorough effort on the part of a carnivore to remove all flesh from these elements may record unusual behavior, perhaps brought about by food scarcity and desperation.