Hypsilophodon, meaning “high-crested tooth”, is a genus of ornithopod dinosaur from the Early Cretaceous Period of what is now Europe. It was discovered in 1849. It was first described as an Iguanodon and not until 1870, when T.H. Huxley studied it, was it described as a Hypsilophodon. Three nearly complete skeletons along with several minor finds have been found on the Isle of Wight and other southern European countries, including England and Portugal.

Hypsilophodon was a small bipedal dinosaur. It reached about 6.6 feet in length and weighed about 110 to 150 pounds. Its body was built for running and speed. It had long legs, a stiff tail, and its posture was very aerodynamic. Its stiff tail was used for balance and would allow the creature to run very fast. Due to its small size, it most likely subsisted on a diet of low-growing plant matter, such as shoots and roots. The structure of the skull reveals that it had teeth which were set far back into the jaw. In turn, this suggests that it had cheeks, an advanced feature that allows for holding food in the mouth while chewing. The teeth appeared to have been self-sharpening. Its teeth would have been continuously replaced throughout life.

Although not much is known about its parental care, the finding of a neatly-arranged nest suggests that some care was taken before eggs hatched. It is possible that these dinosaurs moved in herds, as large groups have been found in fossil beds. Hypsilophodons have been labeled “deer of the Mesozoic”, due to their herd-like nature. It was previously suggested (since 1882) that this dinosaur may have been able to climb trees in order to find shelter. However, Peter M. Galton provided accurate musculoskeletal analysis of the animal in 1974 that convinced most paleontologists that Hypsilophodon was a strictly terrestrial dinosaur. Another misconception was the belief that this was an armored dinosaur.

Despite living in the last era of the dinosaurs, this was a fairly primitive genus. It had five digits on the hands, and only four on the feet. Most dinosaurs lost these redundant features by the onset of the Cretaceous era. It also had pointed triangular teeth in the front of the jaw, a feature most herbivores lost by this era. Hypsilophodon remained fairly common from the Late Jurassic to the end of the Cretaceous period. It is possible that this is due to near perfect adaptation of its lifestyle, and it is assumed selective pressure was low for this genus of dinosaur.

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