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Trilobites, the three-lobed sea animals

Trilobites: crystal eyes, a roll-up suit of armour, and 250 million years in the sea.

What trilobites were, how their bodies and calcite eyes worked, what they ate, how big they grew, why they died out, and how one of them became the Dudley Bug on a town’s coat of arms. Every fact is linked to its source, and there is a quiz at the end.

Meet the animal Take the quiz

A dark brown fossil trilobite lying on its side, its rounded head, ridged segmented body and small tail clearly visible
Calymene blumenbachii, the Dudley Bug, from the Much Wenlock Limestone at Wren’s Nest, Dudley.Picture: James St. John, CC BY 2.0, via Wikimedia Commons (cropped and resized)
20,000+species described NHM
250 million+years in the sea NHM
72 cmthe biggest, Isotelus rex NHM
1.5 mmthe smallest NHM

The short version

Trilobites were sea animals and arthropods, the group that includes insects, spiders and crustaceans. NHM

The word trilobite means ‘three lobes’. NHM

Trilobite eyes were made of calcite, a crystal: the NHM says no other animal is known to have had that before or since. NHM

The first are known from around 520 million years ago. NHM

They vanish from the fossil record just before the Great Dying at the end of the Permian, when 90% of animals were wiped out. NHM

Among extinct animals, trilobites are probably second only to dinosaurs in fame. UCMP Berkeley

Good sources disagree on some details, such as when trilobites first appeared and when they finally died out. Where they differ, we show each version side by side.

A brown fossil trilobite seen from above in a rock, with a broad rounded head, two raised eyes and a segmented body
Calymene blumenbachii at the Natural History Museum, London.Picture: Captmondo, CC BY-SA 3.0, via Wikimedia Commons (cropped and resized)
The parts of a trilobite, based on Calymene.Drawing: our own, simplified and not to scale

Explore

The animalThree lobes, jointed legs, a roll-up body. Crystal eyesEyes made of calcite. Life and sizeHunters, grazers and a trident. Deep timeSix periods and a slow goodbye. The Dudley BugWren’s Nest and a coat of arms. Trilobites and peopleMerlin, a fish and an amulet. MythsAre trilobites still alive? No. GamesQuiz, myth or fact and the trilobite-o-meter.

Tile pictures are credited on their pages and on the credits page.

Try the games

A 12-question quiz, a myth-or-fact challenge, and a trilobite-o-meter that measures you in trilobites.

Play now

Trilobites is the third site in the fossils.im network. For the spiral shells of the Jurassic seas, visit ammonites.fossils.im; for the giant shark known from its teeth, visit megalodon.fossils.im.