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Science & Nature • Paleontology

Allosaurus

Allosaurus is a genus of large carnivorous theropod dinosaurs that lived during the Late Jurassic Period.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 27, 2026|2 min read| Fact-checked

Allosaurus is a genus of large carnivorous theropod dinosaurs that lived during the Late Jurassic Period. It is among the best-known dinosaurs from North America, especially from fossils in the Morrison Formation of the western United States.

Description

Allosaurus was a large meat-eating theropod dinosaur that walked on two legs. It had a big head, sharp serrated teeth, short arms with three fingers, and distinctive horns above the eyes.

Fossils and distribution

Most well-known fossils come from the Morrison Formation of western North America, particularly Utah and Colorado. Fossils have also been reported from other parts of North America and from countries outside North America, including Tanzania and Germany.

Classification and naming

Allosaurus is a genus within the theropod dinosaurs. The name is usually translated as “different lizard,” reflecting unusual vertebrae noted when it was first described in 1877.

Paleobiology

Allosaurus was an apex or near-apex predator in its ecosystem and probably fed on smaller dinosaurs and other prey. Its abundance in quarry sites has made it one of the best-studied large predatory dinosaurs.

Key facts

  • Allosaurus was a large bipedal predator with three-fingered hands and a long tail for balance.
  • The genus is best known from Late Jurassic fossils in the western United States, especially Utah and Colorado.
  • Allosaurus fragilis is the best-known species and is common in the Morrison Formation.
  • The name Allosaurus means “different lizard.”
  • Some specimens suggest a length of roughly 8.5 metres, with larger estimates approaching 12–13 metres.
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Canadian context

Allosaurus is relevant to Canadian readers through museum collections, dinosaur education, and comparisons with Canadian Late Jurassic and Cretaceous fossil sites. It is also a standard reference genus in paleontology and natural-history curricula.

Frequently asked questions

What does Allosaurus mean?
Allosaurus is commonly translated as “different lizard.”
When did Allosaurus live?
Allosaurus lived during the Late Jurassic, roughly 155–145 million years ago.
What did Allosaurus eat?
It was a carnivore that likely hunted smaller dinosaurs and may also have scavenged.
Where have Allosaurus fossils been found?
Fossils are especially common in western North America, including Utah and Colorado, and have also been reported from Tanzania and Germany.
Who named Allosaurus?
It was first named by Othniel Charles Marsh in 1877.

References

  1. National Geographic Kids — https://kids.nationalgeographic.com/animals/prehistoric/facts/allosaurus
    Supports: Late Jurassic age, bipedal theropod status, fossil locations, general size
  2. Live Science — https://www.livescience.com/24815-allosaurus.html
    Supports: Late Jurassic dating, Utah state fossil, size estimates, Cleveland-Lloyd Quarry significance
  3. Natural History Museum — https://www.nhm.ac.uk/discover/dino-directory/allosaurus.html
    Supports: Late Jurassic range, North American distribution, anatomy
  4. Encyclopaedia Britannica — https://www.britannica.com/animal/Allosaurus
    Supports: Genus description, Late Jurassic age, key fossil localities
  5. U.S. National Park Service — https://www.nps.gov/dino/learn/nature/allosaurus-fragilis.htm
    Supports: Allosaurus fragilis as common Morrison Formation theropod