Ohio: Isotelus (state fossil)
Ohio: Isotelus (state fossil)
Ohio's state fossil, the trilobite Isotelus, is among the largest trilobites known. It lived in the shallow seas that covered Ohio during the Ordovician Period, some 500 to 420 million years ago. Although over 20,000 species of trilobites are known, Isotelus was a predatory giant among its fellows, crawling along the sea floor in search of smaller creatures to feed on. It has even been referred to as the "T. rex of the Ordovician seas"!
Trilobites (a name meaning "three-lobed") were a very successful group of arthropods during the Paleozoic Era. As arthropods -- relatives of modern insects and crabs -- they had a segmented body, jointed appendages, and a tough exoskeleton. Usually only the exoskeleton is found as a fossil, but occasional specimens of some trilobites have been found which show that underneath the shell was the body of an animal somewhat similar to a pill bug, with a pair of legs on every segment, and even antennae. Why the group died out remains a mystery, but the mass extinction at the end of the Paleozoic Era rang the death knell for over 90% of the world's species, trilobites included.
A partial specimen of a large specimen of Isotelus was discovered during a geological survey of Ohio in 1837-38. A complete, 14.5 inch specimen was uncovered in 1919 during construction of the Huffman Dam near Dayton. While the largest complete Isotelus known measures 16 inches, partial remains indicate that the largest individuals may have grown to as much as 28 inches.
Two elementary-school classes in Dayton proposed that the Huffman Dam trilobite be made the official state fossil. While declining to designate only that specific specimen, the legislature instead passed a bill naming the genus Isotelus, and it was signed by the governor on June 20, 1985.
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