Allosaurus

Allosaurus is an iconic Mesozoic carnivore and the most frequently collected large theropod after Tyrannosaurus rex. Adults typically reached 8.5–12 m in length and weighed around 2 tonnes. The largest specimens, including those referred to Saurophaganax or A. maximus, approached 12 m. Its long skull was narrow when viewed from above but deep from the side. It featured diagnostic paired lacrimal horns above and slightly in front of the eyes, which were likely covered in keratin for display. The blade-like teeth were flattened side-to-side, finely serrated, and replaced throughout the animal's life.

The forelimbs had three functional fingers tipped with large, recurved claws. The thumb claw was especially prominent and often shows heavy wear, suggesting it was used frequently for handling prey. Because its hindlimbs were relatively gracile, researchers believe Allosaurus relied on fast walking and short bursts of speed rather than sustained sprinting. The tail was held horizontally to provide a steady counterbalance.

At least three species are widely recognised today: A. fragilis (the type), A. jimmadseni (a slightly older morphotype described in 2020), and A. europaeus from Portugal. Some researchers also accept A. lucasi and A. anax. Saurophaganax maximus might represent a fourth, larger species or a separate genus entirely.

Allosaurus shared its Morrison Formation habitat with Stegosaurus, Diplodocus, Apatosaurus, Brachiosaurus, Camarasaurus, Ceratosaurus, and Torvosaurus. Evidence of direct interaction with these herbivores exists in the form of tooth-marked bones and a famous Allosaurus tail vertebra pierced by a Stegosaurus thagomizer spike. According to skull biomechanics (Rayfield et al. 2001), the predator may have used its head like a hatchet, delivering open-mouth strikes to pull flesh away instead of crushing bone. Its bite force was relatively modest at 3,500–8,000 N compared to tyrannosaurids, but the slashing action was an effective compensation.

• Big Al (MOR 693, Allosaurus jimmadseni) — Museum of the Rockies; subject of Walking with Dinosaurs: Ballad of Big Al. 19 healed pathologies indicating a hard life.
• Big Al II (SMA 0005) — Sauriermuseum Aathal, Switzerland; remarkably complete.
• Cleveland-Lloyd Quarry assemblage — at least 46 individuals from one site, multiple institutions.
• AMNH 5753 — historic Allosaurus mounted over an Apatosaurus carcass in Charles Knight's iconic 1903 reconstruction.

Species-level taxonomy is the active question: how many Allosaurus species exist (3–6 depending on author), and whether Saurophaganax belongs in the genus. A. jimmadseni (Chure & Loewen 2020) is the most recent named species. The functional role of the lacrimal horns (display vs combat vs both) is debated but the consensus tilts toward display. The ecology of the Cleveland-Lloyd predator trap remains an open question.

Allosaurus was the apex predator in Fantasia (1940), where it fights a Stegosaurus, and in The Lost World (1925). Charles Knight's Allosaurus and Brontosaurus paintings (1897 onward) defined dinosaur paleoart for half a century. Walking with Dinosaurs: The Ballad of Big Al (2000) gave it its own BBC documentary feature.

• allosauridae
• theropoda
• stegosaurus
• diplodocus
• apatosaurus
• camarasaurus

• Madsen, J. H. (1976). Allosaurus fragilis: a revised osteology. Utah Geological Survey Bulletin, 109.
• Foster, J. (2007). Jurassic West: The Dinosaurs of the Morrison Formation. Indiana University Press.
• Chure, D. J., & Loewen, M. A. (2020). Cranial anatomy of Allosaurus jimmadseni. PeerJ, 8, e7803.
• Rayfield, E. J., et al. (2001). Cranial design and function in a large theropod dinosaur. Nature, 409, 1033–1037.
• Bakker, R. T., & Bir, G. (2004). Dinosaur crime scene investigations. In Feathered Dragons, Currie et al. (eds.).