Megalosaurus

Megalosaurus was an extinct dinosaur. Its name means "great lizard," from the Greek words for "big" and "lizard." It was a large meat-eating dinosaur, called a theropod. It lived in what is now southern England during the Middle Jurassic period, about 166 million years ago. Fossils from other places have also been given the name Megalosaurus, but the only certain remains come from Oxfordshire and date to the late Middle Jurassic.

The first remains of Megalosaurus were described in the 1600s. People at the time thought they belonged to elephants or giants. William Buckland named the dinosaur in 1824, making it the first dinosaur genus to be validly named. Its main species, M. bucklandii, was named in 1827 by Gideon Mantell, after Buckland. In 1842, Richard Owen used Megalosaurus, along with Iguanodon and Hylaeosaurus, to help define Dinosauria. A model of Megalosaurus was made for the Crystal Palace Dinosaurs. This helped many people become interested in prehistoric reptiles. Over 50 other species were later placed in the genus. Today, scientists know that none of them was closely related to M. bucklandii, the only true Megalosaurus species.

The first scientists who studied Megalosaurus thought it was a huge four-legged lizard about 20 metres (66 ft) long. In 1842, Owen concluded that it was no longer than 9 metres (30 ft). Modern scientists compared it with its close relatives in the Megalosauridae and got a more accurate picture. Megalosaurus was about 6 metres (20 ft) long and weighed about 700 kilograms (1,500 lb). It walked on two legs, with strong hind legs, a horizontal body, and a balancing tail. Its front legs were short but very strong. It had a rather large head with long, curved teeth. It was a sturdy animal with heavy muscles.

When Megalosaurus lived, Europe was a group of islands separated by the narrow Atlantic Ocean and Tethys Ocean. Megalosaurus lived on an island formed by the London–Brabant Massif. It was likely the top predator of its ecosystem. It lived alongside other dinosaurs, such as the large sauropod Cetiosaurus, stegosaurs, ankylosaurs, and heterodontosaurids.

Discovery and naming

Bone pieces from a large, unknown animal were first found in Oxfordshire in the 1670s. Naturalist Robert Plot drew one of them. At first he thought it came from a Roman war elephant or a giant human. In the early 1800s, more bones and a lower jaw were found at the Stonesfield Slate mine. Geologist William Buckland studied them. French scientist Georges Cuvier realized they came from a giant creature that looked like a lizard. In 1824, Buckland officially announced the name Megalosaurus to the Geological Society of London. The name comes from the Greek word megas, which means "large." Later, Gideon Mantell gave the species its name, Megalosaurus bucklandii. In 1841, Richard Owen placed Megalosaurus in a new group called the Dinosauria, along with two other large reptiles. In 1852, a life-sized model of the animal was built for the exhibition of prehistoric animals at the Crystal Palace Park. It still stands there today.

Scientists have kept studying Megalosaurus bones, especially those from the Stonesfield quarries, which were worked until 1911. Most of these fossils are single bones from the pelvis and hindlimbs. In 1997, a group of fossilized footprints was found at Ardley, near Oxford. Some were thought to have been made by Megalosaurus, but this is hard to prove. In 2024, more tracks were found at a quarry in Bicester.

Description

Many more Megalosaurus bones have been found since the first discoveries. However, no complete skeleton has been found yet, so scientists are not completely sure what it looked like. A full osteology of all known material was published in 2010 by Benson. For a long time, books based on Owen's 1841 estimate said it was about nine meters (30 feet) long. In 1984, David Bruce Norman thought it was seven to eight meters long. In 2010, Paul estimated it was six meters long and weighed 700 kilograms. Benson said it was still one of the largest Middle Jurassic theropods, even though it was medium-sized. Overall, it had the typical body of a large carnivore. It walked on two legs and had a long tail to help balance its body. Its skull is poorly known, and the praemaxilla is not known at all. Its teeth were long and pointed like daggers, and they were used to cut the flesh of its prey. The antorbital fenestra, jugal bone, air sac, and nasal bone are all linked to its skull. The jugal may have a special feature that is unique to Megalosaurus, called an autapomorphy. The lower jaw, or mandibula, was narrow. In some ways it looked like the jaw of Piatnitzkysaurus. The surangular did not have a bony shelf.

The vertebral column was probably made up of 10 neck bones, 13 back bones, five hip bones, and 50 to 60 tail bones. This is common for basal Tetanurae. Many of the vertebrae had large pleurocoels. Some were opisthocoelous, or had a hyposphene–hypantrum complex. The scapula was short and wide. The scapulocoracoid had no visible suture, but it did have a large foramen. The humerus was very strong. It had a large deltopectoral crest for the Musculus pectoralis major and Musculus deltoideus. The ulna was also very strong, with a large olecranon for the Musculus triceps brachii. The Radius, wrist, and hand are unknown. The ilium was long and low. The thigh bone had a wide greater trochanter and a strong lesser trochanter. Its condyles were separated by a groove at the front. The shinbone was fairly straight. The astragalus covered part of the shinbone. Only three metatarsals are known.

For decades, Megalosaurus was used as a name for many large meat-eating dinosaurs. Later, researchers such as Ronan Allain suggested that some of these fossils belonged to different species. In 2008, Benson and colleagues found several autapomorphies in the lower jaw. These features set Megalosaurus apart from its relatives. Benson also concluded that the simplest explanation, the most parsimonious one, is that the Stonesfield Slate material comes from a single species.

Phylogeny

In 1824, Buckland placed Megalosaurus among the Sauria. He thought this group was more closely related to modern lizards than to crocodiles. In 1842, Owen made Megalosaurus one of the first three genera placed in the Dinosauria. In 1850, Prince Charles Lucien Bonaparte created a separate family, Megalosauridae, with Megalosaurus as the type genus. For a long time, scientists were not sure how Megalosaurus was related to other dinosaurs. It was seen as a "primitive" member of the Carnosauria, a group that many large meat-eating dinosaurs belonged to.

In the late 20th century, a new method called cladistics made it possible for the first time to measure how closely different groups were related. In 2012, Matthew Carrano et al. showed that Megalosaurus was the sister species of Torvosaurus within the Megalosaurinae.

Paleobiology

Megalosaurus lived in what is now Europe during the Bathonian stage of the Middle Jurassic, about 166 to 168 million years ago. Old pictures from the 1800s and early 1900s often showed Megalosaurus hunting Iguanodon, another of the first dinosaurs to be named. We now know these pictures are not accurate, because Iguanodon skeletons are found in much younger Cretaceous rocks. The only certain Megalosaurus bucklandii remains come from the early and middle Bathonian of Oxfordshire and Gloucestershire, in England. Other dinosaurs from the Bathonian of Britain include the large meat-eater Cruxicheiros, the uncertain Iliosuchus, the small tyrannosaur relative Proceratosaurus, and the long-necked plant-eaters Cardiodon and Cetiosaurus. Megalosaurus may have hunted stegosaurs and sauropods.

In 2010, Benson concluded from its size and how often its remains are found that Megalosaurus was the apex predator of its habitat. He noted that Cetiosaurus was missing from the French Armorican Massif. This suggested that Megalosaurus lived only on the London-Brabant Massif, an island that included parts of southern Britain and nearby areas of France, the Netherlands, Belgium, and Germany. Scientists have asked why the island's dinosaurs did not become smaller over time, as often happens on islands of this size. One possible reason is that the island stayed connected to larger lands, such as the Fennoscandian Shield and the area now under the North Sea, through shallow water. Plants from the Taynton Limestone Formation, where many Megalosaurus fossils are found, were mostly conifers and other ancient plant groups. This suggests a dry coast with mangroves.

Paleopathology

A Megalosaurus rib shown in 1856 and 1884 by Sir Richard Owen has a swollen spot near its base. The swelling appears to have been caused by a fracture that had healed, at the point where the rib would have joined its backbone.

Species and synonyms

In the later 1800s, Megalosaurus was seen as the typical meat-eating dinosaur. When scientists found remains that did not seem different enough to need their own genus, often just single teeth, they were placed under Megalosaurus. This made it a wastebasket taxon, a kind of default genus. Over time, Megalosaurus held more species than any other non-bird dinosaur genus, though many of these names were not very useful. In the 1900s, scientists slowly stopped this practice. Even so, when they found meat-eating dinosaurs that older books had wrongly placed in another group, they often still chose Megalosaurus as the name.

Many species were named under Megalosaurus over the years. Many were later moved to other genera, and some were found to be uncertain. A few were based on just one tooth or bone, and some were later found to belong to very different animals. The history of these names is shown in the tables below.