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Trilobites - The Dinosaurs of the Arthropod Family

Everything You Ever Needed to Know About Trilobites

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trilobite

A fossil of a typical trilobite, Arctinurus boltoni (courtesy of Trilobites.com)

Tens of millions of years before the first dinosaurs walked the earth, another family of strange, distinctive, weirdly prehistoric-looking creatures, the trilobites, populated the ancient oceans--and left an equally abundant fossil record.

The Trilobite Family

Trilobites were early examples of arthropods, a vast phylum that today includes such diverse creatures as lobsters, cockroaches and millipedes. These creatures had three main body parts: the cephalon (head), thorax (body), and pygidium (tail). Oddly, the name “trilobite,” which means “three-lobed,” doesn’t refer to this animal’s top-to-bottom body plan, but to certain features of its axial (left-to-right) appearance.

The trilobites comprised ten separate orders and thousands of species, ranging in size from less than a millimeter to well over two feet. These beetle-like creatures appear to have fed mostly on plankton, and they inhabited a typical array of undersea niches: some scavenging, some sedentary, and some crawling along the ocean bottom.

Trilobites and Paleontology

While trilobites are fascinating for their diversity (not to mention their alien appearance), paleontologists are fond of them for another reason: their hard shells fossilized very easily, providing a convenient “road map” to the Paleozoic Era (which stretched from the Cambrian, about 500 million years ago, to the Permian, about 250 million years ago).

Unfortunately, the last of the trilobites were wiped out in the Permian Extinction, a global catastrophe that killed off more than half of the earth’s species. What exactly brought about their downfall isn’t clear, though the evolution of larger, predatory creatures (like sharks) certainly didn’t help.

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