(CNN)It's a discovery that could rewrite the story of southeastern United States.
Stone tools and mastodon bones found at the bottom of a Florida river point to humans living in the region 14,550 years ago. That's more than 1,500 years earlier than previously believed, scientists say.
"This is a big deal," said Jessi Halligan, one of the study's authors and an assistant professor of anthropology at Florida State University.
"It's pretty exciting. We thought we knew the answers to how and when we got here, but now the story is changing."
The discovery on the Aucilla River was reported Friday by the journal Science Advances.
Butchered bones, knives
The four-year study included sending divers to the Page-Ladson site, a deep hole 30 feet underwater in the Aucilla River, researchers said.
There, divers excavated artifacts such as butchered bones of extinct animals, a mastodon tusk and a biface, which is a knife fragment with sharp edges.
"At Page-Ladson, hunter-gatherers, possibly accompanied by dogs, butchered or scavenged a mastodon carcass at the sinkhole's edge next to a small pond at ~14,550," the authors said in Science Advances.
What was once a pond was buried beneath the murky waters for a series of reasons, including centuries of civilization, rising sea levels and layers of sediment.
"These people had successfully adapted to their environment; they knew where to find freshwater, game, plants, raw materials for making tools, and other critical resources for survival."
The scientists used radiocarbon dating techniques to find out how old the artifacts are.
What about the Clovis?
Until that point, researchers had believed the Clovis people were among the first inhabitants of the Americas about 13,000 years ago, according to the study. Page-Ladson is the first pre-Clovis site documented in the southeastern part of North America, it said.
"The new discoveries at Page-Ladson show that people were living in the Gulf Coast area much earlier than believed," said Michael R. Waters, director of Texas A&M's center for the study of the first Americans. Waters was one of the study's lead authors.
In the 1980s, other researchers had retrieved several stone tools and a mastodon tusk from the site, but their discovery did not make much news.
Halligan and her colleagues returned to the site in 2012 and expanded on the previous research and archaeological finds. In one of the instances, a mastodon tusk recovered earlier had deep grooves. They concluded the grooves were made by humans during the tusk's extraction.