Allosaurus was the apex predator of the Late Jurassic Period, dominating its ecosystem the way T-Rex would dominate North America 80 million years later. About 28 feet long, fast, with three-fingered hands ending in long curved claws, Allosaurus hunted Stegosaurus, Brachiosaurus juveniles, Camptosaurus, and any other Jurassic prey it could catch. This guide covers what scientists know about Allosaurus, drawn from one of the most fossil-rich rock formations in North America — the Morrison Formation that produced most of the famous Jurassic dinosaurs.

Quick facts#

Lived: Late Jurassic, about 155 to 145 million years ago
Length: 28 to 32 feet (8.5 to 10 meters)
Height at hip: 9 to 11 feet (3 meters)
Weight: 2 to 4 tons
Diet: Carnivore — large herbivores
Where found: Morrison Formation in western North America (Colorado, Utah, Wyoming, New Mexico)
Defining features: Three-fingered hands with long claws, twin head crests above the eyes, slim athletic build

What Allosaurus looked like#

A 28- to 32-foot predator with a body design optimized for speed and agility rather than raw bite force. Compared to T-Rex (which would dominate North America 80 million years later), Allosaurus was:

Smaller and lighter — about half T-Rex's weight
Faster — better leg proportions for running
Better armed with hands — three fingers per hand with long curved claws (T-Rex had two short fingers)
Less bite force — narrower jaws, less bone-crushing power

Three-fingered grasping hands#

Unlike T-Rex's famously tiny arms, Allosaurus had functional grasping hands with three long-clawed fingers. The claws curve inward, designed for gripping prey. This is part of why Allosaurus is thought of as a more "active" predator than T-Rex — it could engage prey with both jaws and claws.

Head crests#

Two small horn-like ridges above the eyes. Probably used for display rather than fighting — the bone is not strong enough to serve as a weapon. The crests may have been brightly colored in life and helped Allosaurus recognize other Allosaurus.

Slim athletic build#

Allosaurus had a lighter body design than T-Rex. The neck was longer relative to body size, the tail was longer for balance, and the leg-to-body proportions were optimized for pursuit. Top speed estimates: 25 to 30 mph.

What it ate#

Large herbivores of the Late Jurassic, including:

Stegosaurus — fossil evidence (an Allosaurus tail vertebra with a puncture wound matching a Stegosaurus tail spike) confirms direct combat
Camptosaurus — a medium-sized herbivore common in the same rock formations
Young sauropods — adult Brachiosaurus and Diplodocus were too big to hunt, but juveniles were vulnerable
Ornithopod dinosaurs — various other Jurassic herbivores
Possibly carrion — scavenging when opportunity allowed

The hunting strategy was probably ambush-and-bite — using speed to close the gap, then attacking with jaws and clawed hands.

Allosaurus vs Stegosaurus#

The most famous matchup in Late Jurassic North America. They shared the same habitats.

A specimen at the Denver Museum of Nature and Science includes an Allosaurus tail vertebra with a puncture wound shaped exactly like a Stegosaurus tail spike. Another specimen of Stegosaurus shows a healed bite wound from Allosaurus on its neck. Both fossils mean the animals fought, and at least one survived the encounter.

The matchup was probably common. Stegosaurus was a large slow herbivore; Allosaurus was the right size to take it down with effort. Tail spikes were defensive weapons that made Allosaurus pay a price for the attempt. Some Allosaurus survived; some didn't. Some Stegosaurus survived; some didn't. Real predator-prey dynamics, preserved in stone.

Allosaurus vs T-Rex#

The two most famous large theropod predators of North America, separated by 80 million years.

	Allosaurus	Tyrannosaurus Rex
Length	28 to 32 feet	40 feet
Weight	2 to 4 tons	9 tons
Lived	155 to 145 million years ago	68 to 66 million years ago
Hands	3 fingers, long claws, grasping	2 fingers, short
Bite force	Moderate	Strongest of any land animal ever
Speed	25 to 30 mph estimated	12 to 15 mph estimated
Hunting strategy	Active pursuit + claws + bite	Ambush + crushing bite

They never met. Allosaurus and T-Rex are separated by an enormous stretch of time. The dominant predator role in North America shifted between them — Allosaurus dominated the Late Jurassic, then went extinct at the Jurassic-Cretaceous boundary; T-Rex appeared near the end of the Cretaceous, 80 million years later.

Where Allosaurus fossils are found#

Almost exclusively in the Morrison Formation — the Late Jurassic rock formation that stretches across Colorado, Utah, Wyoming, and surrounding states. Multiple complete Allosaurus skeletons have been found here, making it one of the best-studied theropod dinosaurs.

The most famous specimens:

"Big Al" at the Museum of the Rockies — a nearly complete Allosaurus skeleton with multiple healed injuries showing a rough life
Multiple specimens at the Denver Museum of Nature and Science
The Cleveland-Lloyd Dinosaur Quarry in Utah — has produced over 40 Allosaurus skeletons, more than any other site
The Carnegie Museum of Natural History in Pittsburgh

For Florida families: no Allosaurus fossils in Florida. Late Jurassic North American dinosaurs are a Mountain West story.

How scientists know about Allosaurus#

The Allosaurus fossil record is one of the most complete for any large dinosaur.

Multiple complete skeletons — over 60 individuals studied
Bone microstructure — growth rates, age at death
Healed injuries — the "Big Al" specimen had multiple healed injuries showing rough lifestyle
Tooth wear patterns — confirmed carnivorous diet
Bite marks on prey fossils — direct evidence of hunting Stegosaurus, Camptosaurus
Trackways — preserved footprints confirming walking gait

At a Jurassic Petting Zoo event#

Allosaurus is not currently in our regular fleet, but the science we teach at our school events covers the Late Jurassic ecosystem extensively — including Allosaurus's role as apex predator alongside Stegosaurus and the sauropods. Kids learning paleontology often find Allosaurus more interesting than T-Rex once they learn how the predator role shifted across the Mesozoic.

Frequently asked questions#

Was Allosaurus the biggest dinosaur of its time?#

In North America during the Late Jurassic, yes — Allosaurus was the largest known predator. Globally during the same period, other large theropods existed (Saurophaganax may have been larger; the relationship between Saurophaganax and Allosaurus is debated). Allosaurus was the dominant predator in its specific ecosystem.

Did Allosaurus hunt in packs?#

Probably not in coordinated packs. Some Allosaurus bone bed deposits show multiple individuals together, suggesting loose social behavior. But organized cooperative hunting (like wolves) is not strongly supported by the evidence.

How fast could Allosaurus run?#

Estimated 25 to 30 mph in sprints. Faster than T-Rex (which could not really run at all due to its weight). Allosaurus's leg structure was built for active pursuit.

Did Allosaurus have feathers?#

Probably partial feathers, at least as a juvenile. Allosaurus is a theropod, the dinosaur group that included most feathered species. No direct fossil evidence of Allosaurus feathers has been found, but related species had them.

What killed Allosaurus?#

Allosaurus went extinct at the Jurassic-Cretaceous boundary, about 145 million years ago. The cause was environmental change — shifting climate, ecosystems restructuring as the continents continued to drift. New predator species (different from Allosaurus) became dominant in the Cretaceous.

Where can I see an Allosaurus skeleton?#

The Museum of the Rockies in Bozeman, Montana (Big Al specimen) and the Denver Museum of Nature and Science have some of the best Allosaurus displays. The Cleveland-Lloyd Dinosaur Quarry in Utah (where many specimens were found) is also a notable site.

Bring the Jurassic to life#

For South Florida schools and families exploring the Jurassic Period, our school events cover the full Mesozoic ecosystem — including the predator-prey dynamics that made Allosaurus the apex of its time. Check date availability.

Allosaurus: The Apex Predator of the Jurassic