Allosaurus fragilis was the apex predator of the Late Jurassic epoch in North America, dominating the food web of the Morrison Formation around 150 million years ago. This formidable theropod, whose name means “different lizard,” is one of the most well-represented large carnivorous dinosaurs in the fossil record. Its abundance, particularly in sites like the Cleveland-Lloyd Dinosaur Quarry, has allowed detailed studies into its physical capabilities, diet, and hunting strategies. Understanding what Allosaurus ate requires piecing together evidence from its specialized anatomy, the scars left on the bones of its contemporaries, and modern biomechanical modeling. This scientific detective work reveals a predator with a unique approach to tackling the massive herbivores of its time.
The Hunter’s Toolkit: Anatomical Evidence of Predation
The body structure of Allosaurus provides direct clues about its role as a carnivore. Its teeth were distinctively blade-like, recurved, and serrated (ziphodont dentition), perfectly suited for slicing through flesh and causing immense blood loss. These teeth were replaced frequently, ensuring a constantly sharp set of cutting tools, suggesting a feeding style focused on tearing soft tissue rather than crushing bone.
Biomechanical analyses indicate the Allosaurus skull had a relatively low bite force (5,494 to 8,724 Newtons) compared to later theropods like Tyrannosaurus rex. This lower force suggests the animal did not rely on a crushing bite to kill its prey. Despite the weak bite, the skull was robust and strong, especially in the upper jaw, capable of withstanding considerable vertical stress. This combination points toward a specialized, high-impact feeding method.
The neck muscles were powerful and flexible, attaching to the back of the skull to allow the head to be driven downward or pulled backward aggressively. This musculature was essential for delivering deep, slashing wounds and ripping off chunks of flesh. The forelimbs were strong and relatively long for a large theropod, ending in three fingers tipped with large, curved claws. These forelimbs were used primarily for grasping and stabilizing struggling prey.
The hind limbs were built for speed and agility, suggesting a capacity for active pursuit. This anatomical profile—including a strong skull, serrated slicing teeth, powerful neck, and grasping forelimbs—shows a predator adapted to repeated strikes and rapid dismemberment.
The Menu: Fossil Evidence Identifying Specific Prey
Direct fossil evidence confirms the animals that formed the diet of Allosaurus. The most common evidence comes from pathology and bite marks left on the bones of other dinosaurs. These marks, characterized by the distinctive size and spacing of Allosaurus teeth, are found on various large herbivores across the Morrison Formation.
Evidence of interaction with the plated dinosaur Stegosaurus is well-documented. One Allosaurus tail vertebra was discovered with a partially healed, circular puncture wound that perfectly matches the size and shape of a Stegosaurus tail spike (thagomizer). This injury suggests the Allosaurus survived a close-quarters encounter, confirming that Stegosaurus was a dangerous target.
Bite marks are also frequently found on the bones of massive sauropods, such as Apatosaurus and Diplodocus, and on smaller ornithopods like Camptosaurus. Given the immense size of adult sauropods, Allosaurus likely focused on juveniles, the sick, or the already dead. The number of sauropod remains suggests that carrion from these giants provided a significant, accessible food source.
The Mygatt-Moore Quarry in Colorado yielded a high concentration of bones bearing theropod bite marks, including those of Allosaurus. A small percentage of Allosaurus bones at this site also showed bite marks made by other large theropods, likely other Allosaurus individuals. This evidence suggests that Allosaurus engaged in scavenging and opportunistic cannibalism, feeding on their own kind after death.
Method of Attack: Interpreting Hunting Strategies
The unique anatomy of Allosaurus led to the “Hatchet Strike” hypothesis. This theory suggested the predator would open its jaws wide and use its powerful neck muscles to deliver a massive, slashing blow to its prey, like an axe striking downward. Biomechanical modeling initially supported the idea that the skull could withstand the vertical forces of such an impact.
More recent analysis suggests this high-impact, slamming method was too risky and likely unsustainable due to potential lower jaw interference and excessive tooth breakage. The current consensus favors a more nuanced “slash and tear” or “grip and rip” strategy. In this revised view, Allosaurus used its strong neck and powerful forelimbs to stabilize or grapple with its prey.
The predator would drive its blade-like teeth deep into the prey’s flank or limbs and pull back, using its body weight and neck strength to rip off large strips of flesh. This method, similar to the feeding technique of a modern Komodo dragon, would cause massive trauma and blood loss, eventually incapacitating the herbivore. The skull’s high strength was an adaptation for resisting the forces of pulling and thrashing during this feeding action.
Fossil assemblages, such as the numerous Allosaurus individuals found at the Cleveland-Lloyd Quarry, fuel the debate over social hunting. Some scientists interpret this congregation as evidence of a pack trapping prey. Others see it as a “predator trap,” where multiple Allosaurus were drawn to scavenge mired or deceased animals. The numerous healed fractures and injuries found on Allosaurus skeletons indicate its life involved dangerous, close-contact encounters with large prey.