Megalosaurus (meaning "Great Lizard", from Greek, μεγαλο-/megalo- meaning 'big', 'tall' or 'great' and σαυρος/sauros meaning 'lizard') is a genus of large meat-eating theropod dinosaurs of the Middle Jurassic Period (Bathonian) of Europe (Southern England, France, Portugal).
Megalosaurus was the first dinosaur to be described. Part of a bone was recovered from a limestone quarry at Cornwell near Oxford, England in 1676. The fragment was sent to Robert Plot, Professor of Chemistry at the University of Oxford and first curator of the Ashmolean Museum, who published a description in his Natural History of Oxfordshire in 1677. He correctly identified the bone as the lower extremity of the femur of a large animal and he recognized that it was too large to belong to any known species; he considered it to be the thigh bone of a giant. The bone has since been lost but the illustration is detailed enough to identify it clearly as the femur of a Megalosaurus.
The Cornwell bone was described again by Richard Brookes in 1763. He named it (perhaps inadvertently) Scrotum humanum, while describing its similar appearance to a pair of human testicles. The label was not considered to be a "name" for the animal in question at the time, and was not used in subsequnt literature. Technically, the name was published after the advent of binomial nomenclature, and although this name theoretically had priority over Megalosaurus, the rules of the ICZN state that if a name falls into disuse for 50 years after publication, it is no longer in competition for priority. Therefore, the name Scrotum humanum is a nomen oblitum, or "forgotten name".
More discoveries were made, starting in 1815, again at the Stonesfield quarry. They were acquired by William Buckland, Professor of Geology at the University of Oxford and dean of Christ Church. He did not know to what animal the bones belonged but, in 1818, after the Napoleonic Wars, the French comparative anatomist Georges Cuvier visited Buckland in Oxford and realised that the bones belonged to a giant lizard-like creature. Buckland then published descriptions of the bones in Transactions of the Geological Society, in 1824 (Physician James Parkinson had described them in an article in 1822).
By 1824, Buckland had a piece of a lower jaw with teeth, some vertebrae, and fragments of pelvis, scapula and hind limbs, probably not all from the same individual. Buckland identified the organism as being a giant animal related to the Sauria (lizards) and he placed it in the new genus Megalosaurus, estimating the animal to be 12 m long in life. In 1826, Ferdinand Ritgen gave this dinosaur a complete binomial, Megalosaurus conybeari, which was not used by later authors and is now ocnsidered a nomen oblitum ("forgotten name"). A year later, in 1827, Gideon Mantell included Megalosaurus in his geological survey of southeastern England, and assigned the species its current binomial name, Megalosaurus bucklandii. It would not be until 1842 that Richard Owen coined the term 'dinosaur'.
In 1997, a famous group of fossilised footprints (ichnites) was found in a limestone quarry at Ardley, 20 km Northeast of Oxford, England. They were thought to have been made by Megalosaurus and possibly also some left by Cetiosaurus. There are replicas of some of these footprints, set across the lawn of Oxford University Museum of Natural History.
Since those first finds, many other Megalosaurus bones have been recovered but still no complete skeleton has been found. Therefore, we cannot be certain about the details of Megalosaurus's physical appearance.
Early paleontologists, never having seen such a creature before, reconstructed it like the dragons of popular mythology, with a huge head and walking on all fours. It was not until the middle of the nineteenth century, when other theropods began to be discovered in North America, that a more accurate picture was developed. Some confusion still exists, for at one time (before classification of dinosaurs became the serious business it is today), all theropods from Europe were given the title Megalosaurus. Since then, these have mostly been reclassified but older papers can still cause confusion. For further confusion, the most reproduced anatomy diagram of a Megalosaurus' skeleton was produced before any vertebrae had been recovered. While drawing it, Friedrich von Huene of the University of Tübingen, Germany, instead used the backbones of Altispinax, a mysterious big theropod known from high-spined dorsal vertebrae and at times classified as a spinosaur. Hence, many later drawings, based on his original, show Megalosaurus with a deep spinal ridge or even a small sail, like that of Spinosaurus.
In fact, Megalosaurus did have a relatively large head and the teeth were clearly that of a carnivore. However, the long tail would have balanced the body and head and so Megalosaurus is now restored as a bipedal beast—like all other theropods—about nine metres in length. The structure of the cervical vertebrae suggests that its neck would have been very flexible. To support its weight of around one tonne, the legs were large and muscular. Like all theropods, it had three forward facing toes and a single reversed one. Although they had not reached the minuscule size of later theropods like Tyrannosaurus, the fore limbs of Megalosaurus were small and probably had three or four digits.
Living in what is now Europe, during the Jurassic Period (181 to 169 million years ago), Megalosaurus may have hunted stegosaurs and sauropods. Repeated descriptions of Megalosaurus hunting Iguanodon (another of the earliest dinosaurs named) through the forests that then covered the continent are probably inaccurate, because Iguanodon skeletons are found in much younger Early Cretaceous formations. No fossils assignable to Megalosaurus have been discovered in Africa, contrary to some outdated dinosaur books.
Although Megalosaurus was a powerful carnivore and could probably have attacked even the largest sauropods, it is also likely that it gained some of its food by scavenging. That is not to detract from its prowess as a hunter (Tyrannosaurus probably did much the same). Efficiency was necessary to feed such a large body.
There is a good descriptive display of Megalosaurus and of the history of discovery, in the Oxford University Museum of Natural History.
At one time, Megalosaurus was a 'wastebasket' genus, used to classify many different kinds of large theropods. Dilophosaurus , Eustreptospondylus , and Metriacanthosaurus  were all initially believed to be species of Megalosaurus. In recent years, the genus has been subject to extensive reconsideration and most of the extraneous species have been removed.
In Popular Media
In the TV Show Dinosaurs (TV series), Earl Sinclair, the father, is a Megalosaurus.
- Halstead, L.B. (1970). "Scrotum humanum Brookes 1763 - the first named dinosaur." Journal of Insignificant Research, 5: 14-15.
- Buckland, W. (1824). "Notice on the Megalosaurus or great Fossil Lizard of Stonesfield." Transactions of the Geological Society of London, series 2, vol. 1: 390–396.
- Mantell, G. (1827). "Illustrations of the geology of Sussex: a general view of the geological relations of the southeastern part of England, with figures and descriptions of the fossils of Tilgate Forest."