Fossils Prove Illinois Used To Be Tropical

More than 300 million years ago, Illinois was a very different place. Instead of cornfields and prairies, the land lay in the tropics, teeming with swamps, rivers and shallow seas.

Today, that ancient world is preserved in the world-renowned Mazon Creek fossil beds, where researchers recently reexamined a massive collection of more than 300,000 fossils and uncovered a breakthrough. It turns out the area (near modern-day Coal City, Illinois) once hosted three distinct ecosystems, each with its own unique animal and plant life.

“This was a fun project that kind of came about in a weird way,” said Dr. Jim Schiffbauer, professor at the University of Missouri and a co-lead on the study.

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Oddly enough, the latest discovery got a helping hand from the coronavirus. Initially started by retired geologist Gordon Baird, who spent decades collecting Mazon Creek fossils across Illinois, the project got a fresh boost from a group of students stuck at home during the pandemic. The group, looking for creative ways to study paleontology virtually, set to work digitizing all of Baird's records.

When all that data landed on Schiffbauer’s desk, he and his team used modern statistical tools and mapping techniques to uncover something new.

“There are distinct ecosystems here, and actually more than what Gordon originally proposed.” Schiffbauer explained. “There is the freshwater, there is an estuary and then there is a fully marine ecosystem. So it's really neat.”

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The team’s analysis revealed a freshwater zone dominated by river fish, insects, and plants washed downstream; a brackish estuary with hardy, salt-tolerant clams and other bottom-dwelling animals; and an offshore marine setting rich in jellyfish.

That tropical setting may seem surprising for Illinois, but the continents once looked very different. “300 million years ago, North America was a little bit twisted and it was further south.” Schiffbauer said. “Southern Illinois would have been looking west.”

While the study doesn’t directly address climate change, Schiffbauer says the Carboniferous world of Mazon Creek holds important comparisons.

“It is kind of a parallel to where we're going, in terms of sea level and heat on the planet and increasing carbon dioxide in the atmosphere," he explained.

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For Schiffbauer, the work is both personal and professional, “The Mazon has always been on my bucket list," he admitted. "I'm optimistic that this is going to be the go-to paper for Mazon moving forward, because it really kind of summarizes and solidifies some of the previous interpretations, and adds more nuance to them."

Weather.com lead editor Jenn Jordan explores how weather and climate weave through our daily lives, shape our routines and leave lasting impacts on our communities.