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WVGES Museum of Geology & Natural History,

Dinosaurs: Allosaurus


Allosaurus fragilis

Allosaurus was a formidable predator that walked on two powerful legs, had a strong S-shaped neck, and vertebrae different from those of other dinosaurs (hence its name, the ''different lizard''). It had a massive tail, a bulky body, and heavy bones. Its arms were short and had three-fingered hands with sharp claws as long as 6 inches.
Allosaurus skull image This is a life-size replica of an Allosaurus skull and lower jaws found in the Morrison Formation of the Cleveland-Lloyd Quarry in Central Utah, Jurassic age: 130 to 156 million years ago. (33 inches long, 18 inches high, and 12 inches wide. Photo: E. Ray Garton)
Allosaurus was up to 38 feet long and 16.5 feet tall. It had a 3-foot long skull with two short brow-horns and bony knobs and ridges above its eyes and on the top of the head. It had large, powerful jaws with long, sharp serrated teeth that were 2 to 4 inches long.
Gastralia (hanging belly ribs) are thin, fragile ribs that helped support and protect the internal organs (like the lungs) in the middle area of the body. These ribs were not attached to the backbone; they were attached to the skin in the belly area.
Allosaurus fragilis Fleshed-out juvenile Allosaurus fragilis dinosaur model from the Morrison Formation (Jurassic Period) of central Utah, housed at the WVGES Museum and affectionately known as Al (Photo: John M. Bocan)
The different species of Allosaurus varied in weight. Allosaurus fragilis, A. atrox, and A. ferox weighed about 1.1 to 1.9 tons. A. amplexus was much heavier and weighed about 2.7 to 5.5 tons. Allosaurus was the top predator of the Jurassic.
Museum Curator: E. Ray Garton:
Page last revised January 20, 2022.
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