Hypsilophodon foxii

Hypsilophodon foxii was a small bipedal neornithischian from the Early Cretaceous Wessex Formation of the Isle of Wight. Numerous skeletons, including juveniles, make it one of the best-known small ornithischians. It had a lightly built body, long hind limbs, a stiff balancing tail, a horny beak and closely packed cheek teeth for slicing vegetation. Victorian anatomists once reconstructed it as an armoured tree climber, but later study showed that its first toe was not opposable and that supposed armour belonged to another reptile. Modern reconstructions therefore place Hypsilophodon on the ground as a fast-moving browser.

Its fossils occur between approximately 130 and 125 million years ago. Values shown here are approximate and reflect the current curated seed dataset.

A short beak cropped plants, while teeth at the front of the upper jaw and ridged cheek teeth helped process food. The hands retained five fingers and could probably grasp, but the forelimbs were too short for normal four-legged walking. Long lower legs and feet supported efficient bipedal movement. Ossified tendons stiffened the back and tail. The first toe pointed forward rather than opposing the others, removing the anatomical basis for the old tree-climbing reconstruction.

• Small skull with a horny beak and front upper teeth
• Ridged cheek teeth suited to processing vegetation
• Five-fingered grasping hands
• Long hind limbs adapted for bipedal movement
• Forward-pointing first toe rather than an opposable climbing digit
• Long balancing tail stiffened by ossified tendons

The first remains were unearthed on the Isle of Wight in 1849 and were initially mixed into the complicated history of Iguanodon. Reverend William Darwin Fox later obtained the distinctive skull that became the name-bearing specimen. Thomas Henry Huxley recognized a separate animal and named Hypsilophodon foxii in 1869; his formal paper appeared in 1870. Continued collecting around Cowleaze Chine produced many additional skeletons and allowed Peter Galton's detailed 1974 monograph to correct the long-lived tree-climbing interpretation.

Discovery credit: Reverend William Darwin Fox.

Naming authors: Thomas Henry Huxley.

Hypsilophodon lived on the warm, seasonally wet floodplains represented by the Wessex Formation. Rivers, ponds and forested areas supported ferns, horsetails, cycads and conifers. The same ecosystem included large herbivores such as Iguanodon and predators including Neovenator. Fossils are concentrated along the southwest Isle of Wight coast; the map point is a generalized fossil region rather than an exposed specimen coordinate.

Its light build, long legs and stiff tail support agile ground-based locomotion. The beak and cheek teeth indicate herbivory, although occasional consumption of other foods cannot be tested directly. Several individuals found in the same area have been taken as possible evidence of grouping, but accumulation by water or repeated use of a locality can produce similar patterns. There is no direct evidence that Hypsilophodon climbed trees, carried armour, or had a specific top speed.

• Victorian displays once showed Hypsilophodon perched in trees, an idea its feet do not support.
• Plates once attributed to its skin actually came from an armoured crocodile relative.
• It retained five fingers on each hand.
• Every securely identified fossil comes from the Isle of Wight.
• An anatomically updated bronze reconstruction joined the Natural History Museum gardens in 2024.

A research repository is not necessarily a public exhibit. Loan and display status can change, so check with the institution before visiting.

1. 01
   Dinosaur collection

   Natural History Museum, London

   Open source
2. 02
   On Hypsilophodon Foxii, a new Dinosaurian from the Wealden of the Isle of Wight

   Thomas Henry Huxley · Quarterly Journal of the Geological Society of London 26, 3-12 · 1870

   Open source
3. 03
   The ornithischian dinosaur Hypsilophodon from the Wealden of the Isle of Wight

   Peter M. Galton · Bulletin of the British Museum (Natural History), Geology 25(1), 1-152 · 1974

   Open source
4. 04
   Hypsilophodon dinosaur directory entry

   Natural History Museum, London

   Open source