Megalosaurus

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Megalosaurus Fossil range: Middle Jurassic
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Sauropsida Superorder: Dinosauria Order: Saurischia Suborder: Theropoda Family: Megalosauridae Genus: Megalosaurus Buckland, 1824
Species
M. bucklandii Mantell, 1827 (type) M. hesperis Waldmann, 1974  ?M. cambrensis (Newton, 1899) = Zanclodon cambrensis

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).

[edit] Discovery

The cover of Robert Plot's Natural History of Oxfordshire, 1677 (right). Plot's illustration of the lower extremity of a Megalosaurus femur (left).

Megalosaurus was the first dinosaur to be described. Part of a bone was recovered from a limestone quarry at Cornwell near Chipping Norton, Oxfordshire, 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.^[1]

The Cornwell bone was described again by Richard Brookes in 1763. He named it 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 subsequent 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".^[2]

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.^[3] In 1826, Ferdinand von Ritgen gave this dinosaur a complete binomial, Megalosaurus conybeari, which was not used by later authors and is now considered a nomen oblitum. 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.^[4] It would not be until 1842 that Richard Owen coined the term 'dinosaur'.

Engraving from William Buckland's "Notice on the Megalosaurus or great Fossil Lizard of Stonesfield", 1824. Caption reads "anterior extremity of the right lower jaw of the Megalosaurus from Stonesfield near Oxford".

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.

[edit] Description

Since those first finds, many other Megalosaurus bones have been recovered but still no complete skeleton has been found. Therefore, the details of Megalosaurus's physical appearance cannot be certain.

[edit] Early reconstructions

Reconstruction of Megalosaurus and Pterodactylus by Samuel Griswold Goodrich from 1859. This is typical of early reconstructions in presenting Megalosaurus as a quadruped; modern reconstructions make it bipedal.

In 1852, Benjamin Waterhouse Hawkins was commissioned to a build a model of Megalosaurus for the exhibition of dinosaurs at the Crystal Palace, which is still there to this day. 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.

[edit] Modern reconstructions

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 meters 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.

[edit] Inaccurate attributions

At one time, Megalosaurus was a 'wastebasket genus', used to classify many different kinds of large theropods. Dilophosaurus [1], Eustreptospondylus [2], and Metriacanthosaurus [3] 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.

[edit] In Popular Media

Outdated reconstruction in Crystal Palace, London.

Megalosaurus has the distinction of being the first dinosaur to appear in any popular media. Charles Dickens's novel Bleak House begins with a description of fog, whose primordial character is emphasized by mention of Megalosaurus. It has made a variety of other appearances as well. A Megalosaurus was one of the main dinosaurs featured in John Brosnan's 1984 novel, Carnosaur though it was not featured in its film adaptation. In the TV Show Dinosaurs, Earl Sinclair, the father, is a Megalosaurus. It also appears in the Doctor Who book, "The Last Dodo" by Jacqueline Rayner.

[edit] References

[edit] Gallery

Megalosaurus - 19th Century reconstruction	Megalosaurus right tibia (& left metatarsals) Oxford University Museum of Natural History	The Megalosaurus display at OU Museum of Natural History	Megalosaurus vertebra - OUMNH
Megalosaurus foot prints reconstructed on OUMNH lawn

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