MEXICO CITY, Mexico (AP) -- 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 that was ending 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 now lie deep beneath the sea, which during the Ice Age was hundreds of feet lower than now.

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.

Many academics argue that new discoveries, especially in South America, prove the Clovis people found existing inhabitants, who may have arrived by hop scotching past the northern ice fields in small boats.

Arturo Gonzalez said his team discovered at least three skeletons in caves along the Caribbean coast of Mexico's Yucatan Peninsula in 2001 and 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 that waters gradually seeped through the caves 8,000 to 9,000 years ago as Ice Age glaciers melted and sea level rose by about 400 feet worldwide.

Tests on charcoal found 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 radiocarbon years old -- which would translate to well over 13,000 calendar years.

If confirmed, "that would be the oldest" radio carbon date in the Americas obtained from a human bone, said archaeology textbook author Stuart Fiedel.

Fiedel, a defender of the "Clovis first" school, said the oldest estimate for the cave find still fits the Clovis time frame, though narrowly.

Larry Murphy, chief of the Submerged Resources Center for the U.S. 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."

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 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 water holes 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 404 yards into a cave, more than 65 feet 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 restudy 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.

Both discoveries would be significantly older than the skeleton known Kennewick Man -- 9,300-year-old paleoindian remains found by teenagers along a Washington state riverbank in 1996.

Until now, the Americas have produced only 25 bones or skeletons dated as more than 8,000 years old, said 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.

Copyright 2004 The Associated Press.