Iguanodon bernissartensis ig-WAN-oh-don

"Iguana tooth"

Iguanodon silhouette — silhouette · Matthew Dempsey (CC-BY) via PhyloPic

Length: 10 m (33 ft) — About 10 m long, ~3 tonnes — large bipedal herbivore with thumb spikes.
Period: Early Cretaceous (126–122 Mya)
Place: Europe · Belgium · England · Germany
Food: Herbivore — Cycads, ferns, conifer needles — chewed by a sophisticated jaw that worked like grinding teeth.
Clade: Iguanodontia Dinosauria Ornithischia Cerapoda Ornithopoda Thumb-spiked plant-eaters, ancestors to hadrosaurs.

One of the first dinosaurs ever named, famed for its conical thumb spikes.

Iguanodon reconstruction by Davide Bonadonna — Reconstruction · Davide Bonadonna (CC-BY)

Iguanodon was the second dinosaur ever named, in 1825. The first scientists thought it was a giant iguana — they put its thumb spike on its nose, mistaking it for a horn. Decades later, when 38 complete skeletons were dug out of a coal mine in Belgium, paleontologists finally understood: the spikes were thumbs, the body was that of a giant bipedal plant-eater.

More about Iguanodon

Discovery

Named by Gideon Mantell · 1825 · England (fossil teeth from the Tilgate Forest area at Whitemans Green, Sussex)

Mantell acquired large fossil bones from a quarry at Whitemans Green around 1820. After herbivorous teeth turned up, he came to suspect a large plant-eating reptile, and he named the genus in 1825 as the species I. anglicus.

The name means "iguana-tooth," because its herbivorous teeth resembled those of an iguana.

Portrait of Gideon Mantell — Gideon Mantell An English geologist who named Iguanodon in 1825, making it the second type of dinosaur formally named from fossil specimens after Megalosaurus.

Did Mary Ann Mantell really find the first Iguanodon teeth?

A popular legend says Gideon Mantell's wife, Mary Ann, found the first teeth in 1822 while he visited a patient. There is no evidence he brought his wife on patient visits, and in 1851 Mantell admitted he had found the teeth himself, though he had earlier credited her in 1827 and 1833. The story's truth is uncertain.

For the curious → What were the thumb spikes actually for?

I. bernissartensis had conical thumb spikes that stuck out away from the three main digits. They may have been used for defense against predators or for foraging for food, but their exact function is still debated.

What we know

Second dinosaur ever named (after Megalosaurus), in 1825.
Iconic thumb spike — possibly defensive, possibly for cracking seeds.
38 complete skeletons found in a Belgian coal mine in 1878 — the famous Bernissart specimens.
Sophisticated chewing teeth that worked like a grinding mill.

What we guess

Whether the thumb spike was a weapon, a tool for breaking seeds, or both.
Whether it walked on two legs or four — modern view says it could do both depending on need.
How big the herds were — Bernissart suggests groups, but might be an accumulation.