Iguanodon: the thumb-spiked herbivore that started the science

When and where

Iguanodon lived during the Early Cretaceous, roughly 135 to 125 million years ago, across what is now Europe, with the richest fossil deposits in Belgium and southern England. The Wealden Group of southern England produced the original teeth that started the science of dinosaur paleontology, and the Bernissart coal seam in Belgium produced the largest single concentration of dinosaur skeletons ever found. The European environment of the period was a network of low-lying river deltas and forested floodplains, comfortable browsing country for a herbivore the size of a small lorry.

How we know

Iguanodon owns a foundational place in the history of paleontology. Gideon Mantell described the genus in 1825, two years after his wife Mary Ann Mantell found teeth in a Sussex roadside, making it the second dinosaur ever formally named after Megalosaurus. In 1878, miners at the Bernissart pit in Belgium broke through into a fossil-filled fissure containing at least 38 articulated Iguanodon skeletons, the result of a herd that had fallen into a flooded ravine in the Early Cretaceous and been preserved together. Those specimens are still on display at the Royal Belgian Institute of Natural Sciences in Brussels. The Bernissart finds also corrected an early reconstruction error: the conical bone Mantell had placed on the snout as a "horn" was relocated to the thumb, where it actually belonged. Source: Wikipedia entry on Iguanodon.

What set it apart

Iguanodon's hand was the giveaway. Five fingers, each with a different job: a conical thumb spike for defence and possibly food handling, three weight-bearing middle fingers held in a hoof-like cluster for quadrupedal walking, and an opposable fifth finger flexible enough to grip vegetation. That hand design lets paleontologists reconstruct the animal's posture with confidence, alternating between two-legged browsing and four-legged walking depending on speed. Adults reached 10 metres in length and 3 to 4 tonnes in weight. The teeth, ridged and packed in shearing rows, gave the genus its name, since they reminded Mantell of an iguana's. Iguanodon was the workhorse herbivore of Early Cretaceous Europe, the way Triceratops was for the Late Cretaceous of North America.

For collectors and classrooms

A scaled Iguanodon figurine carries genuine teaching value because the hand is so unusual. Look for a model that shows the thumb spike clearly and the three weight-bearing middle fingers held in a cluster. Browse a hand-painted figurine.