| Field | Information |
|---|---|
| Species | Allosaurus fragilis — Saurischia, Allosauridae |
| Period | Late Jurassic, 155–145 Ma |
| Diet | Carnivorous — large herbivorous dinosaurs |
| Key prey evidence | Tooth marks on sauropod and ornithopod bones |
Quick Answer:Allosaurus was a carnivorous theropod that fed primarily on herbivorous dinosaurs within the Morrison Formation ecosystem. Fossil evidence directly links it to feeding on sauropods and other herbivorous dinosaurs through tooth-marked bones and shed teeth found at feeding sites, while anatomical and ecological evidence suggests it likely functioned as both an active predator and an opportunistic scavenger.
The bones of Allosaurus fragilis prey tell a story that teeth alone cannot. Fossil evidence from across the Morrison Formation records the direct encounter between this predator and the largest animals of the Jurassic — preserved in the marks left on bone long after the flesh was gone.
What Did Allosaurus Eat?
What Allosaurus ate included a range of large to very large herbivorous dinosaurs documented across the Morrison Formation. The best direct evidence comes from tooth marks matching Allosaurus dental morphology found on the bones of multiple prey species. Allosaurus occupied the apex predator role in its ecosystem and likely targeted prey across a range of sizes depending on availability and opportunity.
Primary prey confirmed or strongly inferred from fossil evidence:
- Sauropods — including Diplodocus, Brachiosaurus, and Camarasaurus; tooth marks on sauropod limb bones and vertebrae are documented from multiple Morrison Formation sites
- Stegosaurus — tooth-marked Stegosaurus bones have been reported; the two species are consistently co-recovered from the same formation.
- Camptosaurus — smaller ornithopod prey, likely more accessible targets than large sauropods
- Dryosaurus — another ornithopod component of the Morrison fauna plausibly taken as prey
- Juvenile and subadult dinosaurs — smaller individuals of otherwise large species would have represented lower-risk targets.
Evidence for Allosaurus Predation
Tooth Marks on Bone
Fossil evidence shows Allosaurus tooth marks on the bones of multiple prey species, providing direct confirmation of feeding behaviour rather than reliance on inference alone. Documented cases include serrated bite marks consistent with Allosaurus dental morphology on sauropod ribs and limb elements. Shed Allosaurus teeth recovered at the same sites further confirm feeding rather than incidental contact.
The Cleveland-Lloyd Quarry Evidence
The Cleveland-Lloyd Dinosaur Quarry in Utah has produced the world’s largest concentration of Allosaurus remains from a single locality, making it one of the most important sites for understanding this predator’s biology and ecology. Fossil evidence from the quarry has been interpreted under several competing hypotheses, including the possibility of a predator trap in which distressed or trapped animals attracted multiple carnivores over time. The unusually high concentration of Allosaurus remains relative to other taxa remains a notable feature of the site, and its precise formation history continues to be actively debated.
Scavenging Alongside Active Predation
Comparison with modern large carnivores suggests Allosaurus was likely both an active predator and an opportunistic scavenger. The distinction between predation and scavenging is difficult to establish from bone marks alone. Inferred from the ecological patterns of modern apex predators, Allosaurus most likely took live prey when available and exploited carcasses of animals it did not kill.
Trophic Role in the Morrison Formation
Allosaurus fragilis was one of the principal large predators of the Morrison Formation ecosystem and is widely regarded as occupying an apex predatory role across much of its range. Fossil evidence shows it co-occurred with multiple large herbivorous dinosaur species across a broad geographic distribution. The abundance of Allosaurus remains at sites such as Cleveland-Lloyd, together with its anatomical adaptations for active predation, supports its interpretation as a major top-level carnivore within Late Jurassic North American ecosystems. The mechanics of how Allosaurus subdued prey — including jaw function and attack behaviour — are explored in the dedicated post on Allosaurus bite force and hunting mechanics.
Related and Contemporary Species
- Ceratosaurus nasicornis — a smaller Morrison Formation predator that may have competed with juvenile Allosaurus for smaller prey items
- Torvosaurus tanneri — a large contemporary theropod whose dietary overlap with Allosaurus is inferred from shared formation and size range
- Diplodocus longus — a large sauropod and likely prey species; tooth mark evidence links Allosaurus feeding to this genus
- Stegosaurus stenops — an herbivore with documented bite mark evidence suggesting it was taken as prey by Allosaurus
- Camptosaurus dispar — a smaller ornithopod co-occurring with Allosaurus in the Morrison Formation, likely taken as prey.
Frequently Asked Questions
Is Allosaurus a meat-eater?
Yes. Allosaurus was a carnivorous theropod, with fossil evidence supporting a diet based on other animals. Tooth marks consistent with Allosaurus dentition have been documented on the bones of herbivorous dinosaurs, including sauropods and ornithopods, supporting its role as a large predatory carnivore in the Morrison Formation ecosystem.
Did Allosaurus hunt alone or in groups?
Whether Allosaurus hunted alone or in groups remains scientifically unresolved. The concentration of multiple individuals at sites such as Cleveland-Lloyd Dinosaur Quarry has been cited as possible circumstantial evidence for social behaviour, but alternative taphonomic explanations — including non-behavioural accumulation processes — remain plausible. Comparisons with modern large carnivores provide possible ecological analogies, but no direct fossil evidence confirms coordinated group hunting in Allosaurus.
Did Allosaurus eat sauropods?
Yes. Fossil evidence indicates that Allosaurus fed on sauropods, with tooth marks consistent with its dentition documented on Morrison Formation sauropod bones, including Diplodocus and Camarasaurus. Whether this feeding primarily involved active predation, scavenging, or opportunistic attacks on vulnerable individuals remains an active area of scientific interpretation.
Note: Site formation hypotheses for Cleveland-Lloyd Quarry and the extent of group hunting behaviour in Allosaurus are active areas of research. Details reflect current scientific consensus but may be revised as new evidence emerges.
Conclusion
Allosaurus was a confirmed apex predator whose diet included some of the largest animals ever to walk the Morrison Formation. Fossil evidence places it in direct feeding contact with sauropods, stegosaurs, and ornithopods. Its trophic role was dominant, its feeding evidence direct, and its dietary range broad enough to include both active prey and opportunistic carrion.
References
Peer-Reviewed Literature
Foster, J.R., 2003. Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. New Mexico Museum of Natural History and Science Bulletin, 23, pp.1–95.
Hanna, R.R., 2002. Multiple injury and infection in a sub-adult theropod dinosaur, Allosaurus fragilis, with comparisons to allosaur pathology in the Cleveland-Lloyd Dinosaur Quarry collection. Journal of Vertebrate Paleontology, 22(1), pp.76–90. https://doi.org/10.1671/0272-4634(2002)022[0076:MIAIAS]2.0.CO;2
Madsen, J.H., 1976. Allosaurus fragilis: A Revised Osteology. Utah Geological and Mineral Survey Bulletin 109. Salt Lake City, Utah.
Rayfield, E.J., Norman, D.B., Horner, C.C., Horner, J.R., Smith, P.M., Thomason, J.J., and Upchurch, P., 2001. Cranial design and function in a large theropod dinosaur. Nature, 409, pp.1033–1037. https://doi.org/10.1038/35059070
Roach, B.T. and Brinkman, D.L., 2007. A reevaluation of cooperative pack hunting and gregariousness in Allosaurus. Bulletin of the Peabody Museum of Natural History, 48(1), pp.103–138. https://doi.org/10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2
Monographs and Reference Works
Fastovsky, D.E. and Weishampel, D.B., 2016. Dinosaurs: A Concise Natural History. 3rd ed. Cambridge University Press.
Paul, G.S., 2016. The Princeton Field Guide to Dinosaurs. 2nd ed. Princeton University Press.
Databases and Online Resources
Paleobiology Database, 2026. Allosaurus fragilis occurrence and specimen data. Available at: https://paleobiodb.org [Accessed 19 May 2026].
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