I sat on the tan, dusty ground of the quarry in north central Iowa, fingers grasping at the shell that lay halfway buried in the chalky clay and limestone. Wiggling it back and forth, I gently pulled it up from the ground that it had been resting in for millions of years. The ridged shell was almost perfectly intact, painting me a detailed picture of what the animal looked like. I had found a brachiopod fossil, a marine invertebrate who used to live in the warm, shallow sea of the Devonian Period, roughly 380 million years ago. As I sat examining my find, I couldn’t help but think about how special it is to find something so ancient, to hold the remnants of their life in my hand, and glimpse what life on Earth was like millions of years ago.
 |
| Ridged brachiopod fossils with intricately preserved detail. Photo by Heaven Walker. |
While Iowa may currently be land locked, if we were to travel back in time to the Devonian Period, Iowa would be found near the Equator and beneath a warm, shallow sea. This ancient environment supported a vast number of marine invertebrate species who lived along the sea floor. Snails and trilobites roamed through bunches of corals, brachiopods, and crinoids, all while cephalopods and fish ruled the waters above.
I can imagine the seabed, littered with solitary brachiopods as they slowly opened and closed their shells while filter feeding, much like their modern day descendants. Brachiopods contributed to the mosaic of diversity along the sea floor, with different species toting different shell shapes and sizes that help to classify their fossilized remains today. I can imagine the crinoids, also known as sea lilies, with their long, segmented stalks and flower-like head, or calyx, waving in the current. As filter feeders, their feathery arms on the calyx would have been gathering up food particles and directing them towards their mouth.
The disked segments of the stalk are the most commonly found remains of the crinoids who once inhabited the landscape. Also joining in on the filter feeding party of the Devonian Period were the horn corals. Their ridged, curved outer shell served as a protective layer for the soft-bodied polyp living inside. Small tentacle-like structures erupted from the top of the coral, filtering food out of the water. While looking at the horn coral fossil I can see the different segments of growth, etching their life in stone.
 |
| Horn coral (left) and a gastropod fossil (right). Photo by Heaven Walker. |
As these ancient marine organisms died, their shells, skeletons and other hard parts built up on the sea floor, providing calcite to the bottom of the sea. As layers built up, they became compacted and sedimented into the limestone that is now widely seen throughout Iowa. Because of the limestone bedrock, marine fossils can be found in many areas of the state. My eyes are almost always glued to the ground because of my time growing up in Iowa looking for fossils, and that habit follows me wherever I go.
However, I won’t be tracking down fossils here in the Northwoods. The shallow sea that blanketed Iowa during the Devonian Period did not reach where the Northwoods are today. Long before the Devonian Period, the bedrock of the Northwoods was gradually being elevated, creating the Wisconsin Dome. The shallow Devonian sea did not cover the height of the Wisconsin Dome, but rather resided in less elevated parts of southern Wisconsin. But in my mind, the Northwoods make up for their lack of marine fossils in rolling hills, swaths of forest to explore, and beautiful waterfalls. And even though I reside in the Northwoods fulltime now, I cherish the opportunity to return to my roots and dig up fossils in Iowa.
For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. Our Summer Calendar is open for registration! Visit our new exhibit, “The Wetland Way". Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.
