Iguanodon

Iguanodon

Iguanodon (/ɪˈɡwɑːnədɒn/ i-GWAH-nə-don; meaning 'iguana-tooth'), named in 1825, is a genus of iguanodontian dinosaur. It lived during the Late Jurassic to Early Cretaceous periods. The well-studied species Iguanodon bernissartensis lived in Belgium, Germany, England, and Spain between about 126 and 122 million years ago.

This dinosaur was large and bulky. It measured up to 9–11 metres (30–36 ft) long and weighed as much as 4.5 metric tons. It had large thumb spikes, possibly used for defense, and long fingers helpful for grabbing food.

The genus was named by English geologist Gideon Mantell. It was the second dinosaur to be formally named, after Megalosaurus. It helped define what scientists call Dinosauria. Iguanodon belongs to a group known as Iguanodontia, which also includes the duck-billed hadrosaurs. Scientists have studied many fossils of Iguanodon, including nearly complete skeletons. This has helped them learn about how it lived and moved. Because of this, Iguanodon has become a well-known and important dinosaur in both science and popular culture.

Discovery and history

Gideon Mantell, Sir Richard Owen, and the discovery of dinosaurs

The story of how the dinosaur Iguanodon was discovered is often surrounded by legend. Gideon Mantell found the first teeth of an Iguanodon in Tilgate Forest in Whitemans Green, Sussex, England, in 1822. At first, he thought the bones might belong to a giant crocodile. But later, he noticed teeth that looked like those of a plant-eating animal.

In 1824, after comparing the teeth to those of an iguana, Mantell named his new animal Iguanodon, meaning "iguana-tooth." He thought it could be up to 18 metres (59 feet) long. At first, others did not believe him, but later they began to understand that these were the bones of a large plant-eating reptile.

Bernissart mine discoveries and Dollo's new reconstruction

In 1878, miners found many Iguanodon skeletons in a coal mine in Bernissart, Belgium. Scientists later studied these skeletons and changed their ideas about what Iguanodon looked like. The scientist Louis Dollo created a new model of the dinosaur, showing it had a spike on its thumb instead of its nose. This changed how people thought about Iguanodon for many years.

Turn of the century and the Dinosaur Renaissance

Research on Iguanodon slowed during the early 20th century. However, new discoveries in the late 20th century helped scientists learn more about how Iguanodon lived. They found that these dinosaurs often lived together in groups. Scientists also learned that its tail was straight, not bent.

21st century research and the splitting of the genus

In the 21st century, scientists have studied Iguanodon fossils to learn about ancient proteins and other materials. Some scientists have suggested dividing Iguanodon into several different groups based on differences in fossils found in various places. These discussions continue as scientists discover more about these interesting dinosaurs.

Description

Iguanodon were large, heavy dinosaurs that ate plants. They could walk on two legs or four. The most famous kind, I. bernissartensis, was about 9 metres (30 feet) long, but some might have been up to 11 metres (36 feet). They weighed around 4.5 metric tons.

These dinosaurs had long arms with strong hands. Their thumbs had sharp spikes, maybe for protection or to help find food. Their legs were strong but not made for quick running. They had tall, narrow heads with beaks and teeth like iguanas, but much bigger. Their teeth were packed closely together, and they probably had cheeks to keep food in their mouths while they ate.

Classification and evolution

Iguanodon is part of a large group of dinosaurs called Iguanodontia. This group includes many species from the Middle Jurassic to the Late Cretaceous. Well-known members of this group are Dryosaurus, Camptosaurus, Ouranosaurus, and the duck-billed hadrosaurs. Scientists once thought many of these dinosaurs belonged to a family called Iguanodontidae, but now they know this group was too big. Today, only Iguanodon is classified under Iguanodontidae. Iguanodon is closely related to Camptosaurus and Ouranosaurus. Scientists study their family tree to learn more about how they evolved.

Species

Iguanodon was one of the first dinosaurs ever named. Over time, many species were linked to it. Today, scientists say only two species truly belong to Iguanodon.

The main species is I. bernissartensis. It was described in 1881 and is famous for the many complete skeletons found in Belgium. Another accepted species is I. seelyi. It was found on the Isle of Wight and named after a local landowner.

Many other names once linked to Iguanodon have been moved to different groups or are not clearly classified. For example, I. atherfieldensis is now called Mantellisaurus, and I. dawsoni is now known as Barilium. Some early names, like I. anglicus, are no longer considered valid types for this group.

Palaeobiology

Feeding

One of the first things noticed about Iguanodon was that it had teeth like a plant-eating reptile. Early scientists thought it might have had a tongue like a giraffe to grab food, but later discoveries showed this was wrong. Instead, its skull was built so that when it closed its mouth, the teeth in the upper jaw would grind against the teeth in the lower jaw. This helped it chew tough plants. The front of its mouth had a beak-like edge to bite off twigs and shoots.

Exactly what Iguanodon ate is still debated. Because of its size, it could have reached food from the ground up to trees about 4–5 metres tall. Some scientists think it ate horsetails, cycads, and conifers, while others believe it may have eaten early flowering plants. Whatever it ate, Iguanodon was a big plant-eater and an important part of its ecosystem.

Posture and movement

Early fossils of Iguanodon were incomplete, so scientists had to guess about how it moved. At first, it was thought to walk on all fours with a dragon-like face. But when more complete skeletons were found, it became clear that Iguanodon could walk on two legs. Later studies showed that its tail was stiff, so it probably spent a lot of time on all fours, especially as it grew bigger. Its hands had three fingers that could support its weight, and it could walk on its fingers and toes.

Thumb spike

Iguanodon had a large, spike-like thumb claw on each hand. This spike was once thought to be on its nose, but we now know it was on its hand. It might have been used to defend itself against predators, or perhaps to break open seeds and fruits.

Possible social behaviour

Fossils of many Iguanodon found together do not necessarily mean they lived in herds. Some scientists think these fossils came from animals that died in floods and ended up in the same place. Other findings suggest that some Iguanodon may have moved in groups, but there is no clear proof.

Paleopathology

Some Iguanodon fossils show signs of injuries, like a broken hip bone, and others show signs of arthritis, which is wear and tear in the joints.

In popular culture

Since it was first described in 1825, Iguanodon has been a popular dinosaur in books, movies, and games around the world. In 1852, two full-size models of Iguanodon were built at the Crystal Palace in London. These early models looked like elephants and had horns, but they were the first ever full-sized dinosaur models made.

Iguanodon has appeared in many films and TV shows. In the Disney movie Dinosaur from 2000, an Iguanodon named Aladar is the main character. The dinosaur also inspired the famous monster Godzilla, along with Tyrannosaurus rex and Stegosaurus. It has been in The Land Before Time films and episodes of TV shows too. Documentaries like Walking with Dinosaurs and Dinosaur Britain have also featured Iguanodon.