Mexico City - Divers making dangerous probes through underwater caves near the Caribbean coast have discovered what appears to be one of oldest human skeletons in the Americas, archaeologists announced at a seminar on Friday.

The report by a team from Mexico's National Institute of Anthropology and History exploits a new way of investigating the past. Most coastal settlements by early Americans are deep beneath the sea, which during the Ice Age was hundreds of metres below its current level.

Researchers at the international "Early Man in America" seminar here also reported other ancient finds - including a California bone that is a rival for the title of the oldest in the Americas.

The discoveries fall close to the start of the time that traditional theories say a so-called Clovis culture could have moved from Asia to Alaska over a temporary land corridor that began to open about 13 500 years ago.

'It's something that I had been dreaming of for many years'
Many academics argue that new discoveries, especially in South America, prove that the Clovis people found existing inhabitants, who may have arrived by hopscotching past the northern ice fields in small boats.

Arturo Gonzalez said his team had discovered at least three skeletons in caves along the Caribbean coast of Mexico's Yucatan Peninsula in 2001 to 2002. Photos showed two remarkably well preserved.

"It's something that I had been dreaming of for many years," said Gonzalez, 39, who has combined diving and research since he was a teenager. "To find a person who had walked those caves was like a treasure."

Gonzalez said the bones must date from before the time waters gradually seeped through the caves 8 000 to 9 000 years ago as Ice Age glaciers melted and sea level rose by about 120m worldwide.

Tests on charcoal beside one female skeleton would place it at least 10 000 years ago. An expert at the University of California, Riverside, dated it as 11 670 radio-carbon years old - which would translate to well over 13 000 calendar years once corrected for varying quantities of atmospheric carbon over the millennia.

'It is pioneering in an international sense'
If confirmed, "that would be the oldest" radio carbon date in the Americas obtained from a human bone, said archaeology textbook author Stuart Fiedel, a defender of the "Clovis first" school.

Fiedel said the oldest estimate for the cave find still fits the Clovis time frame, though narrowly.

Brazilian researchers say they have found a tooth that was radio carbon tested to 13 500 years, which would make it even older in calendar years, though some US archaeologists view the report skeptically. If confirmed, it would seem to rule out "Clovis first",

Larry Murphy, chief of the Submerged Resources Center for the US National Park Service, said in a telephone interview that the Mexican exploration was "one of the first systematic studies of human materials associated with a submarine cave."

"It is pioneering in an international sense," he said.

The discovery helps prove that humans inhabited the Yucatan at least 5 000 years before the famed Maya culture began building monuments at sites such as nearby Tulum.

Gonzalez said the skeleton did not appear to be Mayan, but with no tools yet found, almost nothing yet is known of those first inhabitants.

Gonzalez said cave divers had sometimes mentioned seeing skeletons and he convinced skeptical officials to finance a survey of the waterholes that dot the Yucatan, a limestone shelf.

Extensive, flooded caves wind off from some of those holes. Many were above ground during the Ice Age and Gonzalez speculated people may have used them as paths down to fresh water.

Gonzalez said the oldest find was made 367m into a cave, more than 20m below sea level during expeditions that can be extremely dangerous.

It took repeated trips to record the sites and excavate the bones, which then required two years of preservation.

Team co-director Carmen Rojas said the divers had 40 minutes to wind their way through the cave to the site, 20 minutes to work there and 40 minutes to swim back, followed by 20 to 60 minutes of decompression time.

"You train five years for those 20 minutes," she said.

Meanwhile, John Johnson of the University of California, Santa Barbara, said an elaborate re-study of a woman's femur found on Santa Rosa Island in California's Channel Islands established a calendar-year age of 13 200 to 13 500 years. It had been calculated at about 1 000 years less when found in 1959.

Remains of an infant in Minnesota have been dated to roughly the same period as has a skull found on a hill beside Mexico City's airport.

Until now, the Americas have produced only 25 bones or skeletons dated as more than 8 000 years old, according to Silvia Gonzalez of John Moores University in Liverpool, England.

But she told the conference that she would soon publish a paper establishing that humans occupied a site near Puebla east of Mexico City 21 000 to 28 000 years ago. - Sapa-AP