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Trilobite

Explorer · ages 7 and underAdapted from Wikipedia
A collage of six different trilobite fossils, ancient sea creatures that lived hundreds of millions of years ago, showing the variety of their shapes.

What Are Trilobites?

Trilobites are marine arthropods. That means they were sea animals with jointed bodies. They are related to today's insects, spiders, and crabs. Their name means "three-lobed," which is a fun clue to how they looked.

Their Bodies

Trilobites had a hard outer shell called an exoskeleton. Their shell was made of calcite, a mineral. Most trilobites were about 3 to 10 centimetres long, but the biggest one was more than 70 centimetres long.

Trilobites had complex compound eyes, so they could see well. Many fossils show them curled up in a ball, which may have helped keep them safe.

Long Ago

Trilobites first appear in the fossil record about 521 million years ago. They lived in oceans for almost 270 million years. Over 22,000 kinds have been described by scientists.

Trilobites were most common during the Ordovician and Silurian times. Later, they became fewer and fewer. The last trilobites were gone by the end of the Permian time, about 251.9 million years ago.

Fossils Today

Trilobite fossils are easy to find, and they are found all over the world. People have found them in places like Utah, Ohio, and Wales. In Hamburg, New York, visitors can even collect trilobites themselves.

Trilobites help scientists learn about very old rocks. Their fossils have been studied by people like Johann Walch, who made the first full study of the group. Long ago, the Ute Native Americans wore trilobite fossils as lucky charms.

Quiz time!

3 questions about Trilobite

Question 1 of 3

What kind of animals were trilobites?

Pictures

A scientific drawing of Thulaspis, an ancient sea creature from long ago, showing its legs and body parts from the top and bottom.
A scientific reconstruction showing what the ancient sea creature Squamacula clypeata may have looked like from above. It lived over 500 million years ago, during the Cambrian period.
A scientific reconstruction showing what the ancient sea creature Zhiwenia coronata may have looked like from above, based on fossils from the Cambrian period.
A scientific drawing showing how the ancient sea creature Acanthomeridion serratum may have looked from its top side and its underside, based on fossil evidence.
An artist's reconstruction of Sidneyia inexpectans, an ancient sea creature that lived over 500 million years ago during the Cambrian period.
A scientific reconstruction of Cheloniellon calmani, an ancient arthropod that lived during the Devonian period, around 400 million years ago.
A scientific drawing showing how the extinct sea creature Emeraldella brutoni may have looked from the side, from above, and from below, based on fossil evidence from the Cambrian period.
A scientific drawing of Aglaspis spinifer, an ancient arthropod that lived during the Cambrian period, over 500 million years ago. The tips of its antennae are based on educated guesses, since fossils don't preserve them clearly.
An artist's reconstruction of Retifacies abnormalis, a large arthropod that lived in the sea during the Cambrian period, over 500 million years ago.
An artist's reconstruction of Pygmaclypeatus daziensis, a small trilobite that lived in the sea long ago.
A scientific reconstruction of Naraoia magna, a small creature that lived in the seas over 500 million years ago, shown with its legs.
An artist's reconstruction of Kuamaia lata, an extinct animal, showing how it may have looked when it was alive.
A reconstruction of Kodymirus vagans, an ancient, mysterious arthropod that lived in what is now the Czech Republic. Scientists think it may be related to the aglaspidids, another group of early arthropods.
A diagram showing how the body features of Xandarellida, an extinct group of tiny Cambrian sea creatures, may have changed over time, based on family-tree analyses.
Redlichiida, such as this Paradoxides, may represent the ancestral trilobites.
Fossil Prochuangia from the Cambrian period of Darnjal Formation, Tabas, Iran
Cruziana, fossil trilobite-burrowing trace
A trilobite fragment (T) in a thin-section of an Ordovician limestone; E=echinoderm; scale bar is 2 mm.
Life reconstruction of Trimerus delphinocephalus, showing the dense setae covering the arthropod's body
The trilobite body is divided into three major sections (tagmata): 1 – cephalon; 2 – thorax; 3 – pygidium. Trilobites are so named for the three longitudinal lobes: 4 – right pleural lobe; 5 – axial lobe; 6 – left pleural lobe; the antennae and legs are not shown in these diagrams.
Diagram showing the three kinds of facial sutures in trilobites
Life reconstruction of Triarthrus eatoni based on preserved soft body parts
Olenoides serratus male diagrammatic reconstruction
An exceptionally well preserved Olenoides serratus from the Burgess Shale. The antennae and legs are preserved as reflective carbon film.
Unknown Phacops sp. eye
The schizochroal eye of Erbenochile erbenii; the eye shade is unequivocal evidence that some trilobites were diurnal.
Five stages in the development of Sao hirsuta
Drawing of Ogygiocarella debuchii by Rev. Edward Lhwyd, made in 1698

Keep exploring

Arthropod
Animal
Exoskeleton
Calcite
Compound eye
Ordovician

This article is a child-friendly adaptation of the Wikipedia article on Trilobite, available under CC BY-SA 4.0.

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