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Trilobite Fossils

Trilobites are an ancient variety of arthropods and were one of the first animals to have eyes. Some are nearly 550 million years old! They're also one of the most popular invertebrate fossils with thousands of species to collect. You can choose small flat specimens or rolled into a tight protective ball and occasionally you'll even find one in a half-curled position as if it were crawling over a rock. You'll find a variety of trilobite fossils for sale from around the world including Morocco and the well known Wheeler Shale Formation. 

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trilobite parts

trilobite drawing

When did Trilobites Live?

The first trilobites show up in the fossil record early in the Cambrian Period about 540 million years ago. They were on the vanguard of the "Cambrian Explosion", a time when many animals had hard body parts that could fossilize. They rapidly diversified through the Ordovician Period and were abundant. However something happened during the Ordovician Period that was not good for the trilobites. It may have been a change in the earth's climate like an ice age. Whatever it was many species of trilobites became extinct later in the Ordovician. Their numbers continued to decline during the Paleozoic Era. They finally went extinct during the Great Dying of the Permian Extinction.

Trilobite Body Plan

Trilobites get their name from the 3 lobes of their bodies from side to side. There were also 3 sections to their bodies from front to back, the head or cephalon, the body or thorax, and the tail called the pygidium. The thorax had flexible sections that allowed trilobites to curl up into a ball to protect their bellies like a sow bug.

trilobite lobes

Trilobite Size

Some trilobites were very small. Perisphinctus for example only grew to about 5 mm or 1/4 inch. The largest species is called Isotelus rex. This huge arthropod could be 720 mm long, more than 2 feet . Most trilobites were 1 -2 inches long. Because they had exoskeletons they had to molt as they grew. In order to molt the outer shell protecting their bodies split at the front of the cephalon and the trilobite ctrawled out. It took some time for the new "skin to harden. A typical trilobite might molt 20 times or more during their lifetime!

The Trilobite family

There have been more than 25 thousand species of trilobites described devided into the following 12 orders:


Trilobites were so diverse that there were species filling every niche in the ecosystem of the Paleozoic Era. They were predators, scavengers, and filter feeders. They crawled, burrowed, and swam freely.
They have been found all over the world.

Hunting Trilobites in Morocco

Hunting trilobites in Morocco

Learn More about trilobites

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INTERESTED IN MORE INFORMATION? IF SO, YOU MAY WANT TO CHECK OUT OUR OTHER SITES: - An educational site about fossils and geologic time - An educational site about rocks, minerals, and geology.

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