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, with the well-studied species Iguanodon bernissartensis living in Belgium, Germany, England, and Spain between about 126 and 122 million years ago. This dinosaur was large and bulky, measuring up to 9–11 metres (30–36 ft) long and weighing as much as 4.5 metric tons. It had distinctive large thumb spikes, possibly used for defense, and long, flexible fifth fingers helpful for grabbing food.

The genus was named by English geologist Gideon Mantell and 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. Over time, scientists have studied many fossils of Iguanodon, including nearly complete skeletons, which have helped them learn about how it lived, moved, and possibly behaved in groups. 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. It is said that Gideon Mantell’s wife, Mary Ann, found the first teeth of an Iguanodon in Tilgate Forest in Whitemans Green, Sussex, England, in 1822. However, there is no proof that Mantell brought his wife with him while visiting patients. Mantell himself later admitted that he found the teeth, though he had earlier claimed his wife discovered them. Mantell began studying large fossil bones from the same area in 1820, initially thinking they belonged to a giant crocodile. By 1821, he noticed herbivorous teeth and started to believe a large herbivorous reptile existed there.

In 1824, after comparing the teeth to those of an iguana, Mantell named his new animal Iguanodon, meaning "iguana-tooth." He estimated it could be up to 18 metres (59 feet) long. Mantell shared his findings with the Royal Society of London in 1822, but they dismissed the teeth as fish teeth or rhinoceros incisors. It was not until 1824, after consulting with Georges Cuvier, that the teeth were recognized as belonging to a large herbivorous reptile.

Bernissart mine discoveries and Dollo's new reconstruction

One of the most significant discoveries of Iguanodon fossils happened in 1878 in a coal mine in Bernissart, Belgium. Miners accidentally found skeletons, and further excavation revealed at least 38 Iguanodon individuals. In 1882, the scientist Louis Dollo reconstructed these skeletons, showing that earlier ideas about the dinosaur’s shape were incorrect. Dollo’s reconstruction, inspired by cassowary and wallaby animals, placed a spike on the thumb instead of the nose and influenced how Iguanodon was viewed for many years.

Turn of the century and the Dinosaur Renaissance

Research on Iguanodon slowed during the early 20th century due to World Wars and the Great Depression. However, new findings and studies in the late 20th century helped scientists better understand how Iguanodon lived and fed. Discoveries in Germany showed that these dinosaurs often lived in groups. Scientists also corrected earlier mistakes in how they imagined Iguanodon’s body, realizing that its tail was straight, not bent.

21st century research and the splitting of the genus

In the 21st century, scientists have used Iguanodon fossils to search for ancient proteins and other biomolecules. Some researchers have also suggested splitting Iguanodon into several different genera based on differences between fossils found in various locations. These debates continue as scientists learn more about these fascinating dinosaurs.

Description

Iguanodon were large, bulky herbivores that could walk on two legs or four. The best-known species, I. bernissartensis, was about 9 metres (30 feet) long, but some may have reached 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, possibly used for defense or finding food. Their legs were strong but not built for fast running. They had tall, narrow skulls with beaks and teeth similar to iguanas, though much larger. Their teeth were packed closely together, and they likely had cheeks to help hold food in their mouths while eating.

Classification and evolution

Iguanodon is part of a large group of dinosaurs called Iguanodontia, which 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 used to place many of these dinosaurs in a family called Iguanodontidae, but now they understand that this group was too broad. Today, only Iguanodon is classified under Iguanodontidae. Iguanodon is closely related to Camptosaurus and Ouranosaurus, and scientists study their family tree to learn more about their evolution.

Species

Because Iguanodon was one of the first dinosaurs ever named, many species have been linked to it over time. Today, scientists agree that only two species truly belong to Iguanodon.

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

Many other names once linked to Iguanodon have been moved to different genera or are considered too uncertain to classify clearly. For example, I. atherfieldensis is now called Mantellisaurus, and I. dawsoni is now known as Barilium. Some names, like I. anglicus, were used early on but are no longer considered valid types for this genus.

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, helping 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, leading scientists 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.