Deinonychus dinosaurs. Computer artwork of two Deinonychus dinosaurs. This small raptor reached about 3 metres in length and stood 1.5 metres tall. It was an agile predator that lived between 110 and 100 million years ago in the Cretaceous period. The large claws would have been lethal to its prey. Deinonychus had a large brain for its size and may have hunted in packs. Fossils of this dinosaur have been found in western North America.