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Trilobites were interesting creatures known as arthropods that came in a wide variety of sizes and species. They existed and became extinct before the dinosaurs were around, more than 250 million years ago during the Paleozoic Era. Trilobites appeared about 520 million years ago in the Cambrian and persisted until the Permian (about 250 million years ago), so survived for about 270 millions years. Quite a feat! They lived in all the seas of the world and have been found as fossils on all continents in more than 20,000 species.

Trilobites had a size range of from 1 millimeter to around 70 centimeters, averaging around 2.5 centimeters (around an inch). The trilobite's body can be "divided up" in two ways. The first is from front to back, into a cephalon ("head"), thorax (sort of a "torso" that was divided into segments) and a pygidium ("tail"). Although this way of dividing the body amounts to 3 sections, that is not what the name trilobite ("three lobed") refers to. The name actually refers to the three lobes that run the length of the body from head to tail. They are called the central axial lobe (think "axis" or middle) and left and right pleural (side, or rib) lobes.

One interesting thing about trilobites is that these fossil animals can be held in your hand to be examined. You could not do that with a dinosaur or an elephant!

Another interesting fact is that most, but not all, trilobites had compound (multi-lensed) eyes. Living arthropods (such as insects) often have compound eyes that are good for detecting motion and predators.

The fossil record shows that trilobites were only marine (sea) animals, not fresh-water dwelling, and lived in a diversity of ocean/sea habitats, from shallow water to reef areas and deep ocean areas, and from tropical to polar biomes. Adaptable describes this large family of arthropods. It is thought that the majority of trilobites were predatory scavengers.

An excellent site giving a lot information about trilobites and research can be found at this link: Trilobite.

On a more "personal" (or at least local, for me) level is an interesting fact. The state fossil of Pennyslvania is Phacops Rana. The state legislature came to this decision with legislation in 1988. If you are a Pennsylvania resident wanting to see a trilobite "in the wild" or would like to collect one for yourself, the state does have a guide to where you can go to find them, in Swatara State Park in Lebanon and Schuylkill Counties.

More about this author: Rick Bavera

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