A team of Florida State University researchers has discovered stone tools alongside mastodon bones in Florida, revealing that humans settled in the southeastern U.S. as much as 1,500 years earlier than previously believed.

The tools and bones were found on the Aucilla River, which is now the oldest known region of human life in the southeastern U.S., dating back 14,550 years.

"This is a big deal," said Jessi Halligan, a professor at Florida State University and first author of the study. "There were people here. So how did they live? This has opened up a whole new line of inquiry for us as scientists as we try to understand the settlement of the Americas."

During the study, which took place between 2012 and 2014, Halligan and her team excavated the Page-Ladson site located around 30 feet underwater in an Aucilla River sinkhole.

Back in the 1980s and 1990s, several tools and a mastodon tusk were retrieved in a layer that was more than 14,000 years old. However, the findings were largely ignored due to their existence underwater and the belief that they were too old to be real.

After going back for a second look, the team discovered a biface - a knife with two sharp edges used for butchering animals - as well as numerous other tools. Comparison to the mastodon tusk from the previous excavations revealed signs of cutting. These cuts suggest that it might have been used by early humans to gain access to the tissue at the base of the skull for food.

"Each tusk this size would have had more than 15 pounds of tender, nutritious tissue in its pulp cavity, and that would certainly have been of value," said Michael Waters from Texas A&M University and co-author of the study. "Another possible reason to extract a tusk is that ancient humans who lived in this same area are known to have used ivory to make weapons."

The team used radiocarbon dating techniques to reveal that all of the artifacts date to about 14,550 years ago. Previously, the first inhabitants of the Americas were believed to have settled the area around 13,200 years ago.

"The new discoveries at Page-Ladson show that people were living in the Gulf Coast area much earlier than believed," Waters said.

"It's pretty exciting," Halligan added. "We thought we knew the answers to how and when we got here, but now the story is changing."

The findings were published in the May 13 issue of the journal Science Advances.