Trilobites

The Cambrian, Ordovician and Silurian periods (from 590 to 410 million years) ago make up the first half of the Palaeozoic Era. They witnessed a great burst of evolutionary development, with new and unusual creatures stocking the Earth's oceans.

For much of this time, southern Alberta was covered by a shallow sea, as were many parts of present-day continents. A host of shelled invertebrates swarmed in the seas. Echinoderms, with skeletons of hard, connected plates, became abundant. Many animals that live in colonies, including the first true corals, appeared. Trilobites, relative of the modern horseshoe crab, were diverse and abundant.

Trilobites were marine invertebrates with three-lobed shells. They appeared at the beginning of the Palaeozoic Era.

Among the first animals to develop hard skeletons over their bodies, trilobites left large numbers of fossils around the world. Many have been found in clusters, probably the remains of shells shed prior to mating. Their tracks also survive as fossils.

They protected themselves in many different ways. Some burrowed into the mud. Others evolved spines, or the ability to roll up in tight ball. Several species grew too large for predators to handle.

Even so, they all became extinct. Their relatives are common in our world however. Eighty per cent of all living animals share a common ancestor with trilobites.

This document was prepared by Wayne Hortensius, Calgary, Alberta, Canada for the Royal Tyrrell Museum Cooperating Society. All information © 1995 Royal Tyrrell Museum. All Rights Reserved.
Updated: April 8, 1995

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