Skeletal reconstruction of Allosaurus fragilis

  • Allosaurus fragilis Marsh, 1877
  • ? Allosaurus maximus Chure, 1995
  • ? Allosaurus tendagurensis Janensch, 1925

Allosaurus (Greek for different type of lizard ) is a genus of theropod dinosaurs. She lived in the age of the Upper Jurassic and is detected in North America and Southern Europe by finds. Earlier asked to the genus finds from the Upper Jurassic of Tanzania and the Lower Cretaceous of Australia can not be assigned safely.

Othniel Charles Marsh gave the first description in 1877 of the genus named after the anatomy of the vertebral bones that were designed differently than the previously known dinosaur vertebrae.

Allosaurus was one of the largest carnivorous dinosaurs of its time and was up to twelve feet long and weigh several tons.


The narrow head of this dinosaur adorned two large hump over the eyes. The overall quite large skull has, as usual, theropods, large openings, one of which produced some by air-filled cavities (such as expansion of the sinuses ). Thus it does not consists of a solid bone and was therefore much easier.

The neck was very strong and extremely agile. The animal moved away only on its hind legs. The relatively short arms were very strong and ended in a three-finger hand with sharp claws. The hind legs were long, the Allosaurus was a toe-walker like all theropods. A long tail balanced the body on its hind legs.

Way of life

The theses about the lifestyle of Allosaurus differ. See few paleontologists in Allosaurus fragilis a successful scavengers, others facing a hunter who could kill in groups and large sauropods. The lightweight design with powerful hind legs speaks rather for a hunter. This is also supported by studies of the skull, after which it is designed for very high loads. Such stress does not occur in the pure chewing a cadaver, but probably in the hunt for a live animal. Indicated the possibility of gregarious hunting behavior in groups, there is the one by finds of several animals in a reference (eg in the Cleveland -Lloyd Quarry ) and by finds of footprints of several large theropods, which apparently ran together. However, both are no confirmed evidence of group behavior, as well as let the skeletal accumulations otherwise explain the traces and securely Allosaurus can not be assigned.

Reproduction and Development

According to a group of U.S. researchers were some particularly large dinosaurs such as Allosaurus, able to reproduce already at an age of ten years. This behavior is an evolutionary advantage compared to those species that reproduce only in adult age. Could be demonstrated this knowledge by means of the bone finds. The bones showed already in young specimens on a striking for fertility fabric structure, which is necessary for continuously and readily available calcium reserves for the production of egg shells. The same structure is in living descendants today, for example, known birds.

The most well-known large Allosaurus specimens are estimated at an age of 13-19 years. This estimate is based on studies of Ellen, femur, tibia and humerus of the respective specimens. The maximum age of the species probably was 22-28 years, which is comparable to that of other large theropods. At the age of 15 years, the growth was most likely the most rapid. It is believed that during this time rose Allosaurus 148 kg per year.


Allosaurus lived at the same time as Stegosaurus, Brachiosaurus and Diplodocus in the Morrison Formation in North America. The Morrison Formation represents a rather open and dry habitats with large rivers, flood plains and small lakes. Food competitors of Allosaurus were probably also occurring in this formation, great theropods Torvosaurus and Ceratosaurus. Smaller theropods of the Morrison Formation, such as Ornitholestes or Coelurus other hand, competed with more than young animals and belonged in adult Allosauriern more on the menu.


Allosaurus fragilis was 9.1 meters long on average and about 1.7 tons. However, there are also some fragmentary findings that suggest that individual animals could be considerably larger. There are also remains of a very large Allosauriden called Allosaurus maximus maximus or Saurophaganax with an estimated length of up to about 13 meters. Two of the most famous specimens of Allosaurus are Big Al and Big - Al 2 that have been found by paleontologists in the United States and in the BBC documentary The Story of Big Al ( The Ballad of Big Al ) were shown.

Skull of Allosaurus fragilis

Allosaurus reconstruction in Dino park in Fürth ( Bayern)