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ig - WAHN - oh - don

Copyright 2007

Field Notes

Name Means: "Iguana tooth"
Length: 33 feet (10 m)
Diet: Herbivore (Plant-Eater)
Time: Late Jurassic
Location: Western USA; Western Europe; Romania; Mongolia

In a way Iguanodon could be called a "founding father" of dinosaurs - not in the sense that it is ancestral to all other dinosaurs, but in terms of our scientific understanding of dinosaurs. In 1825, Iguanodon became the second dinosaur to be named by science, and it was one of the three animals around which the British paleontologist Sir Richard Owen constructed the scientific concept of "Dinosauria" in 1842. Ever since, studies and reconstructions of Iguanodon have played an important role in advancing our knowledge of dinosaurs in general.

Iguanodon was widespread in the Early Cretaceous - species have been described from Europe, North America, and Mongolia. The first fossils of this dinosaur to be found came from the Wealden rocks of southern England - rocks that were formed in an extensive series of shallow lakes and estuaries. The very first fossils were only teeth, which looked much like the teeth of living iguanas - hence the name. As more bones came to light, researchers reconstructed this dinosaur as a large quadrupedal herbivore - a sort of reptilian rhinoceros - and, in what turned out to be one of the most celebrated mistakes in the history of paleontology, a large bony spike that had been found with other parts of the skeleton was placed on the end of the nose. This early reconstruction helped to reinforce the perception of dinosaurs as lumbering animals - a perception we now know to be inaccurate.

It took one of the most remarkable fossil finds of all time to shake this stereotype. In 1878, workers in a coal mine in southern Belgium unearthed a large bone full of what they thought to be gold. The "gold" turned out to be "fool's gold" (pyrite), but the possibility of riches inspired further digging and led to the discovery of dinosaur skeletons. After three years, the complete skeletons of 31 Iguanodon had been recovered - at the time, they were the best preserved dinosaur fossils that had ever been found. Study of these specimens showed that, far from being a heavy, lumbering quadruped, Iguanodon was relatively light for its great length and could move on its back legs. These skeletons also put the nose spike where it belonged. In fact, Iguanodon had two spikes - one on each thumb.

For almost a century after that, Iguanodon, and other large ornithopods, such as the hadrosaurids, were reconstructed rather like colossal Kangaroos, standing on their hind legs with the head held high and the tail stretching out along the ground. It was not until the 1970s that new studies revealed that Iguanodon had strong front legs and that the central three fingers ended in hooves. This implied that Iguanodon spent some time on all fours, and prbably ran on its hind legs when it needed to move quickly. As in other ornithopods, its spine was supported by large, ossified tendons around the hips; unlike in other ornithopods, however, the tendon bundles were arranged diagonally in a trellis pattern, rather than parallel to each other.

The jaws and teeth of Iguanodon made it an afficient plant-eater. A formidable battery of closely packed cheek teeth were well suited to grinding up tough plant matter - the upper surface of each tooth was broad and ridged. The jaw bones that held the teeth moved upward and outward in the skull as the animal chewed, thus allowing the grinding surfaces to move against each other and thereby contributing to the efficiency of the chewing action. The same arrangement has been observed in a number of other ornithopods, but in Iguanodon it appears to have been particularly well developed.

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