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ten - ON - toh - SAW - rus
Name Means: "Tendon lizard"
Most ornithopod dinosaurs have strong tendons running along their backbone in the hip region. On Tenontosaurus these tendons were so well developed that they inspired the dinosaur's name. These thick tendons were ossified (strengthened with bone) and were arranged in bundles that ran parallel to the length of the spine. As a result, the spine of this dinosaur, from the lower back to the upper tail, would have been very stiff. This would have helped the animal to support the weight of its body across its hips; the torso was held stiffly in front of the hips and was balanced by the tail, which stretched out horizontally behind. Because the spinal column was almost parallel to the ground, the tail, which was very thick and bulky, would have been held high. This is confirmed by trackways of ornithopods which show no signs of marks made by tails dragging along the ground.
Tenontosaurus fed on plant matter, which it broke off with its horny beak and then chewed with its teeth, all of which were at the back of its mouth. The small, swift-moving Deinonychus was Tenontosaurus's main enemy. The teeth of this predator have been found along with Tenontosaurus skeletons. Some scientists therefore believe that Deinonychus hunted the larger animal in packs, but there is no real evidence to support this. In spite of what would seem to be the advantages of having clawed feet and a huge tail, Tenontosaurus would have been easy catch for packs of sharp-fanged deinonychus.
There is still debate about the proper classification of this dinosaur-some maintain it was an advanced hypsilophodontid while others argue that it was an early iguanadontid. Tenontosaurus does appear to have been a transitory form between the smaller ornithopods, such as Dryosaurus, which arose in the Jurassic, and the larger ornithopods, such as Iguanadon, which arose in the Cretaceous.