Dinosaur VaultEvery known dinosaur
Allosaurus, Late JurassicMorrison Formation, Wyoming · named 1877
See more pictures

Allosaurus

AL-oh-SORE-us

"different lizard"

Lived
155 to 143 million years ago, Late Jurassic
Diet
Carnivore
Length
about 9.5 m (31 ft)
Weight
about 2 metric tons (2.2 short tons)
Group
Theropods
Found in
United States and Portugal
Named by
Marsh 1877

Size comparison

To scale

Where its fossils were found

The evidence

Today

137 finds

150 million years ago

Map: C. R. Scotese, PALEOMAP

Also reported from Germany.

Habitat

Rivers crossed broad floodplains in the Morrison Formation landscape, with conifers, ferns and horsetails. Stegosaurus, Diplodocus and Camptosaurus lived in this world.

A Dinosaur Vault film

Who Punched a Hole Through This Dinosaur Bone?

An Allosaurus tail bone with a hole straight through it, a Stegosaurus tail spike that fits the wound, and a bitten neck plate that tells the other half of the fight.

Subscribe on YouTube
Plays from YouTube, which may store data on your device. Privacy · Watch on YouTube

Field notes

About Allosaurus

What it was like

Allosaurus was a large, agile hunter with a light, strong skull lined with rows of sharp, serrated teeth. It grew up to about 9.5 meters (31 feet) long and could weigh around 2 metric tons. Its arms were small next to its powerful legs but ended in sharp, curved claws.

It probably preyed on large plant eaters such as stegosaurs and sauropods. Scientists still debate whether Allosaurus hunted alone or sometimes gathered around the same carcass or prey.

Its world

Allosaurus lived from about 155 to 143 million years ago, spanning the Late Jurassic and Early Cretaceous, in what is now the western United States and Portugal. Its bones come mainly from the Morrison Formation, alongside plant eaters like Stegosaurus, Camarasaurus, Brachiosaurus, and Diplodocus, and other hunters such as Ceratosaurus and Torvosaurus. Allosaurus was the most common large predator in this habitat, so its bones turn up wherever the Morrison rock is exposed.

How it was found

Marsh named Allosaurus in 1877. It is one of the best-known Jurassic predators, with about 137 fossil finds recorded, giving paleontologists an unusually full picture of how it looked and moved. Few other dinosaurs from this period are known from so many separate skeletons.

Field gallery

More views of Allosaurus

Scenes reconstructed from the available fossil evidence.

Allosaurus in its habitat, photo 1

1 of 7

Lived alongside

Found in the same rock formations

A rock formation can hold fossils laid down millions of years apart, so not every animal here met Allosaurus.

The evidence

The science behind Allosaurus

Which parts of the picture come from its own bones, and which come from its relatives.

From its own fossils

  • Many skeletons preserve a light, deep skull with serrated teeth and low bony crests above the eyes.
  • Its arms ended in grasping hands with three clawed fingers, and a long tail balanced the body.
  • Young animals had relatively longer lower legs than adults.

Borrowed from relatives

  • Almost the whole skeleton is known from its own bones.
  • Lips covering the teeth are inferred from comparisons with other theropods, including Tyrannosaurus.

Still unknown

  • Its color and the full extent of its skin covering.
  • Whether it hunted alone or cooperated with others.
  • The complete skull and body proportions of young Allosaurus fragilis.

Often drawn wrong

  • The crests sat above the eyes, rather than forming a tall horn on the nose.
  • Its palms faced inward, rather than downward.
  • Its hands had three clawed fingers, rather than the pair seen in Tyrannosaurus.

Discovery timeline

  1. 1877Named itMarsh
  2. 2001How it fedRayfield et al.
  3. 2005Growing upRauhut & Fechner
  4. 2013How it fedSnively et al.
  5. 2020SkullChure & Loewen
  6. 2023Close relativeCullen et al.

Key papers

The research behind what we know of Allosaurus

Close relatives

Other members of Allosauroidea

Sources: Wikidata