アメリカ最古の人骨が水中遺跡から発見

メキシコ・カンクーンの近くにある町、テゥルムでアメリカ大陸最古となる可能性の人骨(女性）が発見されたそうです。ナショナル・ジグラフィックから発表されています。まだ精密な調査がもう少し必要だそうですが、炭素年代で１３，６００年前と出ています。

この人骨は水中洞窟の中から発見されたそうです。水深約１５ｍの地点ですが、当時は海底面が低かったので陸だったそうです。彼女は東南アジアか北アジア系に骨格の特徴が似ているそうです。

Deep inside an underwater cave in Mexico, archaeologists may have discovered the oldest human skeleton ever found in the Americas.

Dubbed Eva de Naharon, or Eve of Naharon, the female skeleton has been dated at 13,600 years old. If that age is accurate, the skeleton—along with three others found in underwater caves along the Caribbean coast of the Yucatán Peninsula—could provide new clues to how the Americas were first populated.

The remains have been excavated over the past four years near the town of Tulum, about 80 miles southwest of Cancún, by a team of scientists led by Arturo González, director of the Desert Museum in Saltillo, Mexico (see map of Mexico).

“We don’t now how [the people whose remains were found in the caves] arrived and whether they came from the Atlantic, the jungle, or inside the continent,” González said.

“But we believe these finds are the oldest yet to be found in the Americas and may influence our theories of how the first people arrived.”

In addition to possibly altering the time line of human settlement in the Americas, the remains may cause experts to rethink where the first Americans came from, González added.

Clues from the skeletons’ skulls hint that the people may not be of northern Asian descent, which would contradict the dominant theory of New World settlement. That theory holds that ancient humans first came to North America from northern Asia via a now submerged land bridge across the Bering Sea (see an interactive map of ancient human migration).

“The shape of the skulls has led us to believe that Eva and the others have more of an affinity with people from South Asia than North Asia,” González explained.

Concepción Jiménez, director of physical anthropology at Mexico’s National Institute of Anthropology and History, has viewed the finds and says they may be Mexico’s oldest and most important human remains to date.

“Eva de Naharon has the Paleo-Indian characteristics that make the date seem very plausible,” Jiménez said.

Ancient Floods, Giant Animals

The three other skeletons excavated in the caves have been given a date range of 11,000 to 14,000 years ago, based on radiocarbon dating.

Radiocarbon dating measures the age of organic materials based on their content of the radioactive isotope carbon 14.

According to archaeologist David Anderson of the University of Tennessee, however, minerals in seawater can sometimes alter the carbon 14 content of bones, resulting in inaccurate radiocarbon dating results.

The remains were found some 50 feet (15 meters) below sea level in the caves off Tulum. But at the time Eve of Naharon is believed to have lived there, sea levels were 200 feet (60 meters) lower, and the Yucatán Peninsula was a wide, dry prairie.

The polar ice caps melted dramatically 8,000 to 9,000 years ago, causing sea levels to rise hundreds of feet and submerging the burial grounds of the skeletons. Stalactites and stalagmites then grew around the remains, preventing them from being washed out to sea.

González has also found remains of elephants, giant sloths, and other ancient fauna in the caves.

(Learn more about how caves form.)

Human Migration Theories

If González’s finds do stand up to scientific scrutiny, they will raise many interesting new questions about how the Americas were first peopled.

Many researchers once believed humans entered the New World from Asia as a single group crossing over the Bering Land Bridge no earlier than 13,500 years ago. But that theory is lately being debunked.

Remains found in Monte Verde, Chile, in 1997, for example, point to the presence of people in the Americas at least 12,500 years ago, long before migration would have been possible through the ice-covered Arctic reaches of North America.

(Related: “Clovis People Not First Americans, Study Shows” [February 23, 2007].)

Confirmation of Eve of Naharon’s age could further revolutionize the thinking about the settlement of the Americas.

This September, González will begin excavating the fourth skeleton, known as Chan hol, which he says could be even older than Eve.

The Chan hol remains include more than ten teeth, which will allow researchers to date the specimen and gather information about Chan hol’s diet.

“When we learn more about the [Mexican finds] we’ll be able to better evaluate them,” said Carlos Lorenzo, a researcher at the Universitat Rovira i Virgili in Tarragona, Spain, an expert on the subject who was not involved in the current study.

“But in any case, if it’s confirmed that Eva de Naharon is 13,000 years old, it will be a fantastic and extraordinary finding for understanding the first settlers of America.”

González said he and his team hope to publish the full results of their analysis after the excavation of the fourth skeleton.

“We’re not yet in the phase of research of determining how they arrived,” he said. “But when we have more evidence we may be able to determine that.”

引用元：http://news.nationalgeographic.com/news/2008/09/080903-oldest-skeletons.html