Alex Alvarez swims toward the human skull (lower right) his team discovered in the Hoyo Negro cave.
The skull's shape could offer new insights into where the first Americans migrated from, said Dominique Rissolo, an archaeologist at the Waitt Institute in La Jolla, California. (Waitt and National Geographic collaborate on a grant program.)
"By doing these kinds of analyses, we're able to get a better understanding of which Old World populations these individuals most closely resembled," said Rissolo, who's helping to organize a broader investigation of Hoyo Negro with Mexico's National Institute of Anthropology and History.
For now, though, the skull is still in the upside down position it was found in—the team hasn't touched or moved the remains.
Nava, the cave diver, said, "In any archaeological scene, the context that you find something in is key."
The team hopes at some point to extract a skull sample for testing, but that won't happen until a clear plan is in place.
"Right now our main objective is to protect what is there," Nava said,
"and to do the least amount of damage until we can figure out what we're going to do."
(Related: "Undersea Cave Yields One of Oldest Skeletons in Americas.")