Allosaurus skull SDNHM
Replica of Allosaurus skull (San Diego Natural History Museum).
Conservation status
Extinct (fossil)
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Superorder: Dinosauria
Order: Saurischia
Suborder: Theropoda
Infraorder: Carnosauria
Family: Allosauridae
Genus: Allosaurus
Marsh, 1877
  • A. fragilis type
  • A. atrox (Marsh, 1878) Paul, 1987
  • A. europaeus Mateus et al., 2006
  • A. "jimmadseni" Chure, 2000 vide Glut, 2003

Allosaurus was a large bipedalcarnivorous dinosaur up to 12 m (39 ft) long. It was named 'different lizard' because its vertebrae were different from those of all other dinosaurs. The name comes from the Greek allos/αλλος, meaning 'strange' or 'different' and saurus/σαυρος, meaning 'lizard' or 'reptile'.[1] It was the most common large predator in what is now North America, 155 to 145 million years ago, in the late Jurassic period. It shared the landscape with several genera of giant sauropods such as Apatosaurus, Diplodocus and Camarasaurus as well as other herbivores such as Stegosaurus and Camptosaurus, all of which may have been potential prey.

Allosaurus BW

life restoration of Allosaurus fragilis

More scant finds of a smaller species similar to Allosaurus and dating from the Early Cretaceous of North America and Australia, indicate that this versatile hunter might have survived the mass extinction at the end of the Jurassic, 144 MYA. Fukuiraptor from the Early Cretaceous of Japan has been shown to be an allosaurid[2] and may be the same animal as the Australian Allosaurus.



A replica Allosaurus skeleton in Canterbury Museum, Christ church, New Zealand. The current view is that the animal normally stood in a more horizontal position.

Allosaurus was a typical large theropod, with an average length of ~9 meters (~30 feet), having a massive skull on a short neck, a long tail and reduced forelimbs. Its most distinctive feature was a pair of blunt horns, just above and in front of the eyes. Although short in comparison to the hindlimbs, the forelimbs were massive and bore large, eagle-like claws. The skull showed evidence of being composed of separate modules, which could be moved in relation to one another, allowing large pieces of meat to be swallowed. The skeleton of Allosaurus, like other theropods, displayed bird-like features, such as a furcula (wishbone) and neck vertebrae hollowed by air sacs.


Allosaurus is the most common theropod in the vast tract of dinosaur-bearing rock in the American Southwest known as the Morrison Formation. Remains have been recovered in Montana, Wyoming, South Dakota, Colorado, Oklahoma, New Mexico and Utah, in the United States. There have also been finds in Portugal. Allosaurus shared the Jurassic landscape with several other theropods, including Ceratosaurus and the massive Torvosaurus.

Allosaurus-fossilized skull

Allosaurus skull from Dinosaur National Monument, still partially encased in matrix.

A famous fossil bed can be found in the Cleveland Lloyd Dinosaur Quarry in Utah. This fossil bed contains over 10,000 bones, mostly of Allosaurus, intermixed with the remains of other dinosaurs, such as Stegosaurus and Ceratosaurus. It is still a mystery how the remnants of so many animals can be found in one place. The ratio of fossils of carnivorous animals over fossils of plant eaters is normally very small. Findings like these can be explained by pack hunting, although this is difficult to prove. Another possibility is that the Cleveland Lloyd site formed a 'predator trap', similar to the La Brea Tar Pits, that caused large numbers of predators to become mired in an inescapable sediment.[1]

"Big Al"

One of the more significant finds was the 1991 discovery of "Big Al" (MOR 593), a 95% complete, partially articulated, juvenile specimen that measured 8 meters (26 feet) in length. Nineteen bones were broken or showed signs of infection, which probably contributed to Big Al's death. It was featured in "The Ballad of Big Al", a special programme in the BBC's Walking with Dinosaurs series. The fossils were excavated near Shell, Wyoming by the Museum of the Rockies and the University of Wyoming Geological Museum. This skeleton was initially discovered by a Swiss team, led by Kirby Siber. The same team later excavated a second Allosaurus, "Big Al Two", which is the best preserved skeleton of its kind to date.

Classification and history

The first Allosaurus fossil to be described was a 'petrified horse hoof' given to Ferdinand Vandiveer Hayden in 1869, by the natives of Middle Park, near Granby, Colorado. It was actually a caudal vertebra (a tail bone), which Joseph Leidy tentatively assigned first to the Poekilopleuron genus and later to a new genus, Antrodemus.[3] However, it was Othniel Charles Marsh who gave the formal name Allosaurus fragilis to the genus and type species in 1877,[4] based on much better material, including a partial skeleton, from Garden Park, north of Cañon City, Colorado.

The species epithet fragilis is Latin for 'fragile'. Both refer to lightening features in the vertebrae.

It is unclear how many species of Allosaurus there were. The material from the Cleveland Lloyd Dinosaur Quarry specimen is much smaller and more lightly-built than the huge and robust Allosaurus from Brigham Young University's Dry Mesa Quarry. One species of Allosaurus has been described from Portugal, A. europaeus.[5]

Allosaurid relatives

  • Fukuiraptor is an early Cretaceous theropod from Japan thought to be an Allosaurid.
  • An allosaurid astragalus (ankle bone) was found at Cape Patterson, Victoria (Australia in early Cretaceous beds in Southeastern Australia. This is notable as this part of Australia lay within the Antarctic Circle at the time.

In popular culture

Allosaurus is the official state dinosaur of Utah, in the United States.


The Allosaurus "Big Al", as depicted in the BBC Walking With Dinosaurs special The Ballad Of Big Al.

Gwangi vs Styracosaurus

Gwangi, an Allosaurus from the Ray Harryhausen film "The Valley of Gwangi", fights and kills a Styracosaurus.

Along with Tyrannosaurus, Allosaurus has come to represent the quintissential carnivorous dinosaur in popular culture. Allosaurus has featured in the following films:

Allosaurus is top predator in both Arthur Conan Doyle's novel, The Lost World, and the 1925 film adaptation (not to be confused with Tyrannosaurus).

One Million Years BC

The Valley of Gwangi (Gwangi is technically meant to be an Allosaurus but Ray Harryhausen based his model for the creature on Tyrannosaurus. Harryhausen often confuses the two, stating in a DVD interview "They're both meat eaters, they're both Tyrants... one was just a bit larger than the other.")

The main hero of Dinosaucers, "Allo", is an evolved Allosaurus.

Fran Sinclair of Dinosaurs (TV series) is mentioned on the show and a number of merchandise packaging as being an Allosaurus.

An Allosaurus named Santo was the main character of an Age of Reptiles comic, The Hunt. He was pitted against a pack of Ceratosaurus.

Calvin in the comic strip Calvin and Hobbes often imagines himself as an Allosaurus in his "dinosaur" fantasies.

It appears in the second and fifth episodes of Walking with Dinosaurs. As the main enemy of Diplodocus in the second episode, one injures the main character, a female, by taking a deep bite out of her back. A dwarf (Australian) species appears in the fifth episode, as the main predator of Leaellynasaura, killing and eating the leading Leaellynasaura female.

The Walking With Dinosaurs special The Ballad of Big Al chornicles the life of Big Al.

Allosaurus appear in When Dinosaurs Roamed America, killing a Ceratosaurus and feasting on a wounded Apatosaurus.

Allosaurus appears in the children's television series Land of the Lost (1974 TV series) 1974-1976.


  1. Liddell & Scott (1980). Greek-English Lexicon, Abridged Edition. Oxford University Press, Oxford, UK. ISBN 0-19-910207-4.
  2. Currie, P.J. & Y. Azuma, 2006. New specimens, including a growth series, of Fukuiraptor (Dinosauria, Theropoda) from the Lower Cretaceous Kitadani Quarry of Japan. J. Paleont. Soc. Korea 22(1): 173-193.
  3. Leidy J (1870). Remarks on Poicilopleuron valens, Clidastes intermedius, Leiodon proriger, Baptemys wyomingensis, and Emys stevensonianus. Proc. Acad. Nat. Sci. Philadelphia 1870: 3-5
  4. Marsh OC. (1877). Notice of new dinosaurian reptiles from the Jurassic formation. American Journal of Science and Arts 14:514-516
  5. Mateus, O., Walen, A., and Antunes, M.T. (2006). "The large theropod fauna of the Lourinha Formation (Portugal) and its similarity to that of the Morrison Formation, with a description of a new species of Allosaurus." New Mexico Museum of Natural History and Science Bulletin, 36.

External links

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