LOS ANGELES, Jun 09, 2009 (Xinhua via COMTEX) -- U.S. and Canadian researchers on Monday claimed they had solved the mystery behind the Sharktooth Hill bone bed, the largest prehistoric marine fossil in the world.
The 10-to-50-centimeter-thick layer of fossil bones include shark teeth as big as a hand, turtle shells three times the size of today's leatherbacks, and bones from extinct seals and whales.
The researchers disproved the one-time catastrophe theory that the fossil bones were the result of a volcano eruption or a toxic algal bloom.
They also disproved the theory that the 100 sq km area had been a killing ground for megalodon, a 12-meter-long version of today's great white shark, when the ocean covered the southern end of the Central Valley of California about 15 million years ago.
Instead of a sudden die-off, the researchers said in the journal Geology that the bone bed, discovered in the 1850s, "is a 700,000-year record of normal life and death between 15 million and 16 million years ago."
"If you look at the geology of this fossil bed, it's not intuitive how it formed," said Nick Pyenson, a paleontologist from the University of British Columbia and a lead researcher on the project while he was studying at the University of California, Berkeley.
"We really put together all lines of evidence, with the fossil evidence being a big part of it, to obtain a snapshot of that period of time," Pyenson said.
He and U.S. paleontologists examined more than 3,000 fossilized specimens of bones and teeth and found only five indicating shark bites.
They also cut out a meter-square section of the bone bed, complete with the rock layers above and below for study, and found almost no presence of volcanic sediments.
The presence of land mammal fossils was also an unlikely cause of the algal bloom known as red tide.
"These animals were dying over the whole area, but no sediment deposition was going on, possibly related to rising sea levels that snuffed out silt and sand deposition or restricted it to the very near-shore environment," Pyenson said.
"Once the sea level started going down, then more sediment began to erode from near shore," he said.
Copyright 2009 XINHUA NEWS AGENCY
Source Citation
"Researchers claim Sharktooth Hill bone bed mystery solved." Xinhua News Agency 9 June 2009. InfoTrac Diversity Studies eCollection. Web. 31 Dec. 2009.
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