Allosaurus fragilis

Allosaurus is the best known large predatory dinosaur from the Late Jurassic of western North America, about 150 million years ago. Allosaurus fragilis is one of two well-attested species of Allosaurus, and there appears to be a time gradient between A. fragilis and A. jimmadseni. A. fragilis appears to have had a somewhat more robust skull, with a deeper back part of the skull where jaw-closing muscles were housed. It also had triangular horns above each of its eyes, as well as two small, bony ridges running down the top of the snout. Between mass-kill sites and trackways there is evidence that Allosaurus hunted in groups at least some of the time, which would be a terrifying thing to witness.