Since the discovery of a few of its fragmented fossil bones and teeth in 1822 the Iguanodon has undergone many controversies on how not only the animal in question looked, but its habits, social life, and posture. From the first mistaken placement of its thumb horn on the end of its nose to the theory that it stood on four pillar-like legs with a stubby neck to the theory that its tail dragged behind it while grazing bi-pedal, nothing points to commonality. After some questions were answered with the findings of complete skeletons, the question remains; was the animal a quadruped, biped, or both?
The first thing to look at is not the skeletal structure (since that’s being debated) but the other fossil evidence: footprints. A dinosaur’s footprints would greatly help to solve the mystery of the beast in question. Unfortunately, while footprints have been found many are in question whether they actually belonged to the Iguanodon or not. Within the limited findings there have been discrepancies between prints. Some show that the dinosaur walked on all fours with two larger three-toed footprints and a smaller set of a five-toed print, while others show only the rear footprints which could easily belonged to other species. The debate is still in the air for concrete evidence.
As the footprint record didn’t sway the argument to either side, the skeleton is all that is left. Due to the discovery of complete skeletons the specific configuration of the animal was no longer in question, but how it walked was. By analyzing the skeletal structure it is easy to eliminate several of the previous conjectures. The first is that it didn’t have the horn on its head since it was a thumb spike, the second was the front and rear legs are different in size eliminating the pillar-legged theory, and third, its tail bones near the pelvis region are too ridged to have let it bend in a vertical direction thus ruling out the dragging theory. Instead the structure shows that the animal would have large load-bearing hind legs that would have done well to support the bulk of its hind body and the weight of its tail. Though slightly smaller, the front legs would also be able to bear weight from the chest region and would likely not have had such lengthy and supportive bones if they were not meant for walking. This structure certainly goes towards supporting the quadrupedal tendency of the animal.
However, load-bearing members do not confirm a solely four-legged theory. With the much wider spaced toe support on the hind legs, weight could just have easily been shifted back to allow limited bipedal movement useful for higher grazing and defense. Using the front toe spikes for fighting a bipedal stance would be required, an easy enough weight shift accommodated by using its tail as a counter balance, which would normally be used to offset the animal’s weight and force the majority of it on the hind quarters. But to use the bipedal stance for long durations is out of the question, which means the animal had to use both interchangeably depending on its situation. Therefore the construction of the skeletons to depict either orientation is correct.
