Iguanodon was a large ornithopod that lived during the Early Cretaceous Period. The ornithopods (the name means "bird feet", after their three-toed feet) were a group of ornithischians that developed the ability to chew their food. Iguanodon was capable of standing and walking on either two legs or four. Its long hindlegs had three toes and hoof-like nails, while the three middle fingers on its hands could be splayed wide to form a foot when on all fours. The other two digits on its five-fingered hands were a spiked thumb and flexible fifth finger for grasping. Iguanodon would have gathered its food using this flexible finger. It had a prominent snout and powerful, beak-like jaws for cropping off twigs and shoots.

Teeth

Iguanodon means “iguana tooth”: its tall cheek teeth resembled those of a modern iguana, a large lizard. Iguanodon’s teeth were positioned in its jaws in such a way that the upper teeth rubbed against the lower ones, grinding anything caught in between. Old worn teeth were replaced with new ones throughout its life.

Stance

Having long bones in its back legs gave Iguanodon the ability to move about bipedally (on two legs). The hooves on the ends of its fingers show that it must have walked on all fours as well—probably its usual way. Infants, which had proportionally shorter arms, spent more time running on two legs. Studies of fossil tracks confirm this. Iguanodon would have held both its back and stiffened, flat tail horizontal. Being able to take to two legs would have helped it run away from predators at speed.

It is likely that Iguanodon roamed around in herds, as part of a safety-in-numbers defence strategy. A group of fossil remains found close together suggest a herd was drowned in a flash flood.

Fossil remains

Iguandon’s fossil remains were first discovered in 1822. It was only the second dinosaur to be discovered, after Megalosaurus. The word “dinosaur” had yet to be invented. In an early reconstruction of Iguanodon, it was depicted as a sturdy, four-legged, bear-like animal with its spike on its nose. Later it was given an upright, kangaroo-like stance, before the modern version, with a near-horizontal backbone, was adopted.

Facts about Iguanodon

Pronunciation: Ig-WAH-noh-don

Size: 10 m (33 ft) long and 3 m (10 ft) tall

Where and when: Swamps and meadows in Europe 126–122 million years ago (Early Cretaceous)

Diet: Ferns, horsetails, cycads

Predators: Eotyrannus, Neovenator

Features: Large, spiked thumb for defence; cheek teeth for chewing vegetation; self-sharpening teeth; ability to run on two legs allowed it to escape from predators at speed; ability to rear up on muscular back legs to reach tree leaves

Relatives: Muttaburrasaurus (Australia); Ouranosaurus (Africa); Dryosaurus, Camptosaurus (Europe and North America)