The structure, according to University of Tennessee paleobiology professor Colin Sumrall, was a 475-millon-year-old fossil belonging to an extinct sea creature known as a trilobite.
"Typically when we look at fossils of trilobites, they molt when they grow," Sumrall told ABC affiliate WATE.com. "So what happens is, the trilobite skeleton just crumbles into hundreds of little pieces. To find one where all the pieces are intact, it's actually a pretty lucky find."
According to Fossilera.com, trilobites comprised one of the earliest known groups of arthropods and thrived throughout the Paleozoic era with more than 600 species.
For nearly 300 million years, the sea creatures resembling modern horseshoe crabs scoured the oceans.
Sumrall said he could imagine Ryleigh as a great paleontologist one day.
"I can show kids that are my age that they don't have to sit inside and play games. They can actually go outside and find different things," Ryleigh told WATE.
She hopes the fossil will be displayed in a public museum for all to enjoy.
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