What the Fossils Tell Us: Iowa Comes to Life


What did the Iowa plant and animal landscape look like 12,000 years ago, when the first humans began to arrive? Iowa State experts paint a picture of that time period:
“The landscape was changing from a tundra toward perhaps an oak savanna type of environment,” Matt Hill, ISU associate professor of anthropology, says. “The environment was drying out and warming up; the Ice Age animals – mammoths, giant beavers, mastodons, giant sloths – were teetering on extinction. There would have been camels, stag-moose, and bison” in this area.
“Plants would have been very cold-tolerant,” Hannah Carroll, ISU PhD candidate in the Department of Ecology, Evolution & Organismal Biology, adds. “You would have seen mosses, then lichens, then small flowering plants, with shrubs and trees appearing last. It would have eventually been dominated by a prairie ecosystem.”

Under the sea
Though Iowa today is firmly landlocked, it once was submerged beneath warm, shallow seas.

Inland seas have advanced and retreated over Iowa many times since the late Cambrian, about 500 million years ago. Portions of Iowa were last under water during the Cretaceous Period, which ended 66 million years ago.

At different points in Iowa’s geologic history, Iowa was a coastal area or completely submerged beneath the water. During the Mississippian and Devonian periods, Iowa was a center for diverse marine life. In fact, most rocks under the state’s glacial sediment are marine rocks, and many marine fossils can still be found today in Iowa.

Two areas are worth noting: the Devonian Fossil Gorge in Johnson County near Iowa City, and the Fossil and Prairie Park Preserve in Floyd County near Rockford.

Fossils were first exposed at the Devonian Fossil Gorge following the great flood of 1993. During that event, floodwaters swept away a campground and picnic facilities and first exposed the rocks of the gorge. Subsequent floods have widened the gorge and swept away loose rocks and vegetation to expose additional rocks and fossils.

Further north, in Floyd County, the Fossil and Prairie Park Preserve is a fossil hunter’s
paradise. The former brick and tile quarry is home to brachiopods, cephalopods, crinoids, and corals, remnants from 375 million years ago when the shallow seas covered Iowa.

“This park is a really unusual resource for the public,” Jane Pedrick Dawson (’83 geology, MS ’86), ISU senior lecturer in geological and atmospheric sciences, says. “Most parks in the country prohibit you from collecting anything, and here’s a park that encourages you to get down on your knees and start sifting through the sediment and pull out the brachiopods and crinoids and other fossils and take them home. I can’t think of any other place where the public is encouraged to collect fossils and take them home.”

Another related resource in Iowa is the University of Iowa’s Museum of Natural History. The museum has an exhibition showing a Devonian Coral Reef from 380 million years ago. Just recently, on the University of Iowa campus, a construction crew dug up 385-million year-old coral fossils while working on the expansion of one of the university facilities.

fossils3In other “weird science” news, geologists at the Iowa Geological Survey recently found exceptionally preserved fossils from the Decorah Impact Structure in Winneshiek County, about 60 feet under the Upper Iowa River. It turns out that the fossils came from a 460-million-year-old predatory water bug said to be as big as a human. The creature, named Pentecopterus decorahensis, was a sort of sea scorpion that grew to 5 feet 7 inches with a spike tail and a dozen claw arms sprouting from its head.


Matt Hill finds artifacts in Ledges State Park. Photo by Jim Heemstra.

A state filled with game
When European settlers arrived in what is now Iowa, the state was full of game; there was an abundance of wildlife. Truly, the biodiversity was greater than most people would expect.

More than 450 species lived and bred in Iowa when Europeans arrived, including 68 species of mammals, 186 species of birds, 45 species of reptiles, 21 species of amphibians, and 136 species of fish. An even greater variety of insects, other invertebrates, and plants were found in the state. According to A Country So Full of Game by James L. Dinsmore, several thousand species of plants and animals once occupied Iowa.

Today, a number of those species have become extinct in Iowa or have become threatened or endangered.

Some of the species the European settlers would have encountered included bison, elk, white-tailed deer, black bears, wolves, coyotes, foxes, bobcats, mountain lions, muskrats, otter, beaver, mink, passenger pigeons, prairie chickens, wild turkeys, quail, ruffed grouse, cranes, shorebirds, and waterfowl.

Of course, most of the Ice Age animals had already died out: the stag-moose, mastodon, mammoth, giant sloth, and the like.

It’s not uncommon for Iowans to uncover the bones of extinct animals, especially after a flood. Just walking through the creek at Ledges State Park in Boone County during our photo shoot, Matt Hill, ISU associate professor of anthropology, found a small bone fragment.

“Ledges has 12,000 years of history,” Hill says. “The stream scours out the remnants of buried materials. Everything buried was once on the surface.”

Hill says people bring him fossilized remains to identify every month. Often the bones turn out to be from a recent, domesticated species. But sometimes he hits the jackpot.

“It’s not what we find, from my perspective. It’s what we find out.”

SIDEBAR: The Dinosaur debate
Did dinosaurs live in Iowa? Well, it depends on whom you ask.

The Iowa Geological Survey website says: “Did dinosaurs once live in Iowa? The simple and unqualified answer is, ‘Yes, without a doubt!’ But the actual evidence for dinosaurs in Iowa is limited to only a few fossils. Dinosaur fossils have been found in several states adjoining Iowa (Nebraska, Minnesota, Missouri, South Dakota), and wandering dinosaurs would have been unimpeded by those artificial boundaries.”

And in the book Iowa’s Geological Past, author Wayne L. Anderson says: “Evidence for dinosaurs in the state is scant, consisting of a single bone fragment from Guthrie County. [Researchers] tentatively identify the bone as dinosaurian based on its size and microscopic structure.”

Not so fast, says Matt Hill, ISU associate professor of anthropology. “It needs to be made clear that there were no dinosaurs in Iowa,” he says, adding, “Don’t believe everything you read.” He cites the confusion of a recent find, a fossil that was first thought to have come from a sea reptile but eventually was determined to have come from…a horse.

“In short, to say the dinosaur record in Iowa is scant is an overstatement,” he says. “It consists of one very small piece of suspected dinosaur bone from a stream.”

To wit: “No dinosaur fossil has yet been firmly identified from Cretaceous strata anywhere in the state of Iowa,” according to a 1996 field guide to the Cretaceous of Guthrie County written by Larry J. Wilson, Iowa Department of Natural Resources.

However, the author goes on to say that the bone fragment found in the Guthrie County gravel pit is possibly a dinosaur fossil, and “it is hoped that some diligent or exceptionally lucky collector will one day produce an identifiable bone.”

And so the debate continues. Stay tuned.

SIDEBAR: Moose in our midst
The little-known stag-moose, an Ice Age animal, lived in Iowa as far back as 30,000 years ago and went extinct just under 10,000 years ago. Matt Hill, ISU associate professor of anthropology, has specimens of these unique animals in his Curtiss Hall office on campus.

He holds up one antler, found in Parkersburg, that he radiocarbon dated to be between 12,600 and 12,800 years old. He picks up another, found by a retired game warden in western Iowa. Another, found in the 1970s by a gravel pit operator in Polk County and currently on display at the State Museum in Des Moines, is thought to be about 30,000 years old.

“I just got really lucky, dating that old one [and then this young one],” Hill says. “The number of directly dated stag moose in the country – there are only a handful. They’re unusual.”

He says the stag-moose – which had the body of a moose, the face of an elk, and an antler rack like neither – were here before glaciers covered central Iowa, and they returned for a short time after the glaciers retreated. The age of the most recent specimen suggests that these animals lived at the same time as the earliest known humans in the area.


This article was originally published in VISIONS magazine. To receive the full issue delivered to your mailbox four times per year, become a member of the ISU Alumni Association.


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