Fossil Hunter Finds 400 Million-Year-Old Worm Named After Oswego

OSWEGO, IL — A lifelong hobbyist fossil hunter recently presented the Oswego village board with a unique fossil. It's not the type of animal preserved - a minuscule worm-like creature - that makes it so; it's the fact that this particular animal is named after Oswego, and that the specimen is so well preserved after more than 400 million years in the earth. The fossil hunter who found the specimen - official name Tentaculites oswegoensis - is a Sugar Grove resident by the name of Tom Cesario. He said he was lucky to find it.

"It was 13 degrees out that morning... the next day I went back and the pile where I found [the fossil] was gone," Cesario said. "So I basically lucked out."

Cesario actually came upon the fossil last year in Oswego, on an offshoot of the Fox River called Waubonsee Creek. The creek saddled a construction site, and Cesario said he thought it might be possible that the construction actually unearthed the specimen. He added that after fossil hunting in the area his whole life, he immediately knew what the fossil was by its visual clues.

"When they were putting in the footings for the new buildings there in Oswego, they cut through that layer [of river soil]," he said. "By doing that, they put it all on the side, and I could tell exactly what [the fossil] was because it was a bluish-green color."

The coloration of the fossil indicated the mineral combinations present in it, and thus its approximate age. Tentaculites oswegoensis is from the Ordovician period, a time millions of years before the dinosaurs when most of what is now Illinois was the bottom of a shallow sea. The animal's exact taxonomy is still unknown, but in life it likely would have resembled modern flatworms or molluscs. It was first discovered sometime in the late 1800s, after the incorporation of Oswego in 1855. There are recorded mentions of it in academic articles dating to 1877.

"It's been out there for a hundred years," Cesario said. "It's just, no one collects it because it's very insignificant."

For something insignificant, Cesario's find has generated more attention from the media than he expected, including an article in the Chicago Sun-Times. He said he only gave it to the Oswego village board because he thought it was "pretty cool" and because he remembered the animal was named for the village; he did not anticipate being called up by reporters for it.

"I figured [the village board] would like it because it was named after the town," he said. "Boy, it went nuts."

But while this find may have pushed him into the media spotlight, Cesario said it was far from the first fossil he has found. Now retired from his former work as a fire system inspector for the military, Cesario said he has been looking for fossils since he was a child.

"I've just been collecting fossils since I was five years old," he said. "I got a wife that's put up with it for the last 46 years."

Cesario is also a member of the Chicago Area Paleontological Society, a group he described as "just a bunch of guys that get together every so often that collect fossils." He said he personally prefers to hunting for invertebrates - animals without backbones, like molluscs and insects - because looking for larger creatures is often legally difficult. Since 2009, the federal Paleontological Resources Preservation Act has made taking most vertebrate fossils from federal or Native American lands without authorization a crime punishable with fines and jail time.

"Mainly I stay with the invertebrates because when you start collecting the vertebrates... you can get in trouble with the government," Cesario said.

For young fossil hunters or aspiring paleontologists who want to investigate the deep past despite the limitations in place, Cesario said to "get out as much as [you] can."

In the marshy river systems of northeast Illinois, it seems there's always something new - and very old - to find.