Megalosaurus (meaning "great lizard", from Greek μέγας, megas, meaning 'big', 'tall' or 'great' and σαῦρος, sauros, meaning 'lizard') is an extinct genus of large carnivorous theropod dinosaurs that lived during the Middle Jurassic (Bathonian age, ~166 million years ago) in what is now 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. The earliest remains of Megalosaurus were described in the 17th century, and were initially interpreted as the remains of elephants or giants. Megalosaurus was named in 1824 by William Buckland, becoming the first genus of dinosaur to be validly named (other than birds, not then recognized as dinosaurs). The type species is M. bucklandii, named in 1827 by Gideon Mantell, after Buckland. In 1842, Megalosaurus was one of three genera on which Richard Owen based his Dinosauria, along with Iguanodon and Hylaeosaurus. On Owen's directions a model was made as one of the Crystal Palace Dinosaurs, which greatly increased the public interest for prehistoric reptiles. Over 50 other species would eventually be classified under the genus; at first, this was because so few types of dinosaur had been identified, but the practice continued even into the 20th century after many other dinosaurs had been discovered. Today it is understood that none of these additional species was 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 quadrupedal lizard 20 metres (66 ft) in length. In 1842, Owen concluded that it was no longer than 9 metres (30 ft). Modern scientists were able to obtain a more accurate picture, by comparing Megalosaurus with its direct relatives in the Megalosauridae. Megalosaurus was about 6 metres (20 ft) long, 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. At the time Megalosaurus lived, Europe formed an island archipelago bounded by then narrow Atlantic Ocean and Tethys Ocean, with Megalosaurus inhabiting an island formed by the London–Brabant Massif, where it likely served as the apex predator of its ecosystem, coexisting with other dinosaurs like the large sauropod Cetiosaurus, stegosaurs, ankylosaurs, and heterodontosaurids.
Discovery and naming
Edward Lhuyd's tooth (specimen OU 1328)
In 1699, Edward Lhuyd described what he believed to have been a fish tooth (called Plectronites), later believed to be part of a belemnite, that was illustrated alongside the holotype tooth of the sauropod "Rutellum impicatum" along with another tooth from a theropod. Later studies found that the theropod tooth, known as specimen 1328 (University of Oxford coll. #1328; lost?) almost certainly was a tooth crown that belonged to an unknown species of Megalosaurus. OU 1328 has since been lost and it was not confidently assigned to Megalosaurus until the tooth was re-described by Delair & Sarjeant (2002). OU 1328 was collected near Caswell, near Witney, Oxfordshire sometime during the 17th century and became the third dinosaur fossil to ever be illustrated, after "Scrotum humanum" in 1677 and "Rutellum impicatum" in 1699.
"Scrotum humanum" Megalosaurus may have been the first non-avian dinosaur to be described in the scientific literature. The earliest possible fossil of the genus, from the Taynton Limestone Formation, was the lower part of a femur, discovered in the 17th century. Part of a bone was recovered from the Taynton Limestone Formation of Stonesfield limestone quarry, Oxfordshire in 1676. Sir Thomas Pennyson gave the fragment to naturalist Robert Plot, who published a description and illustration in his Natural History of Oxfordshire in 1676. It was the first illustration of a dinosaur bone published. Plot correctly identified the bone as the lower extremity of the thighbone or femur of a large animal and he recognized that it was too large to belong to any species known to be living in England. He therefore at first concluded it to be the thigh bone of a Roman war elephant and later that of a giant human, such as those mentioned in the Bible. The bone has since been lost, but the illustration is detailed enough that some have since identified it as that of Megalosaurus.
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