Megalosaurus (meaning "great lizard", from Greek μέγας, megas, meaning 'big', 'tall' or 'great' and σαῦρος, sauros, meaning 'lizard') is an extinct genus of large meat-eating theropod dinosaurs of the Middle Jurassic period (Bathonian stage, 166 million years ago) of Southern England. Although fossils from other areas have been assigned to the genus, the only certain remains of Megalosaurus come from Oxfordshire and date to the late Middle Jurassic.
Megalosaurus was, in 1824, the first genus of non-avian dinosaur to be validly named. The type species is Megalosaurus bucklandii, named in 1827. In 1842, Megalosaurus was one of three genera on which Richard Owen based his Dinosauria. On Owen's directions a model was made as one of the Crystal Palace Dinosaurs, which greatly increased the public interest for prehistoric reptiles. Subsequently, over fifty other species would be classified under the genus, originally because dinosaurs were not well known, but even during the 20th century after many dinosaurs had been discovered. Today it is understood these additional species were not directly related to M. bucklandii, which is the only true Megalosaurus species. Because a complete skeleton of it has never been found, much is still unclear about its build.
The first naturalists who investigated Megalosaurus mistook it for a gigantic lizard of 20 metres (66 ft) length. In 1842, Owen concluded that it was no longer than 9 metres (30 ft), standing on upright legs. He still thought it was a quadruped, though. Modern scientists, by comparing Megalosaurus with its direct relatives in the Megalosauridae, were able to obtain a more accurate picture. Megalosaurus was about 6 metres (20 ft), weighing about 700 kilograms (1,500 lb). It was bipedal, walking on stout hindlimbs, its horizontal torso balanced by a horizontal tail. Its forelimbs were short, though very robust. Megalosaurus had a rather large head, equipped with long curved teeth. It was generally a robust and heavily muscled animal.
