Trilobite

Fantastic fossils

Discover some of the fascinating fossils you can find around Britain, what they look like and where to look for them. What do they tell you about how Britain has changed?

Ammonites, Asteroceras and Promicroceras, found near Yeovil in Somerset.

Ammonites

Ammonites are related to the squids and octopuses you can see today, but they're all extinct - they died out at the same time as dinosaurs.

Their shell is usually a flat spiral shape. It is made up of chambers, like little rooms within the shell, connected by a tube. The animal only lived in one of these chambers and used the other spaces to help it float. Some ammonites were tiny, others as big as a man.

The image above shows ammonites, Asteroceras and Promicroceras, found near Yeovil in Somerset. Notice their distinctive coiled shells.

Because ammonites lived in the sea, if you find an ammonite fossil in a rock, you know that millions of years ago the spot where you're standing used to be totally covered by the ocean.

Good places to find ammonite fossils: Lyme Regis in Dorset

Age of rocks: about 200 to 65 million years old (Jurassic and Cretaceous Period)

Trilobite, Dalmanites myops

Trilobites

These strange-looking creatures lived hundreds of millions of years ago. They are relatives of crabs and lived in the sea. Some swam, while others walked on the sea floor. By 250 million years ago they had all disappeared.

Trilobites were many different shapes and sizes. Their bodies had 3 main parts - a head, body and tail. And they had a hard cover on their back. This is usually what we are looking at when we find a trilobite fossil.

The image above shows a trilobite, Dalmanites myops, found in 420-million-year-old limestone rock at Dudley in Worcestershire.

We know that many trilobites could roll up, like woodlice can, as fossils often show them in this position.

Good places to find trilobite fossils: Devon, Wales, northern England and southern Scotland. Two very famous sites are Wren's Nest in Dudley, and Girvan in Scotland.

Age of rocks: 540 to 250 million years old (Palaeozoic Era)

Piece of rock containing a single shell of the bivalve Aviculpectin planoradiatus.

Bivalves

Bivalves are soft-bodied animals that have 2 shells, known as valves. Their shells are usually mirror images of each other.

The image above shows a piece of rock containing a single shell of the bivalve Aviculpectin planoradiatus. This fossil is unusual because you can still see the shell's original V-shaped markings.

Bivalves still live in the sea and in freshwater around the world. Some dig burrows in sand or mud, others just lie on the surface, and some attach to a hard surface. Oysters and cockles are probably the most well-known examples alive today.

The oldest bivalve fossils are over 500 million years old. But they are much more common in younger rocks. Sometimes there are so many fossil bivalves that they form whole layers of rock.

Good places to find bivalve fossils: throughout southern, eastern and northern England, South Wales and southern Scotland

Age of rocks: 510 million years old and younger (Palaeozoic Era onwards)

Top and bottom views of the brachiopod Cyclothyris difformis

Brachiopods

Brachiopods live in the sea, usually attached to a hard surface.

There aren't many different kinds of brachiopod around today, but there used to be, so there are lots for you to find and identify. They are very common fossils in rocks over 65 million years old.

Brachiopods look very similar to bivalves, as they also have 2 shells. The best way to tell the difference is to compare the size and shape of the 2 shells. In brachiopods one shell is usually bigger than the other, and the larger shell has a small hole at the top.

The image above shows top and bottom views of the brachiopod Cyclothyris difformis. This 3cm-long fossil was found in Devon.

Good places to find brachiopod fossils: all over southern, eastern and northern England, Wales and southern Scotland

Age of rocks: 540 to 65 million years old (Palaeozoic and Mesozoic Eras)

A piece of flint broken open to reveal the fossil sponge Ventriculites inside.

Sponges

Sponges are ancient animals that mostly live in the sea. They have a very simple body structure made up of groups, or colonies, of cells.

You can find fossil sponges on beaches where most of the pebbles are made of flint. Look out for flint pebbles with patterns of holes in them - these are usually the fossilised remains. Often you can see the whole shape of the colony.

The image above shows a piece of flint broken open to reveal the fossil sponge Ventriculites inside.

Although sponges have soft bodies, they fossilise very well because they are made up of tiny pieces of calcium or silica joined together. When you pick up a piece of flint you are touching the recycled remains of the silica that the sponge was built from.

Good places to find fossil sponges: pebbly beaches in southern and eastern England

Age of rocks: 145 to 65 million years old (Cretaceous Period)

Glossary - what does that word mean?

Calcium - the substance that makes our bones and teeth strong. Other animals also use it to make their hard parts.

Flint - a rock that sometimes contains fossils of animals or plants that lived in the sea. Flint is usually dark grey or brown but it often occurs in round lumps with a thin, white outer layer.

Silica - a very hard substance. It's what sand is usually made of, and some living things use it in their hard parts.

A common heart-shaped sea urchin, Micraster coranguinum.

Sea urchins

Sea urchins are related to starfish. They live in the sea, either buried in sediment such as mud or sand on the sea floor, or on top of it.

Sea urchins are often quite round, and about the size of an apple. They can also be heart-shaped or a flat disc.

The image above shows a common heart-shaped sea urchin, Micraster coranguinum.

Their shell is known as a test. When the animal is alive, the test is covered in many sharp needle-like spines. When it dies, the spines fall off, so you won't often find them as part of the fossil, but you can see the holes where they used to be attached.

If you look in chalk rock you might find lumps of flint that have sea urchin fossils in them. And when you are on a beach keep a look out for a rounded pebble with a starfish pattern on it - you might get lucky.

Good places to find sea urchin fossils: pebbly beaches in southern and eastern England

Age of rocks: 200 to 65 million years old (Jurassic and Cretaceous Periods)

Glossary - what does that word mean?

Chalk - a white rock formed from the hard body parts of tiny creatures that died and sank to the bottom of the ocean 100 to 65 million years ago. The famous White Cliffs of Dover in the UK are made of chalk.

Flint - a rock that sometimes contains fossils of animals or plants that lived in the sea. Flint is usually dark grey or brown but it often occurs in round lumps with a thin, white outer layer.

A collection of fossil teeth from the sand tiger shark

Shark teeth

A shark grows and loses a lot of teeth during its life. This means that in places where shark's teeth are found as fossils, they are often extremely common.

The main part of the tooth is usually sharp and pointed, ideal for piercing the flesh of its prey, and it's attached to a banana-shaped root.

The image above shows a collection of fossil teeth from the sand tiger shark, Odontaspis robusta, found in Kent.

Sharks have been around for a very long time - the oldest teeth discovered are about 400 million years old. But fossils of whole sharks are rare. This is because their skeletons are made of cartilage, which is much softer than bone and rarely becomes fossilised.

Good places to find shark teeth fossils: Sheppey in Kent, and Bracklesham Bay in Sussex

Age of rocks: 56 to 37 million years old (Eocene Epoch)

A fossil of part of the backbone of Liopleurodon.

Bones of dinosaurs and other reptiles

Dinosaurs are probably the most famous prehistoric animal. At the same time as they were walking about on land, other enormous reptiles were living in the sea. But around 65 million years ago, dinosaurs and most aquatic reptiles died out. Scientists are still trying to find out why.

Because of where dinosaurs lived, their bones are usually found in rocks that formed on land. The bones are usually black or brown and you can see a honeycomb structure on the inside of broken ones.

The vertebrae (parts of the backbone) of aquatic reptiles such as ichthyosaurs and plesiosaurs are disc-shaped. But beware: pieces of flint can often look like bones.

The image above shows a fossil of part of the backbone of Liopleurodon. This reptile lived in the sea and was as long as a bus.

Good places to find dinosaur bones: Isle of Wight. The best beaches to try are Yaverland and Compton Bay.

Look in rocks aged: 250 to 65 million years old (Triassic, Jurassic and Cretaceous Periods)

Good places to find aquatic reptile fossils: Lyme Regis and Charmouth in Dorset

Age of rocks: 200 to 145 million years old (Jurassic Period)

Glossary - what does that word mean?

Flint - a rock that sometimes contains fossils of animals or plants that lived in the sea. Flint is usually dark grey or brown but it often occurs in round lumps with a thin, white outer layer.