For nearly 300 million years, the Tully monster lay buried just south of Chicago-until one summer day about 40 years ago, when a probing fossil hunter dug him up.
No one had ever seen anything like this foot-long creature with a trunk, a worm-like body, and fins. It was named after its discoverer, Francis Tully, and became the state fossil.
Over the years, many Tully monsters have been found in the area, but nowhere else in the world.
And anyone inspired by the “Jurassic Park” phenomenon who is seriously interested in getting a glimpse of life 300 million years ago can follow Tully’s footsteps through the world-famous fossil bed in the Mazonia-Braidwood Conserve, about 60 miles southwest of Chicago via Interstate Highway 55. (There is construction on the highway, but route changes are marked.)
“The Mazonia-Braidwood area is one of only three places in the world where you can find fossils showing the soft parts as well as the skeletal structure of plants and animals-it’s like finding a whole dinosaur, instead of just its skeleton,” says Northeastern Illinois University earth science professor Chris Ledvina, fossil-hunting co-ordinator and curator of the Mazon Creek Project. This is where dinosaur expert Paul Sereno first got interested in fossils.
“I went fossil hunting there with the neighborhood kids,” says Sereno, a University of Chicago professor who recently discovered the fossil of the world’s most primitive dinosaur-the 225-million-year-old eoraptor-in the foothills of the Andes Mountains. About 90 million years before the first giant dinosaurs, the Mazonia-Braidwood Conserve was part of a lush, tropical swamp teeming with primitive plants and animals.
Nearby lay the northeastern coast of the primordial Sea of Illinois, part of a shallow, warm saltwater estuary that covered much of the Midwest. A river and delta flowed through the area, sometimes flooding it and burying both saltwater and freshwater plants and animals under layers of mud. Over time, millions of organisms were buried alive and beautifully preserved in petrified peat (coal).
“The plants and animals were buried so quickly, some didn’t even start to decay, and that’s why their fossils are so distinct they show both soft and hard parts of the organism,” says Field Museum’s Peter Laraba, who conducts the museum’s fossil-hunting field trips for families as well as avid collectors. Some fossils even capture what was happening as the creature was being buried. Split open a rock, and you might see one 300-million-year-old fish eating another.
“Many fossils are so well preserved and from such a wide range of environments that they give the most complete picture we can get of life 300 million years ago,” says Laraba.
“The area marks a major occurrence of soft-bodied fossil remains on this planet,” says Roger Bohn, vice president of the Chicago Area Paleontologist Society. “How can you have something like this practically in your back yard and not investigate?”
For more than a century, the area has attracted paleontologists and avid fossil collectors from around the world. Fossils found there are displayed in museums worldwide. So far, 500 different plant and animal species have been found in the area. Ancient squid, shrimp, sea cucumbers, jelly fish ferns, spiders and dragonflies have been uncovered in the smooth, rust-colored rocks called “concretions.” Some fossils had never before been seen and some have never been found anywhere else. Many more lie hidden among the shale piles.
There is always the possibility that someone will find a new “monster” fossil. Fossil collectors don’t need the usual hard hat, hammer, and chisel used at other fossil-collecting sites.
“It’s one of the easiest places to collect fossils,” says Laraba, “because many concretions have already been dug up and exposed through weathering.”
The Conserve is part of a network of 70 square miles of abandoned coal mines that left mounds of fossils uncovered. When the mines were closed in the mid-1970s, after more than 100 years in operation, some were inundated when the cooling lake was formed for Commonwealth Edison’s Braidwood Nuclear Power Station. Some of the fossil-hunting ground in the wider Braidwood area outside the Conserve has restricted access, but Commonwealth Edison is helping fossil hunters at the cooling lake, which is within the Conserve.
“We realize this is an important fossil site, and we want to keep it open to serious fossil collectors,” says Gary Wald, nuclear communications administrator at Commonwealth Edison. Fossil treasures lie in heaps on islands in the 2,600-acre cooling lake. Fossils can also be found along the shore and throughout the thousands of acres of the Conserve.
From April through September, fossil-hunters can hike and paddle through this lake area, which, as part of the Mazonia-Braidwood Conserve, is maintained by the Illinois Department of Conservation.
“The islands in the cooling lake offer some of the best fossil hunting ground in the world and they are off-limits to everyone except serious fossil hunters,” says Gale (“Doc”) Guynn, Department of Conservation site assistant superintendent.
Fossil hunters in this area must have permits (issued free of charge by Northeastern Illinois University).
The fossils found in this region are known as Mazon Creek specimens, named after nearby Mazon Creek, where fossil hunting began more than a century ago.
The Mazon Creek fossils were formed during the Coal Age (also known as the Pennsylvanian Age) about 280 million years ago when coastal swamps developed and peat deposits formed. Later, these turned to coal.
Mazon Creek fossils are found in smooth round or oval rocks. They range from an inch to a foot or more in diameter. They are usually gray, brown or rust colored.
“Even if you’re not an experienced fossil hunter you’ve got a good chance of finding a fossil,” says Laraba. “But it helps to know what you’re looking for,” says Bohn. “Otherwise you won’t really know what you’ve found.” Bohn recommends studying up on Mazon Creek fossils before driving out.
