Trilobites (meaning three sections) are an extinct sea-bed animal that has been very important in geological studies.

Trilobites could walk on the sea-bed or swim in shallow water. They were scavengers that regularly moulted their skeleton.

The first trilobites were found in Lower Cambrian rocks 500 million years ago, and so they are among the earliest of fossils. The Cambrian Period has been called the Age of Trilobites. They show considerable variation in shape and size. Some grew to be over half a metre long.

Trilobites became most numerous and most varied in the next geological age, and then began to decline, so, although they were still important in the 400 million years ago, they were rare by the Carboniferous Period, 300 million years ago, and became extinct in Permian times, 250 million years ago.

Recognising trilobites
The oval shapes of trilobites are quite distinctive. They also have many lines across them. There are no lines on the head, and the head is more bulbous than the tail.

Recognising parts of trilobites and those that have been squashed is more difficult. It is quite common to find tails, but the lines running across the tail section should be easy to spot.

It is also common for some trilobites to be curled up, so do not expect to always find them as flat shapes.