Megalosaurus

Megalosaurus was a genus of large meat-eating dinosaurs of the Jurassic period.

Discovery

Megalosaurus was one of the first dinosaurs 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 identifed 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, who named it Scrotum humanum based on the similarity of appearance to a pair of human testicles. (Although this name theoretically has priority, subsequent authors have chosen to treat it as a joke rather than a serious attempt to propose a scientific name, or possibly not compliant with binomial nomenclature but rather with the old, descriptive approach).

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

More discoveries were made starting in 1815, this time at the Stonesfield quarry north of Oxford, and they were acquired by William Buckland, Professor of Geology at the University of Oxford and dean of Christ Church.

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".

Physician James Parkinson described them in an article in 1822, and two years later Buckland published his own paper. By 1824, he 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 named the genus Megalosaurus, estimating it to be 40 feet (12 m) long. In 1826 Georges Cuvier gave this dinosaur its species name: Megalosaurus bucklandi ("Buckland's big lizard").

Description

Early reconstructions

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 been mostly reclassified but older papers are often the cause of confusion. For further confusion, the most reproduced anatomy diagram of Megalosaurus' skeleton was produced before any vertebrae had been recovered. While drawing it, Friedrich von Huene of the University of Tubingen, 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.

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, and 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, Megalosaurus' arms were small and probably had three or four fingers.

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.