Other fossil arthropods

Many other arthropods, besides trilobites, have been seen in the fossil record and most of them are now extinct.

Sea scorpions (eurypterids), lived mainly in coastal lagoons and freshwater, though some early forms lived in the sea. Related to spiders and scorpions, they were fierce predators that could grow up to two metres in length. They died out at the same time as the trilobites.

Horseshoe crabs are also related to spiders and scorpions. They have a large circular body, twelve legs and a long tail spine. They first appeared about 400 million years ago and became the 'modern' shape about 250 million years ago. They can still can be found living in coastal waters in Asia and on the eastern shores of North America, and are sometimes referred to as living fossils.