Megalosaurus

Megalosaurus was an extinct dinosaur. Its name means "great lizard," coming from the Greek words for "big" and "lizard." It was a large meat-eating dinosaur, called a theropod, that 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, and 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, which greatly increased public interest in prehistoric reptiles. Over 50 other species were later placed in the genus, but today scientists understand 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, comparing it with its close relatives in the Megalosauridae, 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, and it was a sturdy, heavily muscled animal.

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, living alongside other dinosaurs such as the large sauropod Cetiosaurus, stegosaurs, ankylosaurs, and heterodontosaurids.

Discovery and naming

Bone fragments from a large, unknown animal were first found in Oxfordshire in the 1670s. Naturalist Robert Plot drew one of them and at first 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, and French scientist Georges Cuvier realized they came from a giant lizard-like creature. In 1824, Buckland formally announced the name Megalosaurus to the Geological Society of London. The name comes from the Greek word megas, meaning "large." Later, Gideon Mantell gave the species its name, Megalosaurus bucklandii. In 1841, Richard Owen grouped Megalosaurus with two other large reptiles into a new group called the Dinosauria. In 1852, a life-sized model of the animal was built for the exhibition of prehistoric animals at the Crystal Palace Park, where it still stands today.

Scientists have continued to study 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, though 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, but no complete skeleton has been found yet, so its exact appearance is not certain. A full osteology of all known material was published in 2010 by Benson. Traditionally, texts following Owen's 1841 estimate gave a body length of about nine meters (30 feet). In 1984, David Bruce Norman thought it was seven to eight meters long, while Paul in 2010 estimated six meters and 700 kilograms. Benson said it was still among the largest Middle Jurassic theropods, though it was medium-sized. In general, it had the typical build of a large carnivore, walking on two legs with a long tail to balance its body. Its skull is poorly known, and the praemaxilla is not known at all. Its teeth were long and dagger-like, used to slice the flesh of prey, and the antorbital fenestra, jugal bone, air sac, and nasal bone are all linked to its skull, with a possible autapomorphy in the jugal. The lower jaw, or mandibula, was narrow, and it resembled that of Piatnitzkysaurus in some ways, with the surangular lacking a bony shelf.

The vertebral column was probably divided into 10 neck, 13 back, five hip, and 50 to 60 tail vertebrae, as is common for basal Tetanurae. Many vertebrae had large pleurocoels, and some were opisthocoelous or had a hyposphene–hypantrum complex. The scapula was short and wide, and the scapulocoracoid had no visible suture, though it had a large foramen. The humerus was very robust, with a large deltopectoral crest for the Musculus pectoralis major and Musculus deltoideus. The ulna was extremely robust, with a large olecranon for the Musculus triceps brachii. The Radius, wrist, and hand are unknown. The ilium was long and low, and the thigh bone had a wide greater trochanter and a robust lesser trochanter. Its condyles were separated by a front groove, and the shinbone was relatively straight. The astragalus covered part of the shinbone, and only three metatarsals are known.

For decades, Megalosaurus was used as a catch-all 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 identified several autapomorphies in the lower jaw that set Megalosaurus apart from its relatives. Benson also concluded it was most parsimonious to assume that the Stonesfield Slate material represents a single species.

Phylogeny

In 1824, Buckland placed Megalosaurus among the Sauria, a group he thought 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, the exact relationships of Megalosaurus remained unclear. It was seen as a "primitive" member of the Carnosauria, the group that most large theropods were grouped into.

In the late 20th century, the new method of cladistics made it possible for the first time to calculate exactly how closely different groups were related to each other. 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. Descriptions from the nineteenth and early twentieth centuries often showed Megalosaurus hunting Iguanodon, another of the earliest named dinosaurs, through forests. We now know these pictures are inaccurate, 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 theropod Cruxicheiros, the uncertain Iliosuchus, the small tyrannosauroid Proceratosaurus, and the sauropods Cardiodon and Cetiosaurus. Megalosaurus may have hunted stegosaurs and sauropods.

In 2010, Benson concluded from its size and common presence that Megalosaurus was the apex predator of its habitat. He noted that Cetiosaurus was missing from the French Armorican Massif, which suggested that Megalosaurus was limited to the London-Brabant Massif, an island that included parts of southern Britain and nearby areas of France, the Netherlands, Belgium, and Germany. It has been 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, suggesting a seasonally 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 healed fracture, at the point where the rib would have joined its vertebra.

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. In time, Megalosaurus held more species than any other non-bird dinosaur genus, though most of these names were of doubtful value. In the 1900s, this practice was slowly stopped. Even so, scientists who found meat-eating dinosaurs that older books had wrongly placed in another group still often chose Megalosaurus as the default name when renaming them.

Over the years, many species were named under Megalosaurus, and many were later moved to other genera or found to be uncertain. A few were based on a single tooth or bone, and some were later found to belong to very different animals. The full history of these names is summarized in the tables below.