Squid-like gastropods, such as the one found by Bev Sandlin, were top predators of the ancient sea.
Bev Sandlin is time traveling on the side of a county road. She picks up a small stone and imagines a time when the landmass that is now Southeast Minnesota was 150 feet under water and on the equator. For better or worse, our continent has since inched northward. Sandlin envisions a world dominated by bizarre aquatic beings: squid with shells shaped like a unicorn's horn (known as cephalopods), insect-like trilobites, and tentacled plants.
That world was very real at one time, and Sandlin is a recent initiate to the modern day exploration of it: fossil hunting. The same shallow sea that over 400 million years ago deposited the bedrock beneath Southeast Minnesota also left behind an incredible amount of evidence of its inhabitants.
To start finding fossils, all would-be fossil hunters need to do is look. "At every single road cut you will almost invariably find fossils," Sandlin said. "You don't have to have an axe or a pick or anything. Just walk around a road cut and look for weird rocks."
Fossils are so ubiquitous in the driftless region that heavily fossilized rocks are commonly used for commercial purposes. Sandlin was turned on to fossil hunting a year ago when she realized that the rocks that made up the retaining wall near her house were loaded with ancient plants and animals.
Relics of a more recent past are waiting to be discovered, as well. The Houston Nature Center is home to a number of Ice Age fossils (their young age may technically make them subfossils) that have been found in the area. The display includes the tusk and teeth from a wooly mammoth and the skull of giant bison that were discovered in the Root River valley. There have been numerous other Ice Age finds in the area, Houston Nature Center Naturalist Karla Bloem explains. The bones of now-extinct beasts are preserved in the sediment along the river. "When a river has cut into its banks, this stuff just pops out of the sediment," she said.
Like most people, Bloem was shocked to learn that Ice Age fossils were being found in her hometown. "I just kind of fell over dead," she laughed. "It's really cool and most people have absolutely no idea that this stuff is here."
Bloem related that the giant bison skull that is now on display at the nature center sat for years on the wall of a local farmer's granary. The farmer assumed the massive skull and horns were the product of modern buffalo. A nature center board member heard about the "buffalo" skull shortly after learning about mammoth teeth that had been found in the area. A light bulb went off in his head: maybe the skull was older than anyone thought. "Here this skull had just been pushed aside in the granary; 'Oh, yeah, that's cool, a big bison skull,'" Bloem laughed. It turned out that the board member's hunch was correct; the skull was from the now-extinct giant bison that roamed Minnesota during the last ice age. Modern buffalo have quite large heads, but this skull dwarfs them, Bloem explained.
The nature center acquired the skull and worked to preserve it.
"I always encourage people, after we have a flooding event, to go have a look-see. You never know what you might find," Bloem said.
Some Ordovician Era fossils — from the time of the ancient sea — are so common that collectors may gather hundreds. While picking through highly fossilized rock, one might find the fossils of dozens of ancient sea shells within a few minutes. With so many fossils at every turn, it is easy for area residents to be unimpressed. But fossil hunters are enthralled. There is a touch of tragedy in Sandlin's voice when she describes how fossil-bearing rocks are routinely ground up for gravel. For fossil hunters, even the most ubiquitous fossils are incredible marks from a forgotten world. Part of the magic of the experience, they say, is that every fossil is a chance to look into the alien world that was Minnesota so many millions of years ago.
"Imagine a sea without fish!" Sandlin writes on her blog, bluffcountryfossils.com, after a fossil hunt outside of Winona. "Cephalopods are the apex predator! Trilobites crawling around the bottom of the sea floor. No land plants or animals!"
The walls of Niagara Cave in Harmony offer a unique opportunity for imagining the creatures of that world. The walls of the cave are embedded with Ordovician fossils still in the rock layer that formed after they died.
"What's interesting is to try to figure out, when you find a layer that's really fossiliferous [full of fossils], is: why is this more fossiliferous than six inches above it or eight inches below it?" explained Mark Bishop, owner of Niagara Cave. "What was going on at that time? Was there a mass extinction? Did the currents carry all these creatures here? Was it volcanic event that killed them off? Did the water get too hot or too cold?"
The other reason fossil hunters are enthralled is the chance of finding a rare, prize fossil. What could be underneath the next stone? While fossilized sea shells may be a dime a dozen, other Ordovician relics keep folks searching for years.
"The trilobite is the most sought-after fossil in this area," said Bishop. Finding a complete trilobite is a crowning achievement for collectors. One Southeast Minnesota fossil-hunting blogger dedicates his site to photos of preserved bits of the horseshoe crab-like animals that he has discovered over the years. However, "A complete trilobite still eludes me," he pines.
Sandlin has other aims. "Those darn trilobites look like sea cockroaches to me," she said. Her prizes are gastropods, spiral-shelled squids that were one of the top predators of their time.
For Warren Netherton, manager of Mystery Cave State Park, cephalopods, which he describes as an "octopus with a dunce cap on," are the most exciting find. Perhaps one of the most impressive Ordovician finds in the area is the five-foot-long cephalopod fossil Bishop found near Harmony. "Something like that is a once in a lifetime thing," he said.
Bishop also hunts morel mushrooms and occasionally pans for gold. He is an admitted "rock hound," and it would seem that the thrill of striking gold, literally or figuratively, must have a strong appeal to him. Trilobites "don't taste as good as morels but they're still pretty exciting," he joked.
Perhaps the excitement can get out of hand, Sandlin suggested. "Just like there are gambling addicts, there are fossil addicts. When you reach out in the middle of the night and you are petting your cat, but you think that you're petting a trilobite, you've got a problem," she laughed. "But every rock that you turn over could be that gem that you've been after. Every stone could be that one."
"The thrill of discovery and being able to keep what you find is just a wonderful feeling of satisfaction for many people," Netheron said.
Fossil hunting tips
Would be fossil-hunters should look for limestone and dolomite road cuts or rock bars, Sandlin recommends. Sandstone does not tend to contain fossils. "When you're adjacent to the road, you're on public property and it is just a great place to look for fossils," Netherton said. Sandlin recommends former University of Minnesota paleontologist and current Winonan Robert Sloan's "Minnesota Fossils and Fossiliferous Rocks" as the best resource on local fossils. However, the internet is replete with resources as well.
For those interested in Ice Age subfossils, Bloem says that walking the banks of the Root River is the best way to search. Deposits of blue-colored clay are especially likely spots, she reports.
For those who would prefer to allow others to do the hunting, there are a number of fossil displays to admire. The Historic Bluff Country Visitor Center in Rushford, in conjunction with Sandlin's bluffcountryfossils.com, is pitching the area's paleontological attractions as a "Fossil Trail." The trail includes stops at fossil displays at the Houston Nature Center, Harmony Visitor Center (where Bishop's five-foot cephalopod is on display), Niagara Cave, and Mystery Cave State Park. For more information visit www.bluffcountrywoman.com/fossil-trail-created-by-se-mn-hbc-bluffcountryfossils-com.