The trilobite is not only the state
fossil of
Wisconsin (
Calymene celebra), it is also the state fossil of
Ohio (
Isotelus) and
Pennsylvania (
Phacops rana).
These marine
arthropods first appeared 570 million years ago and survived for more than 300 million years (longer than
dinosaurs and
humans). Trilobites were one of the first living creatures to secrete hard shells which allowed them to be fossilized. They are found in
Paleozoic sedimentary rocks around the world.
The word trilobite means "three-lobed" in
Greek. This described the body of the trilobite which was divided into three sections: the head, the segmented
thorax, and the tail. These three sections each had a pair of legs and
gill-like appendages which were probably used for swimming or breathing.