Fossils within fossils
Sometimes, a fossil animal is found with another fossil animal inside it. The larger animal may have been pregnant with young at the time it died, in which case the animal inside is an unborn baby animal. In other cases, the animal inside was eaten by the larger animal just before the larger animal died, and become fossilised with it.

Do dead animal always turn into fossils?
When animal die, the bone are usually chewed by other, scavenging animals, scattered by the rain and wind, or bleached broken down to dust by the Sun. For this reason, the bones of most animals that have ever lived, nomore than one in a million has survived as a fossil. Fossil form only when a dead animal is buried quickly by sediments, before there is a chance for the bones to be destroyed. When this happen, the bones are locked up in the sediment as it slowly turns to rock. The bones themselves also turn to rock in the process, but they keep their shape. Millions of years later, erosion strips away the layer of rock and exposes the fossil.

Four fossils form
1. Cover up :
The dinosaur lies on the mud in shallow water, which keeps scavenging animal away.

2. Rot set in :
Sediment starts to settle on the dinosaurs body. Meanwhile, bacteria attack the body's soft
parts, making them rot away.

3. Dead and buried :
After hundreds of years, the bones are safely buried beneath the surface. Water
seeps into the bones, leaving behind minerals that help to turn the bones into fossils.

4. Finished fossil :
As a sediment piles up, pressure grows. After thousands of years, this turns the sediment
and fossils into rock.

What are the best places to find fossils?
Fossils are found in rocks such as chalk, limestone, sandstone and shale. These were formed long ago by sediments building up on the seabed or at the bottoms of lakes. They are called 'sedimentary rocks' Rocks form by volcanic action, such as granite and basalt, do not contain fossils. You can find fossils where sedimentary rocks are being cut away by erosion, such as in sea cliffs or river gorges.

FOSSIL TRAILS

No one has ever seen a tyrannosaurus, or any other dinosaur, but we know a lot about them. Almost all our knowledge about prehistoric animal comes from fossils, which are rock-like 'model' of the bones of animals. The bone themselves were buried in layers of mud or sand, millions of years ago, and then slowly turned to rock themselves by a natural chemical process. Very rarely, softer parts of the body such as skin, feathers and fur also become fossilised, giving many useful clues about life in the past.

How fossils form?
If a dinosaur dies beside a lake and falls into the shallow water, it has a very good chance of slowly turning into a fossil. The dinosaur's body is slowly covered by muddy sediment. Its skin and flesh start to rot away, leaving just the bare bones are completely covered up, they do not break down any more. Instead, they are slowly fossilised, or turned into rock.

Why do some animals become extinct?
Some creatures die out, or become extinct, while others flourish. This is part of the process of evolution. Successful species move into new areas, or start eating new food, or adapt to a change in climate, and so evolve into new forms. The extinctions make space for new species to emerge. Human activities such as forest clearance, building and road-making, which are not part of a natural process, are now also causing extinctions, too quickly for evolution to fill the gaps. We are now losing thousands of species every day, and they are not being replaced.

Why does a pangolin look like an armadillo?
Sometimes animals that live in the same way and eat much the same food evolve to look like each other, even though they are not closely related. The armadillo's main diet is ants and termites, which it digs out of the ground with powerful claws. It has a long snout for nosing around in the ground after insects, and thick plates of bone protecting its skin from the ants painful stings. This bony armour also gives it protection from predators out on the open plains where the ant nests are found. Armadillos live only in the Americas, but in Africa there are animals called pangolins that look remarkable similar. They, too, live out on the plains and feed mainly on termites and ants. The pangolins and armadillos are not related, but because they live the same kind of life, they have evolved along similar lines. This is called convergent evolution.