Artwork showing the relative scale of humans and Allosaurus (meaning 'different lizard'). This large theropod, an apex predator, lived during the Late Jurassic period and is often referred to as the 'lion of the Jurassic'. It averaged 8.5 m (28 ft) long but some specimens may have grown to lengths of 9.7 m (32 ft). It was therefore a fair bit smaller than Tyrannosaurus (which lived 80 million years later) but was no doubt still a formidable animal.