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Fossil Friday- Isotelus rex, King of the trilobites
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Isotelus is the state fossil of Ohio, and is one of the largest trilobites yet found (a new contender for the title was found in Portugal). It is found in Ordovician age rocks throughout the Great Lakes region of the United States and Canada, as well as in Europe. The largest specimen, described as Isotelus rex, measured 28 inches (72 cm) in length, and was found in Manitoba, Canada.
Trilobites are an extinct group of arthropods related to insects, crustaceans, and horseshoe crabs. Their fossils are fairly common in early to mid Paleozoic age rocks. Their numbers dwindled later on in the Paleozoic, before going extinct at the Permian-Triassic extinction.
The name trilobite is in reference to the three (tri-) lobes which run down the length of the animal's shell. The center (axial) lobe raised up above the side (plueral) lobes. In Isotelus however, these are not well developed, in many cases the axial lobe is so indistinct it just seems to blend with the rest of the animal. The head (cephalon) and tail (pygidium) areas of Isotelus generally resemble large, smooth semicircles while the thorax is relatively short compared to most trilobites, consisting typically of just eight segments.
Pennsylvania and Wisconsin also have trilobites as their state fossil.
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