WHEN HYPSILOPHODON LIVED
Hypsilophodon lived in the early Cretaceous Period, about 125-120 million years ago.

BEHAVIOR
A bonebed of about 20 Hypsilophodon fossils were unearthed together on the Isle of Wight (an island off the coast of southern England). This indicates that a herd of Hypsilophodon died together.

They laid eggs and may have cared for their young for at least a little while. This is evidenced by eggs found carefully placed in Hypsilophodontid nests.

INTELLIGENCE
Hypsilophodon was an ornithopod, whose intelligence (as measured by its relative brain to body weight, or EQ) was midway among the dinosaurs.

DISCOVERY OF FOSSILS
Hypsilophodon was first described by Thomas Huxley in 1870; paleontologists of that time thought that Hypsilophodon was quite similar to the modern-day tree kangaroo. For over 100 years, scientist believed that Hypsilophodon lived in trees. In 1974, paleontologist Peter M. Galton's reconstruction of Hypsilophodon showed that there is no evidence for tree-dwelling behavior, and that Hypsilophodon was a terrestrial dinosaur.

Fossils of Hypsilophodon, and many other Cretaceous species (Iguanodon, crocodilians, turtles, fish, insects, mammals, and plants) have been found on the Wealden of southeast England and on the Isle of Wight. About 20 Hypsilophodon fossils were found together on the Isle of Wight (off the southern coast of England). Other Hypsilophodon fossils have been found in Spain.

CLASSIFICATION
Hypsilophodon was an herbivorous Ornithischian dinosaur, belonging to the Suborder Ornithopoda, Family Hypsilophodontidae (gazelle-like, herbivorous, herding dinosaurs which included Dryosaurus, Othnielia, Tenotosaurus, Parksosaurus, and Thescelosaurus). Hypsilophodontids probably gave rise to the duck-billed dinosaurs, like the pachycephalosaurs. The type species is H. foxii, Huxley, 1869.