The Allosaurus was the dominant large predator of the Late Jurassic period, reigning across North America and parts of Europe approximately 155 to 145 million years ago. This formidable theropod, with Allosaurus fragilis being its best-known species, was a large, bipedal carnivore averaging around 8.5 meters in length. Its success as the apex predator of the Morrison Formation ecosystem depended on a unique combination of physical traits and behavioral strategies. Paleontologists have used scientific evidence to understand what this dinosaur ate and the methods it used to hunt and subdue its massive prey.
Anatomical Adaptations for Predation
The physical structure of Allosaurus was finely tuned for a predatory style that relied on slicing and tearing rather than brute crushing force. The skull was surprisingly light and robust, constructed to withstand significant vertical stress from impacts rather than sustained bite pressure. Biomechanical studies estimate its bite force was relatively weak compared to later giant theropods, suggesting it did not rely on bone-crushing to kill.
The teeth lining its jaws were curved, laterally compressed, and finely serrated, functioning like dozens of tiny steak knives. These serrations were designed to cut through flesh and tissue efficiently, allowing the predator to carve away large chunks of meat. This dentition strategy inflicted massive wounds and blood loss rather than instantaneously crushing the vertebral column of its prey.
The neck muscles were exceptionally powerful, inferred from large muscle attachment sites on the back of the skull and the shape of the neck vertebrae. This musculature allowed for rapid, forceful downward and backward movements of the head, suggesting the head was used actively as a weapon.
The forelimbs, though short, were powerfully built with three digits ending in large, strongly curved, hook-like claws. These claws were functional tools, likely used to grasp, restrain, and anchor itself to struggling prey during an attack. The combination of tearing teeth, a reinforced skull, and powerful grasping arms created a specialized killing machine adapted for large, vulnerable targets.
Identifying the Primary Prey Sources
Allosaurus was an opportunistic carnivore whose diet primarily consisted of the large herbivorous dinosaurs that shared its Late Jurassic habitat in the Morrison Formation. The most common prey were abundant sauropods, such as Apatosaurus and Diplodocus. Fully grown adults were likely too massive to be targeted directly, so Allosaurus preferentially hunted juvenile, sick, or elderly individuals.
Trace fossils provide direct proof of this predator-prey relationship, with numerous sauropod bones bearing bite marks that match the serrated teeth of Allosaurus. These tooth marks are often found on the less meaty portions of the skeleton, suggesting the predator frequently scavenged large sauropod carcasses. Opportunistic feeding also extended to smaller, faster prey like ornithopods, which were likely pursued by younger, more agile Allosaurus.
One of the most iconic interactions documented is between Allosaurus and the armored dinosaur Stegosaurus. Evidence includes an Allosaurus tail vertebra with a partially healed puncture wound matching a Stegosaurus tail spike (thagomizer). Conversely, a Stegosaurus neck plate has been found with an unhealed injury consistent with an Allosaurus bite, indicating these encounters were frequent and violent.
Further evidence of opportunistic feeding comes from the Mygatt-Moore Quarry, where a high percentage of bones bear theropod bite marks, including those on Allosaurus bones themselves. This suggests that during lean times, the predator scavenged the remains of its own kind, a form of cannibalism common in modern large carnivores.
Debates on Hunting Strategy and Social Behavior
The relatively weak bite force of Allosaurus led to the dominant scientific theory known as the “hatchet attack” or “strike-and-tear” strategy. This method proposes that the predator would use its lower jaw as an anchor and slam its robust upper jaw and serrated teeth down onto its prey, driven by its strong neck muscles. The objective was not to crush bone but to deliver massive, repeated blows causing deep, gaping wounds and rapid blood loss.
The powerful neck musculature allowed Allosaurus to quickly rip flesh away from the carcass, similar to how modern birds of prey strip meat. This strategy was effective for taking down large animals without risking the structural integrity of the lightly built skull in a sustained bite. Its moderate speed suggests it was an ambush hunter, aligning with a rapid, violent strike tactic.
The question of whether Allosaurus hunted in coordinated packs remains debated. The Cleveland-Lloyd Dinosaur Quarry in Utah presents an unusual concentration of fossils, with Allosaurus remains outnumbering herbivores three to one. This assemblage has historically been interpreted as a “predator trap,” where a mired herbivore attracted multiple Allosaurus, which then became trapped themselves.
The high number of juvenile and subadult Allosaurus found there is sometimes cited as support for loose group hunting. However, a competing interpretation suggests the quarry represents a drought-induced mass death assemblage, where non-social animals were drawn to a dwindling water source. While a highly coordinated pack structure is not widely supported, their abundance suggests they were highly tolerant of one another, congregating opportunistically around large kills.