Wessex Formation



The Isle of Wight is one of the best places to see some of England's finest and most prosperous dinosaur fossil beds. Small though the island is, the contributions to paleontology in England are immense, with fossils being found here since the 19th Century.

Paleontology as a field originated in England and the fossils from Wight were causing a stir among scientists at the time. One of the more famous Isle of Wight fossil beds is the Wessex Formation, a part of the extensive Wealden Supergroup. The Weald covers a huge range, from the beginning of the Cretaceous onward, ending during the early Aptian Stage. Much of the Weald consists of alternating beds of clay and sand that were put down between 140 and 125 million years ago.

The Setting

These beds represent a seeming time of plenty for the native animals, with coastal lagoons, braided rivers and freshwater floodplains. It is the kind of environment that we have associated large dinosaurs with for centuries and the Wessex Formation delivers on that premise. There were also periods of drought, and short winter seasons and long summers where temperatures were as high as 30 degrees Celsius.

The Wessex covers a span ranging from 130 to 126 million years ago, during the Barremian Stage of the Early Cretaceous. At the time, the landscape was very different, with extensive horsetail beds by the riversides. These were somewhat akin to the reed-beds of our time, while plants such as ferns, cycads, conifers and early flowering plants may have been common further inland. The uplands in particular might have been more of a wooded setting rather than a river system. In the water were many fish and freshwater snails which were preyed on by numerous other animals.


Among the most bewildering is one of the smallest stem-crocodiles ever discovered. This was the so-called 'button-toothed croc', the Koumpiodontosuchus. It and its relatives were oddballs measuring 60 centimeters long. It was small enough to hunt for the snails and other small freshwater mollusks that grazed on algae and rotting vegetation in the Wessex rivers. Koumpiodontosuchus is known from remarkable remains, including a good skull that shows off its extremely specialized dentition. Other crocodylomorphs in the area were much more standard in terms of size and habits.


The ornithocheirid Caulkicephalus is one of the larger pterosaurs from the formation. It was a hunter that picked fish from just below the surface with its needle-sharp teeth. This sizable pterosaur was not the only flying reptile here though. It coexisted with the bulky Istiodactylus.

This animal was more comfortable on land than Caulkicephalus was, Istiodactylus was also much stronger in build, and had a broad muzzle and strong teeth suited for cutting and tearing flesh. Pterosaur researcher Mark Witton suggested in 2012 that these pterosaurs may have been scavengers.


The biggest carnivores in the Wessex though, were the dinosaurs. One of the most iconic British dinosaurs is Baryonyx, also one of the most completely known members of its family. Baryonyx was a spinosaurid, a relative of the more famous Spinosaurus but differed in its lack of a sail, longer legs and other anatomical details. Fossils of this animal were discovered in a clay pit in Surrey by an amateur fossil hunter in 1983.

One of the ,most captivating remains from Baryonyx was a huge, curved claw. After its naming by Angela Milner and Alan Charig in 1986, it became a veritable celebrity, appearing in many popular books. It was, after all, the first conclusively known fish-eating dinosaur. Soon, Spinosaurus started to overtake it in celeb status. Baryonyx though, was still the largest theropod from Britain, growing as much as 10 meters in length. It used its massive claws to help it hook large fish in lakes and rivers while its gharial-like teeth dispatched the victims. Fossils of the fish Scheenstia have been found in the stomach of Baryonyx.

Second on the list was Neovenator, a more typical and recognizable theropod that spent more time on land than in the water. It was a carnosaur, a distant relative of the famous Allosaurus from Jurassic North America. It was marginally similar in terms of size too, at around 7.5 meters and weighing between 1 and 2 tons. It was also probably the top predator of the Wessex, feeding on a wide variety of herbivorous dinosaurs and other animals.

Lower on the list of big predators was the early tyrannosauroid named Eotyrannus. It was far from being a big and powerful predator, instead being the jackal or coyote of its time. It was a speedy, medium-sized theropod roughly 5 meters in length and probably fed on smaller dinosaurs. Eotyrannus is known from rather complete fossils discovered by fossil hunter Gavin Leng, and was named in 2001 by Hutt and colleagues.


Perhaps the most famous and still taxonomically confused of all British dinosaurs is Iguanodon. It was one of the earliest dinosaurs ever known, with its remains being described scientifically in 1825 by Gideon Mantell. This paleontological classic was originally included in Sir Richard Owen's original Dinosauria and has since undergone a number of revisions over the past 194 years.

We all remember how it was first reconstructed as a plodding quadruped, then as a stiff-backed erect biped and finally as something in between. Iguanodon and its kin were able to walk comfortably on all fours yet could still rear up and run on two legs at a good speed. Its most famous features are its massive thumb spikes, the purposed of which have ranged from manipulating tool to defense mechanism. It is possible that Iguanodon used this arguably powerful melee weapon on members of its own kind rather than just on its predators.

These changes are undoubtedly important but another alteration has been afoot for a while, and that is the whittling down of species. Iguanodon was once the most successful and widespread dinosaur in the world, with fossils known from all over Europe. Now though, only two species are regarded as valid: The big 10-12-meter species Iguanodon bernissartensis and the Spanish I. galvensis.

Not even all the Weald specimens are regarded as being part of Iguanodon anymore. Rather the mid 2000's were full of splits. The oldest English specimens from the end of the Jurassic were placed in the genus Owenodon. These specimens come from the Purbeck Limestone. The Wessex contains I. bernissartensis as well as the smaller Mantellisaurus. The latter can also be found in the younger Vectis Formation. The slightly earlier Wadhurst Formation contains the bulky Bariliun, the small Hypselospinus and the medium-sized Sellacoxa. All in all, the story of Iguanodon is long and convoluted, and for now at least these is no more confusion.


As for armored dinosaurs, we gave Polacanthus, a stout and powerfully-built 'walking coffee table' armed to the teeth with bony spines. This medium-sized herbivore was an early armored dinosaur, not as advanced as more famous animals like Ankylosaurus and Edmontonia. It too has been known since the 1800s.


Sauropods are not the best-known dinosaurs from the Wessex Formation. There are remains from rebbachisaurs ,a relative of the more famous North African Nigersaurus and Rebbachisaurus. These were somewhat small for sauropods, nowhere near as big as Britain's supposedly biggest dinosaur.

This mysterious creature was named and described by known paleontologist Darren Naish, and is known by the informal name of "Angloposeidon". It is not properly described, and is known only from a single cervical or neck vertebra. It is a possible brachiosaur, estimated at somewhere between 20 and 25 meters long.