Frequently asked questions about Isle of Wight geology and fossils.
1. What are the rock types on the Island?
They are all sedimentary - muds, clays, limestones and sandstones laid down by water in the forms of rivers, lakes, ponds and seas.
2. Why only sedimentary?
Sedimentary rocks are all that are exposed on the surface. Much of Southern England is similar, but further west, particularly in Cornwall, very hard, old igneous rocks are exposed in the form of Tors.
3. Are there any other older rocks than Cretaceous exposed on the Island?
No. But older rocks lie deep beneath the Cretaceous sequence as proved by deep drilling.
4. Why are the rocks different between South and North on the Island?
All sedimentary rocks were originally deposited horizontally, subsequent movement (folding and faulting) disturbs the layers. This is common in many areas of the Earth’s crust. On the Isle of Wight movement has caused a giant asymmetrical fold, known as the Isle of Wight monocline; in effect the originally horizontal layers have been thrust upwards, revealing very old Wealden beds on the South-West coast, younger white Chalk beds forming the downland, the backbone of the Island (running East to West), and the youngest beds of the Palaeogene and Quaternary on the North coast.
5. How was the Island formed?
Sedimentary rocks were laid down over many millions of years on ancient basement rock now deeply buried beneath the Island. The oldest sedimentary rocks visible on the Island date from about 126 million years ago. At this time sands and muds were being deposited on a river floodplain. Several millions of years later this ancient ‘dinosaur’ floodplain was covered by a shallow sea which gradually deepened until about 100 million years ago when the White Chalk limestone began to form on the seafloor. Millions of years later, uplift of the seafloor exposed the Chalk to erosion. Fresh and brackish water clays and limestones were then deposited. By about 30 Million years ago, the land was again exposed to erosion. 12000 years ago, after the Ice-Age, as ice and snow melted, the sea rose dramatically and cut off the landmass that we know as the British Isles, from continental Europe. By about 6000 years ago, the Isle of Wight was cut off from the English Mainland. Rising sea levels, and constant coastal erosion from Channel storms and winter rains cut away at the Island to the extent of a loss of land of about 1 metre (on average) per year. In several thousands of years there will no longer be an Isle of Wight.
6. Why do we make moulds of fossils?
Some fossils are very rare, even unique or very fragile. This means that a cast reproduced from a mould of the real fossil, can be used for various purposes such as display, without risk of damage to the original.
7. Why are some fossils heavy?
It is all about which minerals replace the original structure of the fossil. Bones still within the body are full of various tissues and fluids such as blood, nerves etc. On death, the soft tissues decay and disappear leaving voids within the bone. During burial the bone absorbs minute particles of minerals, usually brought in by fluctuating levels of groundwater. Eventually, the bone is filled with inorganic minerals such as forms of iron. A common, and very heavy, iron mineral is fools’ gold, iron sulphide (FeS) commonly associated with local wood and dinosaur bones. We also find Barites in our fossils - this is much heavier than iron.
8. Why are there replica bones as well as real fossil bones attached to the skeletons on display?
Very few skeletons are found complete, missing bones are replaced with replicas. Even when there are more real bones they are often very fragile and need to be specially cared for rather than displayed. Very heavy bones are difficult to mount as skeletons. In the Neovenator skeletal display there are many real bones comprising the skeleton; the leg bones are enormously heavy, each femur has a mass of about 25 kg!
9. If I find a fossil where can I get it identified?
Here, at Dinosaur Isle. If you do not live on the Isle of Wight try your local museum or send us a photograph of the fossil, but remember to tell us where you found it.
10. How do fossil fish and shell beds form?
Both fish and shellfish are extremely common animals so their skeletons have very good chances of becoming fossilized on sea floors, lake bottoms and other watery environments where muds are forming. Some shellbeds consist completely of shells with apparently little matrix (mud). These beach-like accumulations can be the result of storms where the shells are washed together and die en-masse.
11. Why do there appear to be more fossils in clays rather than in the Chalk?
Some types of clay are very rich in fossils, others are not. For instance, much of the Formation known as the Atherfield Clay has few fossils, mostly echinoids and bivalves; but within the Atherfield Clay we see thin seams rich in small lobsters and many types of bivalves, gastropods and ammonites. This is also true of the Chalk, which often appears bland and sterile. However, certain levels within the Chalk (known as zones) are very rich, particularly in ammonites, bivalves and echinoids. Ancient seas are similar to modern ones, some seas teemed with life because of warm temperatures, plentiful food supply etc; others were less rich because they were hypersaline, cold etc. Remember that we only ever find a minute fraction of past life, because it was either never fossilized in the first place, or it was destroyed by erosion after burial.
12. How does fools’ gold (iron pyrites) form? And why is it so often associated with fossil wood?
Iron pyrites, fools’ gold, iron sulphide (FeS) forms in putrid or decomposing conditions. We may imagine a pond becoming quite stagnant (putrid) with the decaying carcass of a dinosaur and the trunks of a few rotting trees. As the oxygen within the pond is consumed by bacteria, the pH value of the pond rises and ammonia is generated. The sulphate content of the pond is reduced by bacterial action to produce iron sulphide which crystallizes in and around bones and wood. Fossils containing fools’ gold cause very severe problems for preparators and conservators; firstly the tough crystals and coatings are difficult and sometimes impossible to remove, and secondly, in a humid environment may begin to rust, breaking down the fossil and producing problematical products such as types of acid.
Wood is full of hollow cells which trap the minerals when they the dead tree or plant is buried. Fossil wood can end up thoroughly soaked with iron-sulphide and crumbles away when it dries out.
13. When were the first dinosaurs discovered?
Probably many hundreds of years ago as chance finds whilst digging pits for rock – but they were unrecognized. Robert Plot published a description, in 1677, of the distal end of a femur (probably Megalosaurus) which he thought might belong to an extinct race of giant humans. In 1822, Gideon or Ann Mantell found teeth and bones belonging to a giant animal subsequently identified as Iguanodon, a herbivorous dinosaur. In 1841, Richard Owen identified several finds, Iguanodon bones amongst them, as belonging to a new group of reptiles which he named DINOSAURIA (terrible lizards).
14. What are bones made of?
Mostly of the mineral calcium phosphate.
15. What are fossil bones made of?
Originally mostly calcium phosphate – over time the organic content is replaced by inorganic minerals such as calcite, barites and iron sulphide.
16. How quickly (or slowly) does it take for a fossil to be formed?
Sometimes very quickly, sometimes very slowly. Imagine 125 Million years ago, when dinosaurs were wandering about on a land mass which we now call the Isle of Wight; all around is a flat marshy land, dissected by rivers, streams and ponds. Muddy areas surround the waterways, where dinosaurs can trample and roll around leaving body impressions and lots of footprints. Occasionally a dinosaur dies in the mud, or is swept in by a flood. After the flesh decays, the bones begin to sink into the mud. Very quickly (sometimes in a matter of weeks) bacteria aided by complex chemical conditions allow the replacement of bone with black sulphurous deposits, (pick up a rock which has been lying on the beach for a few weeks and look for the black staining underneath). This is the beginning of the fossilization process. Years later, after layers of mud and sand have piled on top of the dinosaur bones, they may crack under pressure. The cracks allow the formation of water-borne minerals such as calcite to invade and fill voids in the bone structure. The fossils in this museum and those you find are on a long and changing journey, if you took them back to the beach and buried them, over years they would change with the invasion of other types of minerals depending on the environment. Nothing remains the same (unchanged) for ever.
17. Is Tyrannosaurus rex found on the Island?
No. Tyrannosaurus Rex (T-Rex) is only found in North America, but it has some close cousins in the Gobi Desert. T-Rex lived during the time of the Late Cretaceous. During this time global sea levels were very high. Most of North-West Europe and England were under deep water (the Chalk Sea) so there was no land for T-Rex, or other dinosaurs to live on. Large areas of North America were above water so this is where we find their fossil remains. The Island does have an early member of the Tyrannosaurid family called Eotyrannus.
The skull of Eotyrannus is only 50 centimetres long, but a skull from T-rex can be 160 centimetres long. Over millions of years some of these predators grew to truly enormous sizes.
18. Is Velociraptor found here?
No. Velociraptor is a late Cretaceous dinosaur, and is found only in the Gobi Desert, Outer Mongolia. It grew to about 1.8 metres in length. Velociraptor was made famous by the film “Jurassic Park”.
19. Why are there so many dinosaurs found on the Isle of Wight?
The environment was just right to support large herds of plant-eating (herbivorous) dinosaurs. It was warm for most of the year. Food, in the form of plants, and freshwater from the rivers was widely available. Over 20 types of dinosaur have been identified to date and there are many more types of reptiles, other animals, and plants preserved as fossils.
The dinosaurs migrated along a long river valley that ran across the southern half of the Island. The river started somewhere near Devon, it flowed east across the Isle of Wight and continued out into what is now the eastern Channel. Many herbivorous dinosaurs travelled together, much as modern wild herds do, as protection against the meat-eating (carnivorous) dinosaurs that followed them. The carnivores picked off the weak, the sick, old and young, and devoured any carcasses that were lying about. There would have been many skeletons, and scattered bones, lying about.
The ancient environment that is exposed on the Island supported dinosaurs for over 10 million years; so lots of animals and lots of time means lots of potential fossils. Conditions have also been right to preserve and store the fossils so that we can find them now. Bones started their fossilization process in large ponds of oxygen-poor mud which ensured that much of the fine detail was preserved.
The ground on the southern half of the Island had also been sinking throughout the Permian, Triassic and Jurassic Periods and this continued through much of the Cretaceous. River muds and sands accumulated in the sinking hollow, and this meant that the bones were stored safely away from erosion.
After tens of millions of years (during the Eocene and later) the ground was pushed up again (as a result of the Alps forming) and the bones (now fossils) were exposed at the surface.
Continuing coastal erosion and careful collecting have resulted in the wealth of fossil finds we have today.
20. How many types of dinosaurs are found on the Island?
There are about 20 properly established Island dinosaurs. The best known are two species of Iguanodon, large herbivores; two unique carnivores, Neovenator and Eotyrannus; the small bipedal herbivore Hypsilophodon; the armoured Polacanthus and a large brachiosaurid. Unfortunately, all of the many names invented for the other Island dinosaurs are based on a few fragments, often upon a single bone!
There are many hundreds of types of dinosaurs to be found globally, and a new type is found every few years. The wide range of dinosaur types found on the Island show that the environment must have been just right to support such a diverse eco-system for many millions of years.
21. What are the biggest dinosaur bones you have?
The biggest bones must come from the largest type of dinosaur to have existed, the long-necked sauropods. The upper arm and leg bones (humerus and femur) from the Barnes High sauropod are over a metre long. In order to support the weight of the long neck the shoulders on this animal are enormous. A single shoulder blade (scapula) is over 120 centimetres long. We also have a single neck vertebra from another sauropod that is 75 centimetres long, and if we had the rest of it would possibly be from the largest dinosaur ever found in this country.
22. Where can I can find out more about the geology of the Island?
We have published an online document called the Isle of Wight Local Geodiversity Action Plan (IWLGAP). It contains a summary of the evolution of the Isle of Wight's geology, and lists some of the more important areas of the Island. You can find this document by visiting our LGAP webpage.
23. I have found a large fossil ammonite. Why is it well preserved on one side and just hard sand on the other?
Ammonites are extinct marine creatures related to today's Nautilus. When the ammonite dies one of two things can happen to it. It is either ripped to pieces by a large marine reptile, or another ammonite, leaving a shower of shell fragments and organic remains to sink to the sea floor; or it can slowly settle onto the bottom where the soft parts are eaten as it is slowly buried in mud or sand.
For most ammonites that are preseved as fossils the inner chambers gradually fill with sand or mud and the original shape is preserved.
Over time the upper part of the shell and the exposed infill is eroded away by sand carried along in water currents. The lower part underneath (that is buried in the sea-floor) is preserved. This is what happens to many ancient wooden shipwrecks, where the masts and decks rot away but the hull and keel is preserved. A classic example of this is the Mary Rose, King Henry the Eighth's prize warship which sank in the Solent almost 500 years ago.
Once the hardened fossil has fallen out of the cliff, it can often be seen that it has a 'best side'. If the ammonite had big ridges on it's shell then this can help to ensure the water currents didn't move it about too much after it died. These bigger ammonites often show this kind of assymetrical preservation.
24. Are pterosaurs and pliosaurs dinosaurs?
No. definitely not! Dinosaurs were defined scientifically as a specific group of reptiles that walked on land, with their femurs (upper leg bones) hanging vertically down.
Creatures like crocodiles, pterosaurs and pliosaurs were also reptiles - but they don't qualify as dinosaurs because, for example, in the case of crocodiles the legs go out sideways from their hips and then turn down; pterosaurs aren't predominantly land animals (they fly) and their hind legs aren't like those of dinosaurs; and pliosaurs don't have legs like land animals, they have flippers and swim. Although some dinosaurs might have been able to wade across small rivers or lakes they are mainly land animals.
25. What is coprolite?
Did you know that it isn’t just the hard parts of animals and plants that get fossilized? We get used to finding fossil bones, teeth, scales; and parts of wooden tree trunks and seed cones, but look carefully on the beaches around the Island (and be careful what you pick up) and you may find ‘coprolite’.
Dinosaur Isle has a collection of coprolites from various carnivorous animals. They can tell us about what the animal was eating, and perhaps even what parasites it had. What is ‘coprolite’? Well it wasn’t always hard. And you wouldn’t want to pick it up when it was new. Today, many millions of years later, it has turned to rock. To be tasteful let us just call it ‘fossil poo’!! You can sometimes even see the marks where it was squeezed out!
| || |
Dinosaurs Homepage Iguanodon Neovenator salerii Eotyrannus lengi Hypsilophodon foxi Valdosaurus Sauropodomorpha Polacanthus Baryonyx
|Dinosaur Isle, |
Isle of Wight
Tel: +44 (0)1983 404344
| || || |