Allosaurus jimmadseni

Allosaurus jimmadseni is one of two different Allosaurus species found in the monument.

NPS Photo/Bob Walters Tess Kissinger

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Allosaurus jimmadseni is the second species of Allosaurus found at Dinosaur National Monument. The first specimen of A. jimmadseni was found in the monument. It is much rarer than Allosaurus fragilis and they differ in their skeletal details.

Allosaurus, meaning "different reptile," is a theropod (meat eating dinosaur) that probably ate other smaller dinosaurs. Its teeth were serrated like steak knives for cutting flesh. Adults hunted by overpowering their prey, possibly in small groups. Juvenile Allosaurus relied on their longer limb bones that were better adapted to running in order to hunt small vertebrates. Allosaurus was not the largest predator of the time, but its sharp teeth and hook-shaped claws made Allosaurus a nightmare for many creatures of the Jurassic.

Only half of an Allosaurus jimmadseni skull has been found so far. However, the skull separated along its natural midline. Although only the left half of the skull is preserved, it shows both the outside shape and the internal structures, which are rarely seen. The entire braincase is present as well as both ear bones. For the first time in any Allosaurus the wishbone is in place. This Allosaurus jimmadseni is most complete Allosaurus of any species ever found.