Allosaurus was a large predatory bipedal dinosaur that lived during the late Jurassic period, roughly 155 to 145 million years ago. A. fragilis was the first species discovered, described by Orthniel Charles Marsh in 1877.
Some of these dinosaurs were taken from their epoch during the Noah's Ark Plan. However, when the systems that were to keep them in their confinement went corrupt, the Allosaurs escaped with the other dinosaurs and thrived in the surrounding areas.
Regina first encounters an Allosaurus in her way to search for a flamethrower. The Allosaurus tossed a jeep before it hunted her down. Another pair of Allosaurus was fought by Dylan and Regina once they escaped the Volcano. They used mounted cannons to drive off the Allosaurus before they proceeded further.