Iguanodon lived in the Cretaceous Period, about 125 million years ago, across modern-day Europe and Asia. The first Iguanodon fossils were found in 1822 by Gideon Mantell, who was either an English geologist or physician. This was the second species to be described scientifically as a dinosaur, and its name means “Iguana tooth”. Iguanodon is closely related to the duck-billed dinosaurs which would come later, and some scientists believe that they should in fact be classified together. However, Iguanodon is still considered a member of the Iguanodontidae family, an Iguanodontid.
After being found and classified, several attempts at reconstructing the skeleton were made and, while it was reconstructed, it was not correct. It was understood that this animal was a reptile but the extra digit, the thumb, was placed as a spike on the nose rather than in the hand. It is unknown what function this thumb actually served, but it may have been used for defense or helped to hold leaves and ferns. Iguanodon was also posed in a strictly quadrupedal pose which, while not totally incorrect, is not a good representation of their abilities. Iguanodon could move easily from a four-legged to a two-legged stance. Further, displays continued to place Iguanodon’s tail on the ground, like a kangaroo, until very recently, when a horizontal spinal structure was recognized. These misunderstandings related to fossil placement is a great example of how much we can learn about animals from their fossils and how our understanding of extinct animals evolves over time.
Fossil remains of Iguanodon show that they likely lived in herds or at the very least traveled in numbers. A large number of trace fossils, largely tracks, show that they were quite common and widespread during their time. Iguanodon was a herbivore and its teeth, sloping and ridged, allowed them to tear up the leaves and ferns which made up their diet. The bones of their skull were also not tightly fused, which allows for greater mobility of the jaw, which would be useful for grinding up tough plant fibers. Iguanodon’s hands are built to grasp its food, with three fused fingers with nearly hoof-like nails.
Iguanodon could reach up to 33 feet in height and weighed up to 3.5 tons. That’s roughly 7,000 pounds. That means that they would be comparable in size and weight to an elephant. Their large size indicates that they probably would not have been able to move very quickly and likely could achieve speeds of only 14 miles per hour. This is half of a human’s running speed, about as fast as a snake.
Iguanodon went extinct before the end of the Cretaceous Period, a little less than 94 million years ago. Its descendents were Hadrosaurs, the duck-billed dinosaurs. Iguanodon lived in a transitional period between the light, bird-like herbivores of previous periods and the large and bulky herbivores which lasted until the Cretaceous extinction.
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