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There are well over ten thousand species of trilobites known from around the world. Trilobites had their highest diversity during the Cambrian Period, slowly diminishing through the Paleozoic until their extinction in the Middle Permian, a longevity of some 280 million years. Trilobites belong to the Phylum Arthropoda, and are characterized by a chitinous skeleton divided lengthwise into three prominent lobes, the medially located axial lobe, and two lateral pleural lobes. They have a head shield (cephalon or cranidium), several thoracic segments, and a tail (pygidium). A single trilobite could produce many individual fossils. Everytime a trilobite would molt (shed its exoskeleton in order for the animal to grow larger), it would leave behind an old shell which may have fossilized, then the trilobite would grow a new one. The process continued periodically throughout its life. Usually only the hard exoskeleton of trilobites is preserved with extremely rare exceptions. Incredible soft-bodied preservation of trilobites and other animals can be seen in many specimens from the world famous Burgess Shale in British Columbia, the Beecher Trilobite Beds of New York, and the Hunsrck Slates of Bundenbach in Germany.

Trilobite classification is a confusing matter. No classification can be based on a single feature of the exoskeleton, although the cephalic sutures between the cephalon and the free cheeks are strongly relied upon in higher groupings in trilobite classifications, along with other cephalic axial characters. There are six orders of trilobites and several families placed into uncertain order status. The six orders include: (1) Agnostida; (2) Redlichiida; (3) Corynexochida; (4) Ptychopariida; (5) Lichida; and (6) Odontopleurida.

Trilobite background information provided by Andrew R. Milner;
Hanman's Fossils and Minerals
info@hanmansfossils.com    www.hanmansfossils.com

Illustration from The Fossil Book; Patricia Rich, Thomas Rich, Mildred Fenton, and Carol Fenton; Dover Press, 1996.

Ilaenus tauricornis

Kundsky Hrzn., Wolchov River, Near St. Petersburg, Russia
Ordovician, about 455 million years old.
Matrix is about 60 mm (2.5 inches) across.

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