Category: Dinosaur

Allosaurus (Al-loh-sore-us) lived in the Late Jurassic of North America, around 150 million years. It is the most common predator from the area known as the Morrison Formation.



Genera and Species

Theropoda, Carnosauria, Allosauridae

Allosaurus (“Different Lizard”)

A. fragilis, A. europaeus, A. amplus, A. lucasi

Senior synonyms:
Allos. atrox, Allos. whitei , Allos. Lucaris, A.europaeus), Creosaurus atrox, Labrosaurus ferox, L. fragilis, L. lucaris, Antrodemus fragilis, Antro. lucaris, Antro. atrox, Antro. trihedrodon, Camptonotus amplus, Camptosaurus amplus, Laelaps trihedrodon, possibly Dryptosaurus trihedrodon, Hypsirophus trihedrodon and Apatodon mirus.


Allosaurus was a large theropod predator, typical in body shape with long powerful hind legs, a long tail and a large head full of sharp teeth. It had two small bony crests above and ahead of their eyes, and two smaller ones behind them and a low, narrow, bony ridge from eyes to snout. Its skull was deep, and the jaws contained an impressive array of flattened, serrated teeth. The forelimbs were muscular and ended in 3 fingered hands with powerful grasping claws, while the hind limbs were massive but capable of rapid movement.


Length 10 - 12 m (33 - 40 ft).

Weight 1 - 1.7 tons.


It probably preyed upon the smaller camarasaurs and diplodocids along with stegosaurs and camptosaurs. Fossil evidence from bones of Ceratosaurus and Torvosaurus show Allosaur tooth marks, so they could have suppressed other carnivores much like lions do today. Footprint evidence shows up to three allosaurs patrolling the same area, meaning they may have hunted in groups.

History of Discovery

Discovered by Othniel Charles Marsh in 1877 and known from 3 complete skulls, partial and complete skeletons of at least 60 animals, and many other isolated bones.


Allosaurus lived in what is now Utah and Colorado, in semi-arid plains with a short rainy season crossed by braided rivers. It lived alongside many other carnivorous dinosaurs including Ceratosaurus and Torvosaurus, as well as large sauropods including Camarasaurus, Brachiosaurus, Apatosaurus and Diplodocus, to name just a few.


  1. Paul, G. (2016). The Princeton Field Guide to Dinosaurs, 2nd Edition. Princeton, New Jersey: University Press Princeton.
  2. Worth, G. (1999). The Dinosaur Encyclopaedia (pp. 10-12). Scarborough, Western Australia: HyperWorks Reference Software.