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Trilobites represent a group of sea-living animals that have been extinct for over 250 million years. They are known mainly from their exoskeletons, or shells, that provided a hard protective layer to which soft body tissues and legs were attached during life. The body plan of the trilobite exoskeleton is relatively complex. The name ‘trilobite’ comes from a division of the exoskeleton width-ways into three lobes, 'tri-lobe-ite'. The division is seen as a raised axial region running down the whole length of the trilobite much like a spine, and two flat regions each side called the pleural fields. Another division of three occurs lengthways with a definite head end (the cephalon), middle region (the thorax), and tail (the pygidium).

Everything we know about trilobites comes from fossils, and only relatively recently have they been found with details of segmented legs and antennae. This tells palaeontologists that trilobites are closely related to modern insects, crustaceans and arachnids (spiders and scorpions) grouped together as the arthropods.

There are nine groups of trilobites: the Agnostida, Redlichida, Ptychoparida, Corynexochida, Lichida, Asaphida, Harpetida, Phacopida, Proetida. This website concentrates on the redlichids.

Some trilobites were big!

Paradoxidid trilobites could grow to a large size.
(Suborder Redlichina; Superfamily Redlicoidea)

Author: Sue Beardmore
Last updated: 18/11/06

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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2006-7