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Illinois' Monster: A Creature From The Past

Illinois was once home to one of the most interesting and confusing animals — the Tullimonstrum gregarium, known as the Tully monster. You would have to travel back 300 million years to see it alive! Today, everything we know about this sea creature we learned from fossils.

What a Tully monster would have looked like swimming in the ocean. (Photo via Shutterstock)

A very different world

Illinois looked very different 300 million years ago. It sat at the equator, clumped together with all the other continents. It was swampy. It was hot. The land was covered in thick forests. It probably looked more like the Amazon, with towering trees, 8-foot long millipedes and giant dragonflies.

Northeastern Illinois was right on the edge of a huge inland sea. The water was a mix of salt water and freshwater. This is called an estuary, and this is where the Tully monster swam.

One odd animal

Tully monsters look weird. Their body is tube-shaped, like a torpedo. Their eyes stick out on each side of their body on stalks. Where you would think the mouth would be there is a joined, trunk-like snout ending with a toothy claw. They could grow to be a little longer than a ruler, topping out at 14 inches, with a vertical tail fin and a long narrow dorsal fin.

Even more bizarre is that scientists can’t agree what kind of animal a Tully monster is. Is this water-lover a vertebrate (with a backbone) like us and other mammals, birds, reptiles and fish? Or is it an invertebrate (without a backbone) like crabs and other crustaceans, insects and octopuses? In 2016, scientists were positive that they proved it was part of the lamprey fish family and had a backbone. But by 2019, a new group of scientists said they found evidence that Tully monsters are invertebrates. There is still a lot to learn.

Mr. Tully’s monster

A Tully monster fossil. (Photo via Shutterstock)

How was it discovered? In the 1950s, Francis Tully of Lockport spent lots of time hunting for fossils in mines near Braidwood. He came across a fossil he had never seen before, and he brought it to the experts at the Field Museum. They had never seen anything like it either! Soon people began calling it Mr. Tully’s monster. Don’t take offense. In this case, monster just means something extraordinary. It certainly is!


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