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Isle of Wight dinosaurs. Picture courtesy of the artist John Sibbick. www.johnsibbick.com

Hypsilophodon foxi

Hypsilophodon foxi


The genus name, Hypsilophodon, (pronounced hip-si-lof-o-don) means high-ridged tooth; and the species name, foxi, is after Reverend William Fox, a Victorian fossil collector who found several specimens of Hypsilophodon.  The original species name was foxii but the last i is commonly dropped in today’s usage.  The Hypsilophodons were terrestrial (living on land), cursorial (running) bipeds (walking on two feet).  They may very well be the most famous British dinosaur, after Iguanodon, and are mostly represented by juveniles.  They are found in a layer of rock called the Hypsilophodon Bed within the Wessex Formation that is of Early Cretaceous age (Late Barremian), being about 125 to 129 million years old.  The locality that they are known from on the Isle of Wight is at Cowleaze Chine, near Barnes High.

For those who require more scientific information about Hypsilophodon we can describe the morphology (shape and other body features) in a little more detail.

Hypsilophodons were relatively small dinosaurs, ranging from about 1 to 3 metres in length and were similar to other ornithopods in many ways. They did, however, have some pretty unique features that can be used to distinguish them from other dinosaurs.

They had tall, short-snouted skulls that were quite small compared to their bodies and featured very large orbits (the aperture that houses the eye). The quadratojugal bone (between the jugal and quadrate) is quite large, having a large hole in it. They had 5 premaxillary teeth (teeth that are at the front of the upper jaw) which were serrated and constricted at the base of the crown. Their remaining teeth were compressed at the inner (lingual) and outer (labial) sides with expanded crowns and were only covered with enamel on one side, having ridges in the centre and serrations at the edges of these surfaces. The 12 maxillary teeth (the teeth in the upper jaw) had enamel covering the labial surface while the 13 dentary teeth (teeth positioned on the lower jaw) were covered with enamel on the lingual surface and featured a mid-line vertical ridge that formed a spike in the middle of the crown. These surfaces were likely used to shred tough vegetation.

Their femurs (thigh bone) have a fourth trochanter (a bony projection) that is positioned closer to the hip than in other ornithopods.

They may have also possessed two rows of osteoderms along their backs, however, more recent studies by Richard Butler and Galton suggest that they were instead plates of cartilage that were positioned between the ribs to strengthen the ribcage while running.


The first specimen was found at Cowleaze Chine in 1849 and was initially thought to be a juvenile Iguanodon fossil.  The specimen was contained within a mass of stone and consisted of a skeleton that lacked a head.  This specimen was broken into two parts and sent to both James Bowerbank and Gideon Mantell to identify.  When Richard Owen viewed the skeleton in 1854, he concluded that it was that of a juvenile Iguanodon.

Fox found another specimen at the same locality in 1868. This fossil possessed a skull and was a bit different from that of Iguanodon.  Fox noticed these differences and thinking it belonged to a new species of Iguanodon, sent the specimen to Thomas Henry Huxley who had the honour of identifying and describing it in 1869.  Fox was not actually far from being correct, as Hypsilophodon and Iguanodon are both ornithopod dinosaurs (meaning “bird-foot”).  Huxley concluded that both this specimen and the one from 1849, which is now the paratype, belonged to the same species of dinosaur and were not from an Iguanodon.  Fox was not very happy with Huxley’s idea and took the fossil away from Huxley, giving it to Owen instead.  Owen also disagreed with Huxley and was quoted saying “The conclusions of the author as a generic relationship of the species to which this unique fossil skull belonged, were not, however, satisfactory to its discoverer, and here, consequently placed in my hands.”  in 1874. Huxley was correct but Owen decided that the new skeleton belonged to a new type of Iguanodon.  This fossil was then deemed the holotype, labelled as NHMUK (Natural History Museum, United Kingdom) R197 and consisting of a well-preserved skull with teeth.  Later work was done on a large amount of material by John Hulke in the 1870s, who considered Hypsilophodon to be arboreal (living in trees).

Peter Galton then looked at this material, making it the subject of his University of London doctorate at King's College in 1967. He then went on to extensively re-describe it in 1974, suggesting a cursorial (running) lifestyle.


Hypsilophodon foxi

Hypsilophodons are almost exclusively collected from the “Hypsilophodon Bed” in the cliffs and sea floor close to Cowleaze Chine, on the Isle of Wight. Only remains from the Isle of Wight have been confidently identified as Hypsilophodon. Relative members of the genus have also been reported from mainland Sussex, from Spain, Portugal, Romania and also from the United States by their teeth and other small fragments but their identification is still questionable and was described by Galton in 2009. They are preserved in various ways, ranging from nearly complete, almost three-dimensional skeletons to brecciated and re-cemented disarticulated bones.

A family of Hypsilophodon at Dinosaur Isle

Once a skeleton has been re-assembled the work can begin on 'fleshing out' what we think the living creatures may have looked like.  Here a speculative colour scheme has been reproduced by model-maker Andrew Cox of a family of Hypsilophodon.  The gregarious nature appears to be supported by finding numbers of fossilised bones of different size animals in close proximity to each other.

The Science

Systematic palaeontology
 Owen, 1842
Ornithischia  Seeley, 1887
Ornithopoda  Marsh, 1881
Hypsilophodontidae  Dollo, 1882
Hypsilophodon foxii Huxley, 1869
Synonymous with Iguanodon foxii Owen, 1873

Hypsilophodons are widely researched, with numerous references in papers produced over the last few decades.  Perhaps one of the most prolific researchers throughout the 1970's was Peter Galton, of the Department of Biology, University of Bridgeport, Connecticut, U.S.A.  He produced one of the most detailed descriptions of Hypsilophodon in 1974, along with a number of other publications on Hypsilophodon and other ornithopods.  His work is still relevant today.

Over time we hope to be able to update the references on this webpage with further research articles.

Batten, D. J. (2011). English Wealden fossils. Henry Ling Limited, Dorset Press, Dorchester, UK.

Butler, R.J. & Galton, P.M. (2008). The 'dermal armour' of the ornithopod dinosaur Hypsilophodon from the Wealden (Early Cretaceous: Barremian) of the Isle of Wight: a reappraisal. Cretaceous Research. 29. 636-642.

Galton, P.M. (1974). The ornithischian dinosaur Hypsilophodon from the Wealden of the Isle of Wight. Bulletin of the British Museum (Natural History) Geology. London. Vol 25 No. 1. 1-152.

Galton, P.M. (2009). Notes on Neocomian (Lower Cretaceous) ornithopod dinosaurs from England - Hypsilophodon, Valdosaurus, "Camptosaurus",  "Iguanodon" - and referred specimens from Romania and elsewhere. Revue de Paleobiologie. 28. 211-273

Lomax, D. R & Tamura, N. (2014). Dinosaurs of the British Isles. Siri Scientific Press, Manchester, UK.

Martill, D. M & Naish, D. (2001). Dinosaurs of the Isle of Wight. Henry Ling Limited, Dorset Press, Dorchester, UK.

Thulborn, R. A. (1982). Speeds and gaits of dinosaurs. Palaeogeography, Palaeoclimatology, Palaeoecology. 38. 227-256.

Some facts and figures

1 to 3 metres long.

to be announced.

Plants, but possibly omnivorous.

How fast could it run?
10 to 20 miles per hour.

The geology and age
Early Cretaceous (Barremian) 125-129 million years.
Wealden Group
Wessex Formation (Hypsilophodon Bed).

Where was it found?
Cowleaze Chine (near Barnes High), Isle of Wight.

When was it first found?

Something different or unusual?
Most plant eating dinosaurs lost their premaxillary teeth as they evolved but Hypsilophodons did not.  They also possessed four toes on each hind foot while other bipedal dinosaurs usually reduced that number down to three.

Environment and adaptation

Hypsilophodon was initially thought to be an arboreal animal, being able to climb trees and rocks in order to take shelter.  This was suggested by John Hulke in 1882 who thought that one of the four toes were opposable to the others.  A reconstruction of this was made in 1912 by Othenio Abel with the animal using this toe to grasp branches and perches similarly to modern day birds.

This all changed when Peter Galton re-examined the skeleton in 1974, concluding that there were many features disproving this lifestyle, such as an immobile forearm and toes and fingers that were unsuitable for grasping.  Instead, he suggested a bipedal animal with a terrestrial, cursorial lifestyle, walking on two legs and living and running on land.  Evidence supporting this idea includes Hypsilophodons elongate legs and feet bones, stiffened hips and straight tail used to counterbalance the body.

They were likely to be browsing herbivores that foraged near the ground, using their horny beaks and mouths equipped with strong, leaf-shaped cheek teeth to shred vegetation.  Their pointed premaxilla may have been used to break open seeds or even feed on insects and smaller vertebrates, suggesting an omnivorous lifestyle.

Their morphology suggests that the animals were fast runners, using their stiff tail for balance.  Calculations done by Richard Thulborn put their running speeds at about 10 to 20 miles per hour.

Their fossils show that a large number of animals were buried together and suggest that they were herd animals.  Common predators of Hypsilophodon may include the dinosaurs Neovenator and Eotyrannus, as well as the crocodile Goniopholis.

The human story

Hypsilophodon foxii was named after the Reverend William Fox who worked at Brighstone on the Isle of Wight.

William Fox was born in Cumberland.  He arrived on the Isle of Wight in 1862 and took the curate’s position at Brixton, now Brightstone, church.  With easy access to the cliffs and foreshore that made up the south-west coast of the Isle of Wight, he became an avid collector of fossils on the island.

Although he was only an amateur collector, he was famous for discovering new dinosaurs, as well as finding the remains of Hypsilophodon.  He rarely attempted to write about his discoveries, sending most of what he found to more experienced palaeontologists such as Richard Owen and Thomas Huxley.  The work of Fox and many other amateur fossil collectors played, and still plays today, a crucial role in our understanding of ancient life as we know it.

The future

Work to establish the relationship with other dinosaurs of its type continues. The family Hypsilophodontidae (hypsilophodontids being the plural term) refers to the group of ornithopod dinosaurs that are more closely related to Hypsilophodon than to iguanodontians like Iguanodon. The group was originally erected in 1882 by Louis Dollo and has been used in various ways ever since. Charles Stenberg used the name for an assemblage of several ornithopod genera in 1940. Michael Cooper created the group Hypsilophodontia in 1985 that was a higher level taxon including both hypsilophodontids and iguanodontids; however, Paul Sereno used the name as a synonym of Hypsilophodontidae in 1986. Recently, authors use Hypsilophodontidae for the Hypsilophodon group only, due to uncertainties about their relationships with other supposed hypsilophodontids.  Such supposed hypsilophodontids, such as Zephyrosaurus, appear to be significantly different from Hypsilophodon.  Many traits found in basal iguanodontians are also reported in hypsilophodontians.  So after years of re-defining the name, the current consensus is that Hypsilophodontidae refers to a paraphyletic group that is basal within Euornithopoda.  More work needs to be done to see what dinosaurs were actually hypsilophodontids and where their affinities truly lie.

The mystery of the event that resulted in a number of animals dying and being fossilised at one particular location also continues. This is still a debated question regarding Hypsilophodon. How did they all perish and become fossilised? Well, many of the remains found closely together on the Isle of Wight suggest that the animals were buried during a catastrophic event - but there are two conflicting theories. One theory is that the smaller animals in the herd may have become trapped by quicksand, and this is supported by soft-sediment structures within the rock unit. The other theory is that they were buried during a flash flood. Research by Bill Webb, Rob Coram and Mike Cotterill suggests that the silty muds and sandstones formed on a vast, flat plain that was persistently flooded with sediment-heavy rivers that swiftly buried the animals. One of the main forms of evidence supporting this idea is that the limbs of animals trapped by quicksands generally point downwards when they become stuck, which the Hypsilophodon fossils do not show.

Work by Butler and Galton suggests that Hypsilophodon possessed intercostal plates of cartilage but were they present in other basal ornithopods?  If so, why haven't we noticed them before?  They may have been unrecognised by previous workers or the mineralisation of the plates themselves may be dependent on maturity, sex and/or size.  Re-examination of previously described specimens or the discovery of new material may shine light on this.

Produced by

Click here for the University of Portsmouth websiteThis webpage was researched and compiled by Cameron Henderson, a student at the School of Earth and Environmental Science, University of Portsmouth, Burnaby Building, Burnaby Road, Portsmouth, Hampshire PO1 3QL England. 

The work was produced as a result of a research project during 2016.


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