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On Thursday, a team led by archaeologist James Chatters reported in the journal Science that they'd found a big piece of the puzzle: the most complete skeleton of such antiquity ever found in the Americas, between 12,000 and 13,000 years old. The skeleton contains both the craniofacial features of ancient Paleoamericans and mitochondrial DNA possessed by latter-day Native Americans.
he skeleton, dubbed "Naia" (an ancient Greek name related to water nymphs) by her discoverers, belonged to a teenage girl who fell more than 100 feet to her death nearly a half mile inside an elaborate network of karst caves that were largely dry at the end of the Pleistocene. Divers who found Naia in the cave on Mexico's Yucatán Peninsula named her watery grave Hoyo Negro ("Black Hole" in Spanish).
Without any bone collagen for radiocarbon dating, the team triangulated the skeleton's age by determining the age of calcite crystals known as "florets" growing on the bones, carbon-dating nearby bat guano, and carbon-dating Naia's tooth enamel.
Chatters speculates that ancient Americans' morphology may have changed as their living conditions changed. As highly mobile hunter-gatherers became more settled, evolutionary processes may have selected for more domestic traits and temperaments, resulting in the softer, rounder features seen in the faces of Native Americans.
"You start seeing these more domestic forms when females have more control over the food supply, when they're not so dependent on aggressive men," Chatters said. He added that this process of neotenization—the retention of some juvenile traits—can be seen in populations across the Northern Hemisphere between the late Pleistocene and modern times.
Speculation about the potential drivers of evolutionary change is not part of the team's study.
the team triangulated the skeleton's age by determining the age of calcite crystals known as "florets" growing on the bones, carbon-dating nearby bat guano, and carbon-dating Naia's tooth enamel.