STEGOSAURIAN MARTIAL ARTS: A JURASSIC CARNIVORE STABBED BY A TAIL SPIKE, EVIDENCE FOR DYNAMIC INTERACTIONS BETWEEN A LIVE HERBIVORE AND A LIVE PREDATOR

Were carnivorous dinosaurs active predators, killing their own prey, or scavengers depending upon carcasses found dead, or a mixture of both? Today, large herbivores -- buffalo, rhinos, hippos -- often fight back, damaging the attackers. Many dinosaurian herbivores carried horns or spikes or other potentially dangerous weapons. Such armament may have functioned in defense, courtship displays and intraspecific combat. If dinosaurian predators regularly attacked well-armed herbivores, we would expect to find predator skeletons with wounds that can be attributed to particular herbivores.

We have analyzed an adult allosaur skeleton from the Brushy Basin Member of the Morrison Formation, Late Jurassic, Albany County, Wyoming. A stab wound penetrated through the lower pubis, piercing the entire pubic “boot”. A massive infection ate away a baseball-sized sector of the bone; probably this infection spread upwards into the soft tissue attached here, the thigh muscles and adjacent intestines and reproductive organs. Lack of healing in the wound indicates that the allosaur died from the consequences of the strike.

The wound has the shape of a cone. The size and shape match that of stegosaur tail spikes from specimens dug in the same strata. The strike appears to have come from directly below the allosaur. To deliver a vertical blow, a stegosaur would have to twist the tail tip because in normal posture the spikes point outward and backward. Stegosaur tails are unusual: near the hips the tail muscles were massive; functional accessory joints (zygapophyses) and muscle attachments continue far distally to the tail tip. We interpret such tail specializations as providing both power and precision in the direction of the spike trajectory. Therefore we interpret the allosaur as a victim of herbivore defense.