Iguanodon: Gideon Mantell and the Discovery of the Sussex Teeth

Iguanodon was one of the first dinosaurs known to science. Its story began in 1822 in Sussex, in south-east England, when the country doctor Gideon Mantell and his wife Mary Ann collected strange, worn fossil teeth from quarries in Tilgate Forest. In 1825 Mantell named the animal Iguanodon, “iguana tooth”, the second dinosaur ever named and the first identified as a giant plant-eating reptile.

Background: a doctor with a passion for fossils

Gideon Mantell was born in Lewes, Sussex, in 1790, the son of a shoemaker. He trained as a surgeon and built a busy medical practice, but his great passion was geology. He collected fossils from the chalk and sandstones of the Weald, the area of south-east England between the North and South Downs.

In 1816 he married Mary Ann Woodhouse, who shared his interest and drew many of the illustrations for his first major book, The Fossils of the South Downs, published in 1822. At the time, geology was a new and exciting science, and its leaders in London and Oxford were mostly wealthy gentlemen or clergymen. Mantell, a provincial doctor, was eager to win their respect.

The discovery of the teeth

The famous story, told later by Mantell himself, is that in 1822 Mary Ann found a large fossil tooth in a heap of roadside stones while her husband was visiting a patient near Cuckfield. The stones came from quarries in Tilgate Forest, in rocks now known to belong to the Wealden Group of the Early Cretaceous, roughly 140 to 130 million years old.

Historians, notably Dennis Dean, have questioned this account. Mantell had already obtained fossils from the Cuckfield quarrymen, and some of the teeth may have reached him that way. What is clear is that by 1822 the Mantells had several unusual teeth, ridged and worn flat as if they had ground up tough plants.

Doubt from the experts

Mantell showed the teeth to leading scientists. In 1823 the geologist Charles Lyell took one to Paris, where Georges Cuvier, the greatest anatomist of the day, at first suggested it came from a rhinoceros. William Buckland in Oxford also doubted that the teeth belonged to a giant reptile and thought they were probably from fish or mammals, and possibly from younger rocks.

The breakthrough came in 1824 at the Hunterian Museum in London. Samuel Stutchbury, an assistant there, noticed that the fossil teeth resembled those of a modern iguana, though they were many times larger. Cuvier soon revised his opinion and accepted that the teeth came from an unknown plant-eating reptile.

Naming Iguanodon in 1825

Mantell’s paper “Notice on the Iguanodon, a newly discovered fossil reptile, from the sandstone of Tilgate Forest, in Sussex” was read to the Royal Society on 10 February 1825 and published in its Philosophical Transactions. He had considered calling the animal “Iguanasaurus”, but William Conybeare suggested the name Iguanodon.

Scaling up from an iguana, Mantell estimated a length of around 60 feet (18 metres), a figure he later reduced. The paper helped Mantell become a Fellow of the Royal Society that same year. By then, Buckland had already named Megalosaurus in 1824, so Iguanodon became the second of these giant extinct reptiles to be named.

The Maidstone specimen and early reconstructions

In 1834 quarrymen at Maidstone in Kent uncovered a block containing a partial skeleton. Mantell’s friends bought it for him for £25. Nicknamed the “Mantel-piece”, it gave him far more of the skeleton to work with. The town of Maidstone later added an Iguanodon to its coat of arms.

From these remains Mantell pictured Iguanodon as a huge, lizard-like animal walking on all fours, with a cone-shaped bone, actually a thumb spike, placed on its nose like a horn. In 1842 Richard Owen grouped Iguanodon, Megalosaurus and Mantell’s Hylaeosaurus in a new group he called Dinosauria, “terrible lizards”. Owen’s version of Iguanodon, a bulky, rhinoceros-like quadruped, was built as a life-size sculpture for the Crystal Palace dinosaurs in 1854.

The picture changed dramatically after 1878, when miners at Bernissart in Belgium found dozens of complete Iguanodon skeletons. Studied by Louis Dollo, the Bernissart Iguanodons revealed the true position of the thumb spike.

Mantell’s later life

Mantell’s fame did not bring him security. His medical practice suffered as he devoted himself to geology, and in 1838 he sold his collection to the British Museum for £4,000. Mary Ann left him around 1839. In 1841 he was badly injured in a carriage accident, which left him with lasting spinal pain.

He also became locked in a bitter rivalry with Richard Owen, who he felt took credit for his work. Mantell died in London on 10 November 1852 after an overdose of opium, which he had taken for pain.

What Iguanodon was really like

Modern research presents a very different animal from Mantell’s giant iguana. Iguanodon bernissartensis, the best-known species, lived in Europe about 126 to 122 million years ago, during the Early Cretaceous. Adults reached roughly 10 metres in length and probably weighed around three to four tonnes, although estimates vary.

Iguanodon belonged to the ornithopods, a group of plant-eating dinosaurs that later included the duck-billed hadrosaurs. It had a toothless beak at the front of its jaws and rows of grinding cheek teeth behind, well suited to chewing ferns, horsetails and conifers. Its strong arms ended in hands with three central fingers that could bear weight, a flexible fifth finger for grasping and the famous conical thumb spike, perhaps used for defence or for handling food.

For much of the 20th century Iguanodon was shown standing upright like a kangaroo, propped on its tail. Since the 1980s, studies of its skeleton have suggested that adults usually walked on all fours with the back roughly horizontal, rising onto the hind legs at times. Younger, lighter animals may have moved on two legs more often.

Key people

• Gideon Mantell (1790–1852): Sussex surgeon and geologist who named Iguanodon and Hylaeosaurus.
• Mary Ann Mantell: his wife, a skilled illustrator, credited by Mantell with finding the first tooth.
• William Buckland: Oxford geologist who named Megalosaurus and at first doubted Mantell.
• Georges Cuvier: French anatomist whose change of mind helped Mantell’s case.
• Richard Owen: anatomist who coined the word dinosaur in 1842 and became Mantell’s rival.

Myths and facts

• “Mary Ann found the first tooth on a roadside”: this is Mantell’s own later version of events, and it may be simplified. Some teeth may have come from quarrymen.
• “Iguanodon had a horn on its nose”: this was an early mistake. The cone-shaped bone was a thumb spike.
• “Mantell’s teeth define Iguanodon”: in 2000 the official type species of the genus was changed to the Belgian Iguanodon bernissartensis, because Mantell’s teeth were not distinctive enough to define a species.

Timeline

• 1790: Gideon Mantell is born in Lewes, Sussex.
• 1822: The Mantells obtain the first Iguanodon teeth; The Fossils of the South Downs is published.
• 1823: Cuvier, shown a tooth, at first suggests it belongs to a rhinoceros.
• 1824: Samuel Stutchbury notes the resemblance to iguana teeth.
• 1825, 10 February: Mantell’s paper naming Iguanodon is read to the Royal Society.
• 1834: The partial skeleton known as the Mantel-piece is found at Maidstone.
• 1842: Richard Owen names the Dinosauria, including Iguanodon.
• 1852, 10 November: Mantell dies in London.

Why it matters

Iguanodon showed that giant reptiles had once grazed on land, not just swum in ancient seas. Together with Megalosaurus, it laid the foundations for the idea of dinosaurs, and Mantell’s struggle to have his ideas accepted shows how science advanced through evidence, argument and revision.