The stone tools and mastodon bones uncovered in Aucilla River in Florida reveal that humans settled in southeastern United States 1,500 years earlier than thought. The findings, published on May 13 in the journal Science Advances, included a bitface, a sharply-edged knife used for cutting and butchering animals and signs of cutting at the mastodon tusks.

“This is a big deal,” says Jessi Halligan, an assistant professor of anthropology at Florida State University. “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.”

The researchers dug up the Page-Ladson site which is 30 feet (nine metres) underwater in a sinkhole in the Aucilla River. This Florida river is now the oldest site of life in the southeastern US so far, dating back to 14,550 years.

Apparently, the stone tools and a mastodon tusk were found in a layer more than 14,000 years old during the 1980s and 1990s. Nevertheless, the discovery was overlooked and thought to be inauthentic because these artifacts were too old and were found in an unlikely place.

Between 2012 and 2014 the researchers took another look at the excavated objects. Using radiocarbon techniques, the research team realised that the objects belonged to humans who settled in the area 1,550 years earlier than previously thought. The researchers believe that the tusk could have had a big chunk of tender, nourishing meat. The ivory could have also been used to make weapons or cutting tools.

“It’s pretty exciting,” points out Halligan. “We thought we knew the answers to how and when we got here, but now the story is changing.”

Previously, a group of humans called Clovis was believed to be among the first humans to settle in the Americas. Scientists claim that these people inhabited the area about 13,200 years ago.