Iguanodon

Family

Ornithischians

Era

Early Cretaceous, 135 million years ago

Where he lived?

Belgium, England, Germany, North Africa, and the USA

Weight

5.000Kg

Height

2,7m

Length

10m

Iguanodon is not the biggest or the fiercest dinosaur. It is something more unusual: one of the three animals behind the invention of the word “dinosaur”.

In 1842, British anatomist Richard Owen realised that three fossils described by that time, Megalosaurus, Hylaeosaurus and Iguanodon, shared features that did not fit any known reptile. He coined the term Dinosauria, meaning “terrible lizards”, for them. Before then, the word did not exist.

Its story also includes one of palaeontology’s most entertaining mistakes: for sixty years, Iguanodon was reconstructed with a horn on its nose that was actually a thumb.

Discovery and history

In 1822, English doctor and geologist Gideon Mantell described fossil teeth found in Sussex. They resembled those of a modern iguana, but were far larger. This inspired the name he published in 1825: Iguanodon, meaning “iguana tooth”.

Tradition says that his wife, Mary Ann Mantell, found the teeth while waiting for him to finish seeing a patient. The story is disputed, but it has been repeated so often that it has become part of the discovery’s history.

The decisive find came half a century later. In 1878, coal miners at Bernissart in Belgium came across a dinosaur graveyard 322 metres underground. Around 38 skeletons were recovered, many of them nearly complete, from what remains one of the most remarkable dinosaur sites ever excavated.

Palaeontologist Louis Dollo devoted much of his career to studying them. Thanks to these remains, Iguanodon went from an animal known through isolated teeth to one of the best-documented dinosaurs in the world. Several of those skeletons are still mounted in the museum in Brussels.

Physical characteristics

An adult Iguanodon measured about 10 metres long and stood 2.7 metres tall at the hips, with a weight of roughly 3 to 4.5 tonnes. It had a solid body, a flexible neck and a long, stiff tail that acted as a counterbalance.

The way it moved is particularly interesting. Iguanodon was a facultative quadruped: it usually walked on all fours with its hands on the ground, but could rise onto its hind legs to reach high branches, run or defend itself. Its forelimbs were almost as powerful as its hind limbs, which is unusual.

It had no front teeth. Instead, a horny beak cut through vegetation, while rows of continuously replacing teeth sat farther back. It also had structures similar to cheeks, which helped keep food inside its mouth while it processed it.

Diet and feeding

Iguanodon was strictly herbivorous. It ate ferns, cycads, conifers and low vegetation from the wet plains of Cretaceous Europe. Switching between two and four legs gave it access to plants near the ground as well as higher branches.

Its teeth were built to grind tough plant matter and were continually replaced as they wore down. Read more about large plant-eaters in what dinosaurs ate and 10 herbivorous dinosaurs.

Habitat and distribution

Iguanodon fossils occur in Lower Cretaceous formations across Western Europe: Belgium, England, Germany and Spain. It lived on river plains and in damp woodland, environments that favour fossilisation and help explain why its remains are so well preserved.

A clarification is needed because a great deal of outdated information is still repeated. For decades, remains from North America and North Africa were assigned to the genus. A review by David Norman between 2010 and 2012 showed that those fossils belonged to other animals. Today, Iguanodon is regarded as an exclusively European genus.

Spain has important sites containing iguanodontians, the wider group to which Iguanodon belongs, especially around Morella in Castellón. We cover them in which dinosaurs lived in Spain.

Behaviour and reproduction

The concentration of skeletons at Bernissart suggests that Iguanodons may have travelled in groups, although it is not firm proof: the bodies could also have been washed together. Herding would make sense for a large herbivore with no obvious offensive weapon apart from its thumb spike.

Like all dinosaurs, Iguanodon laid eggs, but little is known about its breeding behaviour.

Importance in palaeontology

Few animals have changed shape so many times in scientists’ reconstructions. Iguanodon has been imagined in turn as a giant four-legged lizard, an upright kangaroo-like animal propped on its tail and, finally, the facultative quadruped we reconstruct today.

That is exactly what it teaches us: palaeontology does not simply discover animals; it keeps correcting our picture of them. The full story appears in the origin of dinosaurs.

The horn that turned out to be a thumb

This is the best Iguanodon story, and it deserves to be told properly.

When Mantell reconstructed the animal from separate bones, he found a pointed, cone-shaped piece and did not know where to put it. With an iguana in mind, he made an understandable choice: he placed it on the snout like a rhinoceros horn.

That is how Iguanodon appeared in the Crystal Palace dinosaurs created in London in 1854, the first life-sized dinosaur sculptures ever made. They are still in the park, complete with horns on their noses.

There is a wonderful scene attached to them. On New Year’s Eve 1853, before the sculptures were finished, sculptor Benjamin Waterhouse Hawkins held a dinner for around twenty scientists inside the Iguanodon mould. They ate and raised their glasses while sitting inside the animal.

The mistake took sixty years to correct. The complete Bernissart skeletons found in 1878 made it clear that the bone did not belong on the head. It was the thumb.

One hand with three different jobs

The Iguanodon hand is one of the strangest designs of the Cretaceous, because its five fingers performed three different functions.

The thumb formed the famous spike: a solid, fixed cone that could not bend. It may have been used in defence, perhaps to strike a predator’s flank, or as a tool for breaking hard seeds and fruit.

The three middle fingers ended in hoof-like tips and supported the animal’s weight when it walked on all fours.

The fifth finger was long, flexible and able to grasp. It stood apart from the others and could curl around objects. One finger for gripping, three for walking and one for stabbing, all on the same hand.

How it chewed before true chewing existed

True chewing, grinding food with sideways movements, is something we normally associate with mammals. Reptile jaws usually move only up and down.

Iguanodon solved the problem differently. Its skull had flexible joints between the facial bones. When it closed its mouth, the upper jaws moved slightly outwards. This small shift rubbed the upper teeth against the lower teeth in a grinding action.

The mechanism is called pleurokinesis and helps explain the success of the ornithopods. It allowed them to process tough plants that other herbivores could not use as efficiently. Hadrosaurs, among the most abundant dinosaurs at the end of the Cretaceous, later emerged from this lineage.

The Iguanodon at Dinosaurland

The park has a life-sized Iguanodon, and it is one of the best models for understanding the true scale of these animals. Its teeth are not the impressive part; its sheer size is, especially for an animal that ate nothing but plants.

It is worth seeing alongside its relatives. Ouranosaurus was a closely related iguanodontian with a sail on its back, something Iguanodon did not have. Parasaurolophus and Tsintaosaurus were hadrosaurs, members of the lineage that followed and inherited this way of chewing. Triceratops represents the other major branch of the ornithischian dinosaurs.

You will find it on an outdoor trail among pine trees in Porto Cristo, Mallorca, together with more than 100 life-sized dinosaurs from around 40 species. Many are animatronic: they move and make sounds when you approach. Profiles of every species are available in the dinosaur section.

🎟️Come and see Iguanodon up close. Tickets are available at tickets.dinosaurland.es, with €1 off each ticket bought online. See tickets, prices and booking information for rates and conditions, and dates and opening times for opening days.

Have a young dinosaur fan at home? Download our printable PDF of Iguanodon to colour in.

Frequently asked questions about Iguanodon

What does Iguanodon mean?

“Iguana tooth.” Gideon Mantell gave it the name in 1825 because the fossil teeth found in Sussex resembled those of a modern iguana, although they were much larger.

Was Iguanodon the first dinosaur discovered?

It was the second dinosaur to receive a scientific name, in 1825, after Megalosaurus in 1824. It was also one of the three genera, alongside Megalosaurus and Hylaeosaurus, that Richard Owen used when he coined the word “Dinosauria” in 1842.

How big was Iguanodon?

Around 10 metres long and 2.7 metres tall at the hips, with a weight of between 3 and 4.5 tonnes.

Why did it have a spike on its thumb?

We do not know for certain. It may have served as a defence against predators or as a tool for breaking hard seeds and fruit. We do know that it was solid and fixed, so it could not bend.

Did scientists really put its thumb on its nose?

Yes. When the animal was reconstructed from isolated bones, the cone-shaped piece was interpreted as a nasal horn. That is how it appeared in the Crystal Palace dinosaurs sculpted in London in 1854. The mistake was corrected in 1878 after the complete Bernissart skeletons were found.

Did Iguanodon walk on two legs or four?

Both. It usually travelled on all fours but could rise onto its hind legs to reach high branches, run or defend itself. Old reconstructions showing it standing upright like a kangaroo and resting on its tail are incorrect.

What did Iguanodon eat?

Plants, including ferns, cycads, conifers and low vegetation. It cut them with a toothless horny beak and ground them with rows of continually replacing teeth. Cheek-like structures kept the food from falling out of the sides of its mouth.

Where have Iguanodon fossils been found?

In Western Europe: Belgium, England, Germany and Spain. The largest discovery came in 1878 at a coal mine in Bernissart, Belgium, where around 38 skeletons were found 322 metres underground.

Is Aladar from the film Dinosaur an Iguanodon?

Yes. The main character in Disney’s 2000 film is an Iguanodon, although the story takes major liberties: he lives alongside species from different periods and continents that never met in real life.

Can you see a life-sized Iguanodon in Mallorca?

Yes. It is at Dinosaurland in Porto Cristo, on an outdoor trail with more than 100 life-sized dinosaurs, many of them animatronic.

The dinosaur that taught us how to be wrong

For sixty years, everyone saw a horn where there was a thumb. It was not carelessness: given the bones on the table at the time, it was a reasonable conclusion.

What changed the story was not a better idea, but thirty-eight complete skeletons appearing three hundred metres below ground in a Belgian mine. That is why Iguanodon remains a favourite among palaeontologists: not simply for what it was, but for what it taught us about how little we knew.