Rebecca Young: Considering Brown County’s prehistoric roots in rainy spring

Spring equinox is behind us, and it’s flood season. Across North America snow is melting, rivers are thawing, and storm drains are overflowing. Here in Brown County, we’re all familiar with seeing fields full of water, power lines tilting toward temporary ponds, and signs indicating creeks flowing over the road. For a land-locked state, rising water can be a big part of our spring time.

Spring floods always remind me that the land we now call Indiana wasn’t always hills and forests far from the sea.

In the Devonian era (about 390 million years ago), the land that is now Indiana was a shallow sea, called the Illinois Basin that covered Illinois, Indiana and western Kentucky and connected to a larger, deeper Rheic Ocean that covered most of the planet.

This was before the arrival of flowering plants, reptiles, or mammals. The oceans were where the good stuff was happening.

It was a world of fishes and sharks. And the shallow seas of Indiana teemed with interesting life. These warm seas were homes to large coral reefs and the first fossil ammonites are from this period.

Just south of here, in Falls of the Ohio State Park are some of the best exposed fossil beds from this time period. The fossils are mostly horn and honeycomb corals.

The major predators of these reefs were the placoderms, or armored fishes. Their name reflects that they were covered in large bone plates, like the armor of a medieval knight, instead of the scales of later fish. These were also some of the first fish to have true jaws and they definitely used them to great effect. They didn’t have the rows of sharp teeth like a shark, but instead used bony plates to crush and tear their prey.

The largest of these, Dunkleosteus, was 30 feet long and is considered one of the first super-predators. The Dunkleosteus is the state fossil fish of Ohio and has been found all through the region, indicating that it certainly prowled the seas of Indiana in the Devonian.

Researchers estimate that it ate anything it wanted to, including smaller Dunkleosteus. If any schools or universities are looking for a good mascot, I would recommend the Dunkleosteus; the basketball cheers write themselves.

Some of the smaller creatures that swam away from the giant blade-mouthed super-fish were lobe-finned fishes. Lobe-finned fishes have chunky fleshy fins, while modern fish are mostly ray-finned fishes, with the thin paddle-fins that we’re used to seeing on the bluegills and bass of our lakes and rivers.

Only a few lobe-finned fishes remain, mostly living in warm waters near Madagascar and Indonesia. But in the Devonian they were common throughout the shallow seas.

Some lobe-finned fishes gave rise to a creature called Tiktaalik that is the earliest known tetrapod, a group that includes birds, mammals, reptiles and amphibians.

Tiktaalik had strong hind limbs and could lift its head out of the water and begin to consider moving to drier climates.

So as the rain pours down and the spring peepers climb the window and screens of our homes, remember that we all live on lands formerly warm reefy bathwater-seas filled with giant hunter fish the size of school buses.

And when you feel like the spring rains are making you an aquatic creature, you can also use your tetrapod neck joints to lift your head up and think about the drier times coming soon.

Rebecca Young is descended from some of the original land grant settlers of Brown County and has in the county on and off for four to five years. She comes back often to visit her parents who are Brown County residents. Young is a Phd biologist who spent about 15 years working with birds in Indiana, Kentucky, Alaska, Norway, Sweden, North Dakota, Mexico and more. She also studied physiology and ecology, and has published scientific papers and book chapters. Send comments to [email protected].