Brendan Fenerty

S. Joy

Brendan Fenerty

DC Fisher, Univ. Michigan Museum of Paleontology

J. Halligan

Courtesy of CSFA

A. Burke, courtesy of CSFA

J. Halligan

The key to uncovering America's ancient past lies underwater. In the waning centuries of the last Ice Age, many of the favorite hunting grounds and camps of early Americans were flooded with waters unlocked from the melting polar ice. But now, thanks to SCUBA-diving archaeologists, a clear picture is emerging of the peoples who came to the Americas by boat—thousands of years before the Clovis peoples (who became the ancestors of today's Native Americans). In a deep sinkhole beneath Aucilla River in Florida, some of the most intriguing evidence to date for these pre-Clovis peoples has been carefully excavated—using specialized underwater exploration rigs. Scientists have discovered an incredibly rare 14,550 year-old hunting site, complete with stone tools, a slaughtered mastodon, and hints of canine companions who might have helped with the hunt.

Called the Page-Ladson site, the sinkhole is one of only a handful of pre-Clovis sites ever discovered, and it dates to roughly the same time period as similar sites such as the Paisley Caves in Oregon and Monte Verde, Chile. It’s also the oldest evidence of human occupation ever found in the US southeast, and it offers solid proof that humans lived throughout the Americas nearly 15,000 years ago, long before routes into the Americas from the Bering Land Bridge were ice-free. This adds further evidence to the idea that these people’s ancestors arrived by boat from the coasts of Asia, likely after thousands of years of migratory wandering.

Another crucial piece of evidence from Page-Ladson has to do with the slaughtered mastodon. It’s not clear whether humans killed the mastodon or simply scavenged a dead body, but markings on the bones and tusks show clear signs of butchery with the stone tools preserved at the site. Careful analysis of the sediment layers in the lakebed revealed that the sinkhole was once a pond, likely a popular watering hole for migrating mastodons—and the hunter-gatherer humans who followed the herds. As the researchers put it, these humans were fairly sophisticated hunters, memorizing the seasonal terrain of their prey and possibly even enlisting the help of dogs.

Once the researchers began dating the sediments in the sinkhole, they found something truly exciting. Humans and megafauna like mastodons co-existed for at least 2,000 years in the Americas—a fact that paleontologists had long suspected but lacked direct evidence for. At the Page-Ladson site, they found their evidence in the form of mastodon dung. More specifically, it came from a fungus that lives on mastodon dung. Researchers dug through each layer of sediment in the sinkhole for remains of the fungus; as they moved upward through the layers and forward in time, they found less and less of it. Finally, in a layer that had been dated to about 12,600 years ago, there was virtually none. So mastodons were visiting this watering hole for at least 2,000 years after this slaughter took place. As archaeologist Daniel Fisher put it during a press conference about the discovery, “That means that however humans and mastodons interacted, it took at least two millennia for the process of extinction to run to completion.”

Co-principle investigator Jessi Halligan explained how the group conducted their underwater investigation over a period of two years:

During our underwater excavations, we dug much as archaeologists do on land, teams of two divers would carefully remove all sediments in controlled levels by trial and by hand, vacuuming these sediments to the surface with the water dredge where all materials [were sorted] in floating screens. The Aucilla River is a blackwater river, meaning that we needed light which we mounted to caver's helmets to focus on our excavation areas. We used underwater lasers to control our depth of excavation, all of which allowed us to be very precise and to see items as we exposed them in place.

What’s ironic is that these discoveries could have been announced nearly 30 years ago in the 1980s. At that time, Halligan said, a diver named Buddy Page found the sinkhole and reported it to local paleontologists. The scientists did an excavation, locating tools and some mastodon bones. The team successfully dated those artifacts to 14,550 years ago. But at that time, the scientific community didn’t accept the idea that anyone had populated the Americas before the Clovis peoples crossed the Bering Land Bridge roughly 12,000 years ago. It’s only now, in the wake of many more pre-Clovis discoveries, that we can appreciate the Page-Ladson site for what it is: a record of America’s earliest humans, living among animals who vanished along with the pre-Clovis way of life.

Science Advances, 2016. DOI: 10.1126/sciadv.1600375 [Full text here]