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Conservation status: Fossil

Missing image

BBC's Walking with Dinosaurs reconstruction of Iguanadon
Scientific classification

I. anglicus
I. atherfieldensis
I. bernissartensis (type)
I. dawsoni
I. fittoni
I. hoggi
I. lakotaensis

Iguanodon was the first dinosaur recognized, the second dinosaur formally named and described, and with Megalosaurus and Hylaeosaurus, one of the three originally used to define the new classification, Dinosauria.


The Iguanodon is an ornithopod dinosaur, roughly halfway between the early "hypsilophodontids" and their ultimate culmination in the duck-billed dinosaurs. They lived between 120 to 140 million years ago, in the Barremian to Valanginian ages of the early Cretaceous period, though one unknown species is from the late Jurassic.

The various Iguanodon species are bulky herbivores, ranging from 6 to 11 metres (20 to 36 feet) in length, and averaging about 5 tonnes (5.5 tons) in weight.

Discovery and classification

Gideon Mantell's wife, Mary Ann, discovered the first tooth of an Iguanodon in the Tilgate Forest in England, in 1822. The tooth resembled that of an iguana, but was twenty times larger, so he named it Iguanodon, or "iguana-toothed", from iguana and the Greek word odontos ("tooth"). Based on isometric scaling, he estimated it might be up to 60 feet (18 metres) long.

A better specimen was discovered in a quarry in Maidstone, which Mantell was able to identify as an Iguanodon based on the tooth. The Maidstone slab allowed the first skeletal reconstructions and artistic renderings of the Iguanodon. The most famous mistake was the placement of a "horn", also discovered by Mantell's wife, on the nose of the dinosaur. The discovery of much better specimens of I. bernissartensis in 1878 revealed that the horn was actually a modified thumb, perhaps used for defense.

Missing image
Borough of Maidstone coat of arms (note the Iguanodon on the left)

Still encased in rock, the Maidstone slab is currently displayed at the Natural History Museum, in London. The borough of Maidstone commemorated this find by adding an Iguanodon to their coat of arms in 1949.

Iguanodon anglicus was the original type species, but the holotype was based on a single tooth, and only partial remains of the species have been recovered since. In March of 2000, the ICZN changed the type species to I. bernissartensis, which is known from dozens of skeletons, some of which are very complete.

Remains of the best-known Iguanodon species have been found predominantly in Belgium, England, Germany, Spain and France. Remains of similar animals have been found in Tunisia and Mongolia, and distinct species have been found in Utah and South Dakota.

The largest find of Iguanodon remains occurred in 1878 in a coal mine at Bernissart in Belgium. With the encouragement of Alphonse Briart, supervisor of mines at nearby Morlanwelz, Louis Dollo oversaw excavation and reconstructed the skeletons. Some were publicly displayed from 1882; the completed restoration makes an impressive display in the Royal Belgian Institute of Natural Sciences in Brussels.

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