A mysterious, Stonehenge-like structure beneath Lake Michigan has revealed new clues that could reshape our understanding of early human history in North America.

Discovered in 2007, the 9,000-year-old site lies 40 feet below the surface of Grand Traverse Bay and features large stones arranged in a line culminating in a hexagon, near a boulder bearing what was long suspected to be an animal carving.

Now, nearly two decades later, scientists have confirmed that carving to be a mastodon, an Ice Age species that went extinct more than 11,000 years ago.

Experts believe the relief served as a time marker, dating the structure to around 7000BC using sonar technology. 

That would make it one of the earliest known examples of prehistoric art on the continent, and strong evidence that ancient humans were engaging in symbolic expression far earlier than the previously accepted timeline of 4,000 years ago.

Researchers also identified two massive granite rings, roughly 40 and 20 feet across, connected to the line of stones that run for more than a mile across the lakebed.

The new findings suggest the site held significant importance for ancient peoples, as the dual granite rings, deliberately arranged stones, and carved prehistoric animal all point to a ceremonial, practical function, or possibly both. 

Dr John O’Shea from the University of Michigan believes that the stones served as a drive lane to direct large animals to the specific area where they could be killed, a practice characteristic of prehistoric cultures. 

While Lake Michigan is the second-largest of the Great Lakes, it would have been dry land or part of a wetland when the stones were erected.

The Stonehenge was discovered by researchers searching for a lost shipwreck on the bottom of Lake Michigan. England's Stonehenge is about 1,500 years old, making the structure found beneath the US lake much older.

Dr Mark Holley, an adjunct professor of Anthropology at Northwestern Michigan College who made the discovery, said the structure appeared to be a carefully arranged set of granite stones, some weighing as much as 2,000 pounds.

When Holley and his team first set eyes on the mastodon carving they were amazed, but knew such a discovery would need to be verified.

Many experts suggested the design was just cracks in a rock, but new scans of the rock prove otherwise.   

The rock is about 3.5 feet tall and five feet across, and the carving shows the side of a mastodon with a long trunk and tusks.

Earlier this year, a team from Northwestern Michigan College used advanced underwater imaging technology to fully map the site and uncover its true size. 

These scans replaced the original grainy sonar images taken in 2007, which had shown a rough line of stones but did not reveal the rings or the full layout of the sit

Archaeologists said that the discovery could challenge the established timeline of North America's early human activity, which has long centered on the Clovis culture, a Paleo-Indian group believed to have arrived around 13,000 years ago. 

The Clovis culture is significant because it represents one of the earliest, if not the earliest, widespread cultural complexes in North America, characterized by distinctive stone tools and a hunting lifestyle focused on megafaunal. 

Later this summer, Holley's team will return to extract sediment cores around the site to confirm exactly when rising lake levels buried it underwater.

If the stones were placed when the land was dry, this would confirm human activity thousands of years earlier than previously proven in this part of North America.

It would also suggest that organized human societies existed in the Great Lakes region during the early Holocene, building large-scale structures long before cities, writing, or agriculture appeared elsewhere.