10 Lesser-Known Facts About Iguanodon

Full color drawing of Iguanodons in a primeval forest.

CoreyFord/Getty Images

With the sole exception of Megalosaurus, Iguanodon has occupied a place in the record books for a longer period of time than any other dinosaur. Discover some fascinating Iguanodon facts.

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It Was Discovered in the Early 19th Century

Complete Iguanodon skeleton at a museum.

Ballista at English Wikipedia/Wikimedia Commons/CC BY 3.0

In 1822 (possibly a couple of years earlier, as contemporary accounts differ), the British naturalist Gideon Mantell stumbled across some fossilized teeth near the town of Sussex on the southeast coast of England. After a few missteps (at first, he thought he was dealing with a prehistoric crocodile), Mantell identified these fossils as belonging to a giant, extinct, plant-eating reptile. He later named the animal Iguanodon, Greek for "iguana tooth."

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It Was Misunderstood for Decades After Its Discovery

A pencil drawing of Iguanodon made in 1859.
This early depiction of Iguanodon was created by Samuel Griswold Goodrich in 1859.

Samuel Griswold Goodrich/Wikimedia Commons/Public Domain

Nineteenth-century European naturalists were slow to come to grips with Iguanodon. This three-ton dinosaur was initially misidentified as a fish, a rhinoceros, and a carnivorous reptile. Its prominent thumb spike was mistakenly reconstructed on the end of its nose, one of the seminal blunders in the annals of paleontology. Iguanodon's correct posture and "body type" (technically, that of an ornithopod dinosaur) weren't fully sorted out until 50 years after its discovery.

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Only a Handful of Species Remain Valid

Close up of Iguanodon skull.

Ghedoghedo/Wikimedia Commons/CC BY 3.0

Because it was discovered so early, Iguanodon quickly became what paleontologists call a "wastebasket taxon." That meant that any dinosaur which remotely resembled Iguanodon was assigned as a separate species. At one point, naturalists had named no less than two dozen Iguanodon species, most of which have since been downgraded. Only I. bernissartensis and I. ottingeri remain valid. Two "promoted" Iguanodon species, Mantellisaurus and Gideonmantellia, honor Gideon Mantell.

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It Was One of the First Dinosaurs to Be Publicly Displayed

Iguanodon statues exhibit at the Crystal Palace.

Chris Sampson/Wikimedia Commons/CC BY 2.0


Along with Megalosaurus and the obscure Hylaeosaurus, Iguanodon was one of three dinosaurs to be displayed to the British public at the relocated Crystal Palace exhibition hall in 1854. Other extinct behemoths on display included the marine reptiles Ichthyosaurus and Mosasaurus. These weren't reconstructions based on accurate skeletal casts, as in modern museums, but full-scale, vividly painted, and somewhat cartoonish models. 

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It Belongs to the Ornithopod Family

Iguanodon statue on a rock pile outside.

Espirat/Wikimedia Commons/CC BY 4.0

They weren't nearly as big as the biggest sauropods and tyrannosaurs, but ornithopods (the relatively petite, plant-eating dinosaurs of the Jurassic and Cretaceous periods) have had a disproportionate impact on paleontology. In fact, more ornithopods have been named after famous paleontologists than any other type of dinosaur. Examples include the Iguanodon-like Dollodon, after Louis Dollo, Othnielia, after Othniel C. Marsh, and the two ornithopods mentioned above that honor Gideon Mantell.

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It Was an Ancestor of Duck-Billed Dinosaurs

Colorful illustration of a hardosaurid in its natural habitat.


It's difficult for people to get a good visual impression of ornithopods, which were a relatively diverse and hard-to-describe dinosaur family that vaguely resembled meat-eating theropods. But it's easier to recognize the immediate descendants of the ornithopods: hadrosaurs, or "duck-billed" dinosaurs. These much bigger herbivores, like Lambeosaurus and Parasaurolophus, were often distinguished by their ornate crests and prominent beaks.

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No One Knows Why Iguanodon Evolved Its Thumb Spikes

Iguanodon thumb spike, a Toryosaurus claw, and a human hand.

Drow male/Wikimedia Commons/CC BY 4.0, 3.0, 2.5, 2.0, 1.0

Along with its three-ton bulk and ungainly posture, the most notable feature of the middle Cretaceous Iguanodon was its oversized thumb spikes. Some paleontologists speculate that these spikes were used to deter predators. Others say they were a tool for breaking down thick vegetation, while still others argue that they were a sexually selected characteristic. That means that potentially, males with bigger thumb spikes were more attractive to females during mating season.

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What Do Iguanodons and Iguanas Have in Common?

Colorful iguana sitting on rocks.


Like many dinosaurs, Iguanodon was named on the basis of extremely limited fossil remains. Because the teeth he unearthed vaguely resembled those of modern-day iguanas, Gideon Mantell bestowed the name Iguanodon ("iguana tooth") upon his discovery. Naturally, this inspired some overly enthusiastic but less-than-educated 19th-century illustrators to immortalize Iguanodon, inaccurately, as looking like a giant iguana. A more recently discovered ornithopod species has been named Iguanacolossus.

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Iguanodons Probably Lived in Herds

Exhibit of an Iguanodon herd walking on the grass.

PePeEfe/Wikimedia Commons/CC BY 4.0

As a general rule, herbivorous animals (whether dinosaurs or mammals) like to congregate in herds to help deter predators, while meat-eaters tend to be more solitary creatures. For this reason, it's likely that Iguanodon foraged the plains of North America and western Europe in at least small groups, though it's troubling that mass Iguanodon fossil deposits have so far yielded few specimens of hatchlings or juveniles. This may be taken as evidence against herding behavior.

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It Occasionally Ran on Its Two Hind Legs

Full color drawing of Iguanodon standing on its hind legs.

DinosIgea/Wikimedia Commons/CC BY 4.0

Like most ornithopods, Iguanodon was an occasional biped. This dinosaur spent most of its time grazing peacefully on all fours, but it was capable of running on its two hind legs (at least for short distances) when it was being pursued by large theropods. North American populations of Iguanodon may have been preyed upon by the contemporary Utahraptor.

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Strauss, Bob. "10 Lesser-Known Facts About Iguanodon." ThoughtCo, Feb. 16, 2021, thoughtco.com/things-to-know-iguanodon-1093789. Strauss, Bob. (2021, February 16). 10 Lesser-Known Facts About Iguanodon. Retrieved from https://www.thoughtco.com/things-to-know-iguanodon-1093789 Strauss, Bob. "10 Lesser-Known Facts About Iguanodon." ThoughtCo. https://www.thoughtco.com/things-to-know-iguanodon-1093789 (accessed June 5, 2023).