Wilderness Underfoot: World's finest fossil worms

StoryImage( ‘/Images/Story//Auto-img-11581749373282.jpg’, ”, ‘Our most common fossil worm — Didontogaster cordylina (shown in its living form, above, and as a fossil, right) can be found in 300 million-year-old fossils near the city of Braidwood, Ill. This predator's first Latin name means "two teeth in the stomach"–referring to a pair of tiny "teeth" (shown enlarged on the fossil illustration) that helped the worm grind up its prey. The dark line down the center of the fossil worm is its digestive tract. Didontogaster reached about 3.5 inches in length. Living relatives belonging to this worm's family, Nephtyidae, are widespread today in silty nearshore and offshore marine waters. They're often called shimmy worms or painted worms, and they can be found burrowing or crawling on the mud when the tide goes out.’);
StoryImage( ‘/Images/Story//Auto-img-11581750683282.jpg’, ”, ‘A much less common fossil worm — Rutellifrons wolfforum was another predator. Unlike Didontogaster, however, this worm didn't appear to have "teeth" or jaws. Living members of Rutellifrons' family, Hesionidae, are found in marine environments all over the world.’);

We have more finely preserved prehistoric worms than any other place on earth.

Although they might not attract the attention of most fossil collectors and amateur paleontologists, for what it’s worth, Illinois has bragging rights when it comes to fossil worms. Our worms are so good that even their tiny hairs, “teeth” and digestive tracts are preserved.

These are annelids—a large group of worms with segmented bodies. Modern-day earthworms are also annelids, but the worms found in Illinois fossils actually belong to a different class of annelid known as “Polychaeta,” which have bristly hairs. The Polychaete’s history stretches back at least a half-billion years. More than 8,000 species are still living today, primarily in marine waters.

Our fossil worms are found in

300 million-year-old coal deposits in the north-central part of the state. These creatures lived in nearshore marine waters on the edge of a tropical rainforest that covered our region during the Carboniferous Period. Today, the fossil locality is called the Mazon Creek region, named after the small river where these fossils were first found.

In this locality alone, 14 worm species have been described, belonging to 12 families. Worms are so abundant among the Mazon Creek fossils that a hoard of undescribed species may yet be found stashed away among the other, more highly appreciated, finds that are now in the hands of collectors.

Most of these worms were predatory, consuming smaller invertebrates on the muddy sea floor. Some were capable of freely roaming about in search of food, while others hid in burrows and sprang out to catch their prey, and still others were simply attached to rocks and debris.

From the Sept. 13-19, 2006, issue

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