The fossilized mysterious organism, roughly elliptical in shape with multiple lobes and almost 7 feet in length, was discovered near Covington, Ky., by Ron Fine of Dayton, a member of the Dry Dredgers, an association of amateur paleontologists based at the University of Cincinnati.
The club, celebrating its 70th anniversary this month, has a long history of collaborating with academic paleontologists, a university release said Tuesday.
"I knew right away that I had found an unusual fossil," Fine said. "Imagine a saguaro cactus with flattened branches and horizontal stripes in place of the usual vertical stripes. That's the best description I can give."
The fossil reminded him of streamlined shapes seen in coral, sponges and seaweed as a result of growing in currents of water, he said.
The find has professional paleontologists scratching their heads.
"It's definitely a new discovery," David L. Meyer of the University of Cincinnati geology department said. "And we're sure it's biological. We just don't know yet exactly what it is."
The mystery monster seems to defy all known groups of organisms, Fine said, and leave people with more questions than answers.