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 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 person.
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 underwater.
Good places to find ammonite fossils: Lyme Regis in Dorset and Runswick Bay in Yorkshire
Common in rocks aged: about 201 to 66 million years old (Jurassic and Cretaceous periods)
These strange-looking creatures lived hundreds of millions of years ago. They are distant relatives of crabs and lived in the sea. Some swam, while others walked on the sea floor. By 251 million years ago they had all disappeared.
Trilobites were many different shapes and sizes. Their bodies had three main parts - a head, body and tail. They had a hard cover on their back. This is usually what we are looking at when we find a trilobite fossil.
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: Torquay in Devon, Marloes Sands in Wales and Coniston in Cumbria. Two very famous sites are Wren's Nest in Dudley and Girvan in Scotland.
Common in rocks aged: 485 to 419 million years old (Ordovician and Silurian periods)
Bivalves have two shells, known as valves. Their shells are usually mirror images of each other.
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, mussels 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: beaches and cliffs around the coast of southern, eastern and northern England, South Wales and southern Scotland
Common in rocks aged: 201 million years old and younger (Jurassic Period onwards)
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 to find and identify. They are very common fossils in rocks over 66 million years old.
Brachiopods look very similar to bivalves, as they also have two shells. The best way to tell the difference is to compare the size and shape of the two shells. In brachiopods one shell is usually bigger than the other, and the larger shell has a small hole at the top.
Good places to find brachiopod fossils: southern, eastern and northern England, Wales and southern Scotland, particularly on the coast where rocks are exposed
Common in rocks aged: 541 to 66 million years old (Palaeozoic and Mesozoic eras)
Sponges are ancient animals that mostly live in the sea. Their bodies consist of simple groups of cells which can arrange themselves into large and complex shapes.
Some sponges produce a skeleton made of silica (the hard substance that sand is usually made of).
When sponges fossilise, the silica sometimes dissolves and then forms flint. This rock sometimes preserves fossils, including other sponges. So you can often 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.
Flint is usually dark grey or brown but it often occurs in lumps with a thin, white outer layer.
Good places to find fossil sponges: pebbly beaches in southern and eastern England, particularly ones close to chalk cliffs
Common in rocks aged: 145 to 66 million years old (Cretaceous Period)
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.
When the animal is alive, its skeleton is covered with skin and 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 round lumps 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-like pattern on it - you might get lucky.
Good places to find sea urchin fossils: pebbly beaches in southern and eastern England, particularly those near chalk cliffs
Common in rocks aged: 201 to 66 million years old (Jurassic and Cretaceous periods)
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.
Sharks have been around for a very long time - the oldest shark fossils discovered are more than 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
Common in rocks aged: 56 to 34 million years old (Eocene Epoch)
Bones of dinosaurs and other reptiles
Dinosaurs are probably the most famous prehistoric animals. At the same time as they were walking about on land, other enormous reptiles were living in the sea. But around 66 million years ago, dinosaurs and most marine reptiles died out.
Because of where dinosaurs lived, their bones are usually found in rocks that formed in swamps and river valleys. 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 marine reptiles such as ichthyosaurs and plesiosaurs are disc-shaped. But beware: pieces of flint can often look like bones.
Good places to find dinosaur bones: Isle of Wight. The best beaches to try are Yaverland and Compton Bay. Or you may find dinosaur footprints at North Bay, Scarborough or on the Isle of Skye.
Common in rocks aged: 201 to 125 million years old (Jurassic and Early Cretaceous periods)
Good places to find marine reptile fossils: Charmouth in Dorset and Whitby in Yorkshire
Common in rocks aged: 201 to 145 million years old (Jurassic Period)
Common UK fossils
The fossils above aren't the only ones you can find in the UK. Other common fossils include creatures called belemnites, corals and gastropods, as well as fossil plants.
The Museum's Fossil Explorer app covers nearly 90 fossil groups and will help you identify fossils based on where you find them. It's free to download.