The dinosaurs of the Isle of Wight

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Simon Clabby (UK)

There has been much written about the dinosaurs of the Isle of Wight over the years. For example, Gideon Mantell, who discovered Iguanodon in 1821, wrote a book on the geology in 1847, in which he refers to its fossil fauna. However, like all sciences, palaeontological research does not stand still. Every year, our knowledge about dinosaurs changes as new discoveries are made. This is true even of the Isle of Wight, which, since the 1980s, has experienced a sudden upsurge in research, making many books on the subject now out of date.

The first dinosaur discoveries took place in antiquity, with local stories of “stone horses” (presumably Iguanodon, due to its horse-like skull) being found in the cliffs. However, the first scientific discoveries took place in 1829, when William Buckland (describer of Megalosaurus) described some Iguanodon material from Yaverland. The mid 1800s was a time of massive interest in dinosaur research, with the Rev. William Fox, curate at Brighstone village (not far from the fossil-rich cliffs at Brighstone bay) apparently neglecting his duties to look for fossils. In fact, he managed to discover four new species during his tenure at Brighstone.

Fig. 1. Brighstone Bay.

There was a bit of a lull in the early twentieth century, with nothing new being discovered until the 1970s. However, since then, at least three new species have been described, and a further seven previously known species being reassigned to new taxa.

The dinosaurs of the Isle of Wight almost all come from the Wessex Formation, a group of rocks that date from an age known as the Barremian (125 to 130 million years ago), during the Early Cretaceous period. During this time, the Isle of Wight was much nearer the equator than it is today, and had a warmer climate. The Wessex Basin, within which the Isle of Wight is located, was a large floodplain, surrounded by conifer forest-covered hills.

Fig. 2. In the top left, we have a Baryonyx surveying the landscape while a Caulkicephalus (the pterosaur) snags a fish, the bottom right. At the middle-bottom of the image, a Goniopholis is enjoying a fish dinner while other Goniopholis slink around the water margins. The bottom right, a small feathered theropod is chasing salamanders, while the armoured Polocanthus walks away from the water edge in the middle right. In the middle background, a herd of Iguanodon is moving into view, an image inspired by the abundant Iguanodon footprints found throughout the Wessex Basin. (Illustration by Mark Witton.)

The plain was seasonally flooded, and would vary from near desert conditions to wetlands. However, there were plenty of ferns and tree ferns to sustain the herbivore population. The landscape was covered in shallow, anoxic (oxygen-free) puddles. In addition, there was the occasional lake that would attract plenty of Iguanodon herds to its waters, as well as providing a home for turtles, crocodiles and fish, together with bivalves and other invertebrates. It was this seasonal flooding that allowed so many different genera to be preserved as fossils.

Dinosaurs can be found at several sites on the Isle of Wight. Firstly, there is Yaverland, near Sandown, where several dinosaur species have been found, as well as the occasional footprint.

Fig. 3. Yaverland is one of the most popular locations on the Isle of Wight for dinosaur remains, being the locality of many famous finds.

However, the best site to find dinosaurs is on the southwest coast, between Cowleaze Chine and Hanover point. This stretch of coastline is one of the most productive for dinosaur remains in the UK, and maybe even the world – over 20 species can be found here, many of which are unique to the island. Whether this is due to the depositional conditions, high productivity or just the large fossil collecting community on the Isle of Wight, it is impossible to say, but it may be a combination of all these factors.

Fig. 4. Hanover Point.

Ornithopod dinosaurs

Starting with the Ornithopod dinosaurs, the most common dinosaur is Iguanodon, a large, herbivorous dinosaur, reaching 10m in length. Iguanodon is probably the most famous of the Isle of Wight’s dinosaurs and is known from all over the world. Iguanodon would have been a high-browser, rearing up on its hind legs to feed on high branches of tree-ferns and conifers, both of which have been found in the Isle of Wight fossil record.

Recent taxonomy work of Iguanodon
Recent work on the taxonomy of Iguanodon has shown that the Isle of Wight’s Iguanodon specimens belong to three distinct genera – Iguanodon (Iguanodon bernissartensis), Mantellisaurus (previously Iguanodon atherfieldensis) and Dollodon (based on undescribed Iguanodon material): Iguanodon (iguana tooth) is the largest of the three, with the large thumb spike the iguanodontids are famous for, and a robust, short skull with a toothless beak.
Mantellisaurus (Mantell’s reptile, after Gideon Mantell) is smaller, about 7m in length, and more gracile, with a reduced thumb spike and a longer skull, with higher neural spines.
Dollodon (Dollo’s tooth, after Louis Dollo, who did a lot of work on the Belgian Iguanodon specimens that corrected previous restorations) is poorly known on the island, but is known to have had a long snout and high neural spines possibly forming a small sail along the back. There is now some debate as to whether Iguanodon is actually an iguanodontid. However, until that research is published, it remains as such.
Fig. 5. Iguanodon bernissartensis, caudal vertebra. (Photo by Paul de la Salle.)

Closely related to the iguanodontids is Valdosaurus (Weald reptile), a dryosaurid dinosaur about 4m long, with a toothless beak and slender limbs. It would have lived a similar lifestyle to a gazelle, browsing on ferns and bushes. Valdosaurus is also known from Africa, suggesting that Europe and Africa were either connected or had only recently separated.

The smallest ornithopod is Hypsilophodon (high-ridged tooth) that was about 2m in length and which can be found in large numbers in a layer known as the Hypsilophodon beds. This layer is believed to have been laid down by sudden flooding, washing the poor Hypsilophodon away. An unusual aspect of the Hypsilophodon beds it that most of the specimens are juveniles, and a few seem to have been preserved in a resting position. There is also anecdotal evidence for them being found in pairs. The large numbers found suggests Hypsilophodon lived in communes, moving through areas like sheep, grazing on ferns and cycads, and possibly even small mammals. Hypsilophodon had a short skull, with a toothed beak, and highly developed muscle attachments in the hind legs. This suggests that it could manage quite a good speed, enabling it to get away from predators.

Those of you who know about dinosaurs may be wondering about a few missing dinosaurs from this list.Vectisaurus, which was believed to have been a small ornithopod, is actually Iguanodon (possibly even Mantellisaurus) and, as for Yaverlandia, the ‘earliest known pachycephalosaur’, we’ll be seeing it again later …

Thyreophoran (armoured) dinosaurs

It was not just ornithopods grazing on the Isle of Wight. There was an ankylosaur too – Polacanthus. Polacanthus (many-spined) has occasionally been attributed to the nodosaurids, due to its club-less tail. However, comparisons with other similar genera, such as Gastonia from the US, show it would have had a more squared off, triangular head, more like ankylosaurids than the narrow-snouted nodosaurs. There have even been suggestions of placing Polacanthus in its own group, the polacanthids, due to its unique nature. Polacanthus was about 4m long, with large spines along the back and shoulders, and a large bony shield across the sacrum (a triangular bone at the base of the spine).

A braincase found near Brighstone bay and allocated to Polacanthus based on similarities to Gastonia, has shown that Polacanthus was more aware than most ankylosaurs. This suggests that it had a more active method of avoiding predators. The positioning of the spines on the shoulders hints that Polacanthus may have used them to “shoulder-barge” any threat, if a display of the large dorsal spikes failed to put them off. The relatively unprotected flanks and hind legs discount any suggestion of Polacanthus using the “duck and cover” method favoured by children’s books for the last 50 years. It would have been a low browser, possibly following the Iguanodon herds, as there are Iguanodon and Polacanthus footcasts found together at Hanover point.

Finally, there is a stegosaur, tentatively attributed to Regnosaurus (Regni reptile, after the Romano-British Regni tribe of West Sussex), due to diagnostic features in the single specimen (a partial pelvis) that are unique to huayangosaurid stegosaurs. Little is known of Regnosaurus, other than it was a huayangosaurid. However, it can be inferred that it was a low browser, with dorsal spines and solitary spines on the shoulders.

Sauropod dinosaurs

Sauropods seem to have been quite diverse on the Isle of Wight, leading some to speculate that they were just passing through. However, it has been suggested that there was suitable vegetation for them to thrive there.

The largest is MIWG 7306, which is the specimen number of a single neck vertebra belonging to a brachiosaurid. This particular brachiosaur was about 20m long, making it the largest dinosaur known in Europe, and is comparable in size to Brachiosaurus from Africa and Sauroposeidon from the US. MIWG 7306 would have been a high browser, biting off branches from conifer trees and grinding them up in the gut with gastroliths from the nearby cliffs.

Fig. 5. MIWG 7306. (Illustration by Mark Witton.)

MIWG 7306 was not the only brachiosaur. There was also Eucamerotus (well chambered) at 15m long, Ornithopsis (bird-like) at 15m to 18m and Pelorosaurus (Peloros’s reptile, after the Tessalian name for Saturn) at 15m. However, Eucamerotus and Ornithopsis are both known from vertebrae, none of which are exactly the same bone. Therefore, it is possible that they could be the same genus, or even the same species. Work that is still ongoing with the Barnes High Sauropod, being conducted by experts from both Dinosaur Farm Museum and Dinosaur Isle, should help to sort out this taxonomic mess. The Barnes High Sauropod is interesting in that it appears to have fallen into a natural trap, by wandering into mud and getting stuck. This would explain the near completeness of the skeleton, although the skull is missing.

Other sauropods found on the Isle of Wight include the titanosaurs, Iuticosaurus, and Pleurocoelus. Luticosaurus (Jute reptile, after the Jute tribe that lived in Kent, Sussex and the Isle of Wight) was between 15 to 20m long, and is known from a single caudal vertebra (titanosaur vertebrae are convex at the rear and concave at the front, and the neural process is towards the rear, making identification easier).

Pleurocoelus (hollow sided) is known from a single, peg-like tooth, which, by comparison with other titanosaurs, shows it to be relatively small, just 8m long.

There were also a few problematic sauropods. Chondrosteosaurus (cartilaginous-boned reptile) was once attributed to the camarasaurs, but the features used to diagnose it as such have proved to be more common among sauropods than previously thought. It was 18m long.

Oplosaurus (hoplon lizard, after the ancient Greek shield), which was probably between 20 to 25m long and is known from a single tooth, is considered by the majority to be camarasaurid in nature. However, there are some who believe it to be indeterminate.

Finally, we have a few undescribed sauropods. There are at least two diplodocids and a rebbachisaurid, known from isolated fragments.

Theropod dinosaurs

And finally, we get to the theropods …

The largest described theropod is Baryonyx (heavy claw), a spinosauroid better known from Sussex. It is presumed to be a piscivore, due to its long, crocodilian snout, conical teeth and the presence of acid-etched fish scales in the gut area. There were also juvenile Iguanodon bones found in the gut or a Baryonyx specimen found in Sussex, suggesting it at least scavenged on this herbivore. However, Baryonyx is most famous for the large claw on its first digit, which may have been used to catch fish by “gaffing” them in the manner of a bear. Analysis of Baryonyx material from the Isle of Wight has shown that it is probably the same genus as Suchomimus, a larger spinosauroid from Africa. (There may also be another spinosauroid on the Isle of Wight, known from teeth previously attributed to the crocodilian, Suchosaurus, although there is still work to be done on these.)

Fig. 6. Neovenator, cervical vertebra. (Photo by Paul de la Salle.)

If you consider that Baryonyx was a scavenging piscivore, the major predator found on the Isle of Wight was Neovenator (new hunter). This was an 8m-long carcharodontosaur, similar to allosaurs. It had a distinctive, puffin-beak shaped snout, and would have preyed on Iguanodon and, possibly, the occasional smaller sauropod. There is also a larger, undescribed theropod, known only from a few hand bones, but they are non-diagnostic and so cannot yet be attributed to any known group.

Fig. 7. Neovenator attacking a Hypsilophodon. (Illustration by Mark Witton.)

The Isle of Wight’s most famous theropod is Eotyrannus (early tyrant), at 4m long. While it is not the biggest, it is important as it is one of the earliest tyrannosauroids. It was found in association with some Valdosaurus bones, which could suggest that Valdosaurus was at least part of Eotyrannus’ diet.

Fig. 8. Eotyrannus tibia. (Photo by Paul de la Salle.)

Thecocoelurus (sheath hollow form) was an oviraptorsaur, which is uncommon in Europe. At 7m in length, it is also unusually large. Thecocoelurus is only known from a single partial vertebra, which fortunately has enough diagnostic features to allow its attribution to the oviraptorsauria, although, for a while, it was considered by some to be a therizinosaur. As almost all oviraptorsaurs were toothless, it is possible that Thecocoelurus was too, although this does not preclude it from a carnivore lifestyle.

Aristosuchus (superior crocodile) was, until recently, also an unusually large example of its taxon, in this case the compsognathids, best known from the tiny Compsognathus from Bavaria. Presumably, Aristosuchus would have eaten lizards and small mammals.

Calamosaurus (reed reptile) was a coelurosaur, which is, in many cases, a very vague term for a small theropod. Work is being done on the existing specimens, but nothing has been published yet.

Calamospondylus (reed vertebrae) is an indeterminate theropod, known from a sacrum that was described once then lost, without being photographed or drawn, so no more information is forthcoming sadly. It was once thought to have been a synonym of Calamosaurus, but examination of the Calamosaurus material shows it to be something else.

Ornithodesmus (bird link) has had a colourful past. Originally classed as a pterosaur, in 1992 it was discovered that the type specimen, a sacrum, was not from a pterosaur, but from a theropod dinosaur, specifically a troodontid However, later examination linked it to the dromaeosauridae. All the pterosaur material attributed to Ornithodesmus was assigned to a new taxon, Istiodactylus. Another dromaeosaur was the large velociraptorine that has been identified by some teeth found by sieving sediments. The sizes of the teeth suggest a full length of about 6m.

Finally, there is a reappearance by Yaverlandia (from Yaverland). Originally, this was considered to be a pachycephalosaur, based on a slight thickening of the frontals. However, further examination in the last few years has shown it to have theropod affinities. The answer to the question, “Which particular type of theropod”, I’m afraid, will have to wait until it’s published.

Current work on the fauna of the Wessex Formation is ongoing, with scientists sieving through tonnes of clay looking for microscopic bones. By these means, they have uncovered teeth and even fragments of eggshell and, with fossil hunters scouring the beaches every day, there is bound to be more discoveries to come in the future.

Further reading

Dinosaurs of the Isle of Wight: Guide No 10, edited by David M Martill and Darren Naish, The Palaeontological Association, London (2001), 433 pages (paperback), ISBN: 0901702722

Dinosaurs of the British Isles, by Dean R Lomax and Nobumichi Tamura, Siri Scientific Press, Manchester (2014), 414 pages (paperback), ISBN: 978-0-9574530-5-0

Isle of Wight: Landscape and Geology, by John Downes,‎ The Crowood Press Ltd (2021), 112 pages (paperback), ISBN: 978-1785008924

For more information, check out these websites:
DinoWight – The Dinosaurs of the Isle of Wight – the most complete guide to the Isle of Wight’s dinosaurs online.
Dinosaur Isle, the big dinosaur museum in Sandown.
Dinosaur Farm Museum, close to the fossil beaches and loads of fossils on show.
Tetrapod zoology – updated daily, sometimes has info on Wealden dinosaurs, but when it does it is very detailed.

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