Iguanodon

Iguanodon was the second dinosaur to be scientifically named. Gideon Mantell published the name in 1825, inspired by a tooth that resembled those of modern iguanas. In 1842, Richard Owen used Iguanodon as one of three genera to define the Dinosauria, alongside Megalosaurus and Hylaeosaurus. Over the following 150 years, scientific understanding of its appearance shifted dramatically. It was first envisioned as a giant lizard, then as a bipedal animal that dragged its tail and had a horn on its nose. Today, it is correctly understood as a facultatively quadrupedal ornithopod with a large thumb spike.

This large herbivore reached roughly 10 m in length. It had a long, deep skull equipped with a broad beak and batteries of leaf-shaped teeth in the rear of the jaw. Its robust forelimbs supported four-legged movement, with the third and fourth fingers being hooved for weight-bearing. The first finger was the iconic thumb spike, while the fifth finger was long and prehensile. Its hindlimbs remained powerful and capable of supporting bipedal movement.

Between 1878 and 1881, miners in Bernissart, Belgium, discovered 38 articulated skeletons of Iguanodon bernissartensis over 300 m underground. This remains one of the most significant finds in the history of paleontology, providing the basis for early skeletal reconstructions and the type material for the species.

Iguanodon inhabited floodplain and lakeside environments alongside other ornithopods, ankylosaurs, and small predators. Evidence from the Bernissart assemblage and mixed-age trackways in England suggest these animals lived in social groups. Their complex chewing mechanism allowed them to process tough vegetation such as ferns, conifers, and early flowering plants. The conical thumb spike, which grew to about 15 cm long, likely served as a defensive weapon or was used in combat between individuals.

• Bernissart specimens (RBINS, including IRSNB 1534, 1561) — Royal Belgian Institute of Natural Sciences; 38 articulated skeletons.
• Holotype tooth (NHMUK GR 750) — the original Mantell specimen, Natural History Museum, London.
• Maidstone block (Mantell-Piece, NHMUK 3741) — early skeleton, Natural History Museum.

Genus splitting — Norman (2010) revised iguanodontian taxonomy substantially, separating various species formerly placed in Iguanodon into other genera (Mantellisaurus, Dollodon, Hypselospinus, Barilium). The current strict definition of Iguanodon contains essentially one well-supported species, I. bernissartensis. Posture history — Iguanodon was reconstructed as bipedal with tail-dragging through the early 20th century, then as facultatively quadrupedal from the 1980s onward. Thumb-spike function — defence vs combat vs both.

Iguanodon is the original dinosaur — alongside Megalosaurus, the first scientifically described, and the Crystal Palace concrete sculptures (1854) feature it prominently. Disney's Dinosaur (2000) cast it as the protagonist; it appears in many children's books and the Bernissart discovery is the subject of multiple museum exhibitions and dedicated paleontology documentaries.

• ornithopoda
• hadrosaurus
• parasaurolophus
• edmontosaurus

• Norman, D. B. (2010). A taxonomy of iguanodontians (Dinosauria: Ornithopoda) from the lower Wealden Group. Zootaxa, 2489, 47–66.
• Mantell, G. A. (1825). Notice on the Iguanodon. Philosophical Transactions of the Royal Society, 115, 179–186.
• Verdú, F. J., et al. (2017). New systematic and phylogenetic data about the early Barremian Iguanodon galvensis from Spain. Historical Biology, 29, 1031–1059.
• Bultynck, P. (1989). Bernissart and the Iguanodons. Royal Belgian Institute of Natural Sciences.