A BITE-MARKED BONE FROM THE LATE CRETACEOUS HELL CREEK FORMATION MAY ILLUSTRATE TYRANNOSAURUS FEEDING BEHAVIOR

Although bite marks in fossil bones are often overlooked, they are valuable paleontological resources because they provide evidence of real-world ecological interactions, even when ascertaining the true identity of the trace maker or the recipient of the bite is difficult or impossible. Here we describe an isolated partial dinosaur vertebra from the Maastrichtian Hell Creek Formation with multiple bite marks, discovered as float during prospecting northeast of the town of Baker, Montana. The bone resembles a caudal hadrosaurid (possibly Edmontosaurus) vertebra, but it is distorted, its surface is heavily eroded, and it is missing its neural arch, neural spine and transverse processes. The centrum bears more than twenty subparallel punctures and score marks on its face and side, concentrated ventrally, many of which penetrate the bone cortex. Several of the score marks appear to correspond with four closely-spaced large (5 – 10 mm wide, 2 – 18 mm deep) punctures that pierce the face of the centrum. Some punctures are elongated, while others are roughly circular. Several punctures have V-shaped bottoms. The depths of some of the score marks vary along their length, likely due to changes in the amount of force applied to the bone during the duration of the bite. Biting appears to have led to cracks in the centrum both across its face and along its side. Although alteration of the bone during burial and after exposure makes positive identification challenging, the location, size and morphology of the punctures implies that the trace maker was likely a Tyrannosaurus. The arrangement of marks on the bone indicates that they were made during a post-mortem feeding event after parts of the vertebral column had been disarticulated and the face of the centrum had been exposed. Other bite-marked bones from the Hell Creek Formation have shown evidence of carcass-dismembering behavior by feeding Tyrannosaurus. The marks on this bone suggest that the carnivore dragged its teeth along the side of the centrum, over the rim, then across its face, applying varying amounts of bite force during the process, possibly in an attempt to gain purchase on the vertebra during an effort to dismember the carcass.