Missing: The dinosaurs of Illinois

We have no reason to doubt that dinosaurs once roamed our state, so why haven’t we found any here?

Illinois is rich in fossils. Just poke around a pile of native rocks, and chances are pretty good that you’ll find a few. Unfortunately, any fossils you find won’t come from dinosaurs. Why not? Because a giant chunk of time is missing from the fossil record in the bedrock underlying our state.

Dead plants and animals can be transformed into fossils only under special conditions. One of the best ways for this to occur is by rapid burial in water laden with sediment—usually in rivers, lakes, and seas. Over thousands of years, layers of sediment build up and eventually become compressed into solid rock, preserving dead organisms within as fossils.

But during the Age of Dinosaurs, or the Mesozoic Era, Illinois was higher and dryer than it is now. The Great Lakes didn’t exist yet. So at the time, only a small amount of bedrock formed in Illinois, and almost all of that material eventually eroded away.

The western and eastern parts of the U.S. were lower and wetter during the Mesozoic Era, and the moist conditions favored the formation of fossils in those regions.

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