They lived between 120 to 140 million years ago, in the Barremian to Valanginian ages of the Early Cretaceous Period, although one dubious species is from the Late Jurassic.

Iguanodon's most distinctive feature was a large razor-sharp 'thumb spike', probably used for defence against predators

The various Iguanodon species were bulky herbivores, ranging from 6 to 11 metres (20 to 36 feet) in length, and averaging about 5 tonnes (5.5 tons) in weight. Iguanodon's thumb spikes were perpendicular to the three main digits.

In early restorations, the spike was placed on the animal's nose. Later fossils revealed the true nature of the thumb spikes, although their exact purpose is still debated. It could have been used for defence, or for foraging for food.

Although Iguanodon normally walked on four legs, they could run on two legs which made them quite nimble despite their huge size. Much unlike the lumbering Polacanthus, a spiky herbivore who regularly accompanied an Iguanodon herd. Perhaps for mutual protection.

Iguanodon were one of the most successful dinosaurs ever to have lived. They populated every continent, with the European species probably being the largest and thrived on a variety of vegetation. One of the reasons why they were so successful is that while most herbivorous dinosaurs crudely sliced food with their teeth, Iguanodon were the first herbivores to have developed back teeth which they used to grind up even the toughest vegetation before swallowing. This ability to chew, sped up the digestion of even the toughest plant material.