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Trilobites are hard-shelled, segmented creatures that existed over 300 million years ago in Earth's ancient seas. Trilobite fossils are found worldwide, with thousands of known species. The smallest known trilobite species is under a millimetre long, while the largest include species from 30 to over 70 cm in length. Whatever their size, all trilobite fossils have a similar body plan, being made of three main body parts: a cephalon (head), a segmented thorax, and a pygidium (tail). Similar to lobsters and crabs, trilobites would have physically grown during a molting stage, where the exoskeleton would split between the head and thorax. Trilobites went extinct before the dinosaurs even came in to existence and are one of the key signature creatures of the Paleozoic Era.
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Oct 17, 2009, 3:42:12 PM
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