Divers carefully place a marker near a human skull found upside down in a large underwater cave near the Caribbean Sea on Mexico's Yucatán Peninsula in 2007.

Based on the skull's location, the team believes the remains ended up there about 10,000 years ago—just before the then dry cave was inundated as sea level began rising. If confirmed, that age would make the skull one of the oldest known remains of an early American, or Paleo-Indian.

Though the skull was found alongside bones of a mastodon and other prehistoric animals in 2007, news of the find was released only late last month, to allow time to properly document the site, train the divers in archaeological practices, and coordinate with authorities.

The divers had previously seen Ice Age animal remains in surrounding caves, but the human skull was a surprise. "That's one of the beauties of exploration—you never know what you're going to find," diver Alberto Nava said.

Now comes the tricky part. "We want to figure out the story of Hoyo Negro and how the human and animal remains got there," said Nave, of the Projecto Espeleológico de Tulum (PET) organization and Global Underwater Explorers (GUE).

During the 2007 expedition, divers descend into Hoyo Negro—"black hole" in Spanish.

"The name comes from the black holes in space," Nava explained. "When we first entered the place, it was just pitch black everywhere. We almost felt like it was absorbing our light.

"I think most people think of caves as something scary," he added.

"For us, it's a beautiful place. The caves are wide and decorated with stalactites. And the water is so crystal clear that when you look at your hand or your equipment, it looks like you're floating in air."

source: Nationalgeographic.com source: niburunews.com