Hypsilophodon ("high-ridged tooth") is an ornithopod dinosaur type from the Cretaceous period.

Discoveries and species

The first leftovers of Hypsilophodon ("high-ridged tooth") were improved in the early days of paleontology, in 1849. However, at the time the bones were consideration to belong to a young Iguanodon. It wasn't until 1870 that paleontologist T. H. Huxley was able to issue a full description of Hypsilophodon as we know it today. He had been provided with a number of skeletons by the priest William Darwin Fox, after whom the first species of Hypsilophodon was named.

Since then, three near-complete and over twenty minor finds have been made, particularly on the Isle of Wight, south of England. Other finds have been made in southern England, Portugal and South Dakota.

There is only one known species of Hypsilophodon, Huxley's original H. foxii. Galton and Jensen named one more species, H. wielandi in 1979, but it now seems likely this was just a variant individual within H. foxii.

Description

Hypsilophodon was in the middle of the smallest of the dinosaurs. While not fairly so small as for example Compsognathus, Hypsilophodon was only around 2.3 meters in length, and would have reached about waist height on a modern man. It weighed around 70kg. It ran on two legs and was herbivorous. It appears that it was clever to hunt for itself on hatching - there was no parental care after the eggs had hatched, although a neatly-arranged nest has been establish, suggesting that some care was taken previous to hatching.

Despite existing in the last of the periods in which dinosaurs feint the earth, the Cretaceous, Hypsilophodon had a number of extraordinarily primitive features. For example, although it had a beak like most ornithischians, it still had sharp triangular teeth in the front of the jaw. Most herbivorous dinosaurs had, by this stage, become sufficiently specialized that the teeth had been in total lost. Also, there were five digits on each hand, and four on each foot - most dinosaurs had lost these redundant features by the Cretaceous period.

In fact, the group Hypsilophodontia remained extraordinarily static from the late Jurassic to the end of the Cretaceous. This was because their basic structure was perfectly adapted to their life style and selective pressure, it is unspecified, was low. The entire body was built for speed while running: the light-weight minimized skeleton, low, aerodynamic posture, long legs and stiff tail for equilibrium all allowed it to travel remarkably fast for its size. Most Hypsilophodontids, like Valdosaurus remained small, although one (Tenontosaurus) grew to 6.5 meters long! Due to its small size, Hypsilophodon would have eaten low-growing vegetation and evaded probable predators of the time - such as Baryonyx and Megalosaurus by sprinting away in the thick forests that covered much of the landscape at the time.