Scientists have discovered what they say is the "oldest most complete" human skeleton in the Western hemisphere, the National Geographic Society reports.

The 12,000-year-old skeleton includes major bones, an intact cranium and a set of teeth. Naia, as the skeleton is named, was thought to be a girl around 15 or 16 years old when she died.

She was found among the remains of extinct animals — like sabertoothed cats and giant sloths — in Hoyo Negro, a flooded cave 130 feet below sea level on Mexico’s Yucatan Peninsula. Researchers used radiocarbon dating of tooth samples and the surrounding animals to estimate Naja's age.

Image: Paul Nicklen/National Geographic

A team of 16 divers, archaeologists and paleontologists documented the find with video in the water.

Researchers say the discovery shows evidence of a connection between Paleoamericans, who lived on the continents after the last ice age, and modern Native Americans.

The discovery will be featured in National Geographic Magazine and in a PBS documentary in 2015. In the meantime, preliminary findings are published in the journal Science.