Wilderness Underfoot: Creepy crawlies of prehistoric Illinois seas

StoryImage( ‘/Images/Story//Auto-img-118175225512684.jpg’, ”, ‘Trilobites on the sea floor – Calymene celebra searching for worms, about 420 million years ago (middle Silurian Period).‘);
StoryImage( ‘/Images/Story//Auto-img-118175229314224.jpg’, ”, ‘One of our region’s most stunning fossils – Ceraurus pleurexanthemus is rarely found in such perfect condition as this, but in some areas, broken pieces of this trilobite are quite abundant. It lived about 440 million years ago (middle Ordovician Period).‘);
StoryImage( ‘/Images/Story//Auto-img-118175232232673.jpg’, ”, ‘Curling up for defense – Bumastoides milleri fossils, flattened and enrolled. This trilobite lived about 440 million years ago (middle Ordovician Period).‘);

Trilobites—among the most diverse and interesting arthropods of all time—first appeared in shallow seas about half a billion years ago.

They’ve been extinct for 250 million years, but these marine arthropods continue to excite paleontologists and amateur scientists alike.

The name “trilobite” means three-lobed one, referring to three lobes along the length of its body. In ancient times, these arthropods crawled around the sea floor, feeding on detritus, micro-organisms, worms or other creatures, depending on the species. The trilobite line, now extinct, appears to have split off from another line of animals that led to modern chelicerates such as spiders, scorpions, ticks, mites and horseshoe crabs. During much of the Paleozoic Era, trilobites were among the most successful and diverse of all creatures, and their gradual decline and ultimate extinction is still a mystery.

Collectors around the world are delighted to find fossilized remains of these creatures, and many are devoted to hunting for nothing but trilobites. Ranging from the size of a grain of sand to 28 inches long, with a variety of shapes from simple to ornate, and with more than 15,000 known species, trilobites offer a vast challenge for collectors. Interestingly, in some locations even the fossilized walking paths and burrows of these creatures have been discovered.

Trilobite fossils can be found in sedimentary rocks of our area, such as limestone, dolomite and shale. Gastropods (snails) and pelecypods (clams) are more common, but if you search a pile of crushed rock, you may also find at least part of a trilobite.

from the June 13-19, 2007, issue

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