Living between 140 and 100 million years ago, large herd-dwelling herbivores called Iguanodons roamed the Earth. They were one of the first species to be called Dinosaurs.

Discovery

Dr Gideon. A. Mantell from Wikimedia Commons. Licenced by CC-By 2.0

The first person to identify Iguanodon was Dr Gideon Mantell. Although there is evidence that William Smith, in 1809, first discovered an Iguanodon bone near Cuckfield, Sussex.  Mary Mantell, accompanying her husband to Sussex, observed some large teeth in rubble by the side of the road. Subsequently, Gideon addressed experts on animals to determine the teeth’s origin. Some suggested that the teeth were comparable, but not the same, to that of a Pufferfish (Tetrahedron). Others suggested the teeth belong to reptiles. Yet, Gideon searched with little success, until he visited the Hunterian Museum in which, he saw something with similar dentition. This was in an Iguana skeleton, a newly discovered herbivore. Hence in 1825, Mantell named this prehistoric reptile Iguanodon, meaning Iguana tooth.

Progressive view of the Iguanodon

Richard Owen’s Iguanodon located at Crystal Palace, by Jes is licenced under CC-BY-SA 2.0

In 1834, a disarticulated skeleton was discovered at a quarry near Maidstone, Kent. Later nicknamed the ‘Mantell-piece’. It consisted of pelvic fragments, vertebrae, limb bones, teeth and rib fragments. Mantell attributed this to the Iguanodon, (although later reclassified as a species of Mantellisaurus), using it to draw the first Iguanodon skeleton. It looked very similar to the Rhinoceros Iguana (Cyclura cornuta).  However, by 1942, Richard Owen (the creator of the term Dinosaur) re-illustrated the Iguanodon to have a ‘rhino-like’ build, which he depicted through sculptures. Starting In 1878, miners in Bernissart Belgium Coal Mine, excavated 40 dinosaur skeletons in 5 years.  Subsequently, Louis Dollo revised the Iguanodon to be a 5 to 11 m tall kangaroo-like animal. Correlating with Mantell’s later studies, prior to the 1850’s, of the ‘Mantell-piece’. Describing the Iguanodon as bipedal. This interpretation remained unchanged for 60 years. Nevertheless, evidence now shows that this is broadly incorrect.

The Current view of the Iguanodon

Through studies of Iguanodon footprints and its bird-like pelvis, it became evident that Iguanodon walked predominately on all fours. Yet it had bipedal capabilities, although this is more apparent in juveniles. Bipedal movements allowed the Iguanodon to escape predation and reach higher in trees for food. This is evident through observing their ‘hands’. Its flexible, little finger was kept of the ground, allowing them to grasp food. The thumb spike was used in defence. The remaining 3 digits acted as a load bearing base with a hoof like appearance. Dollo’s ‘kangaroo tail’ believed to keep the animal upright, was an impossibility. His reconstruction seemed to involve deliberately breaking bones to achieve its form. Instead, the tail was horizontal. It acted as a cantilever to balance the weight of the upper body, which is lowered to the ground to allow the front limbs to contact the ground.

Iguanodon model by Peter Montgomery is licenced under CC BY-NC 2.0

The First Dinosaur to Chew

As Mantell suggested, Iguanodons were herbivores. Yet it remained a mystery on how they chewed. In order to accomplish this the animal needed cheeks, living reptiles don’t have these. However, the Iguanodons skull show that its teeth are on the inside of the jaw. Thus, it left room for a skin covering, acting as a cheek. The second mystery was grinding. Mammals move their jaws horizontally to accomplish this. Iguanodon can only move its jaw vertically. They overcome this by having a hinge that allows the upper jaw to flex. Pushing its lower jaw up inside the upper jaw allows the teeth to grind together. If it was possible to observe an Iguanodon chewing, the side of its head would gently expand and contract.