jueves, 11 de junio de 2009
Ancient Underwater Camps, Caribou Traps in Great Lake?
Under North America's second largest lake, robot-assisted archaeologists may have discovered prehistoric American camps and long "drive lanes" built to guide caribou to their deaths, a new study says (caribou pictures and facts).
On what was once dry land, the structures likely date back 10,000 to 7,500 years. At the time, a vast land bridge divided what is now Lake Huron, researchers say (Lake Huron map).
Now mussel- and algae-encrusted, the features were uncovered by sonar and underwater robots at depths ranging from 60 to 140 feet (18 to 43 meters).
Walk This Way, Caribou
One of the structures in the lake, which straddles Michigan and Ontario, Canada, appears to be a line of carefully placed rocks that stretches longer than a football field.
The line resembles lanes still used by Arctic caribou hunters, according to the study.
"An interesting behavioral trait of caribou is that they follow linear features," said University of Michigan archaeologist John O'Shea, who co-authored the new study, which will be published tomorrow in the journal Proceedings of the National Academy of Sciences.
"The hunters recognized this, and the drive lanes were a way of casually suggesting, Why don't you walk this way?"
The drive lane may have been built by early North American settlers called Paleo-Americans—ancestors of later Native American tribes.
The stone line is relatively straight but curves inward at one point.
O'Shea thinks the curve may have been a hunting blind, where hunters waited to ambush animals as they approached.
In addition to a drive lane, the scientists think they may have spotted camp sights and stacked stones, or cairns, that prehistoric Americans used to attract the caribou's attention.
Today Arctic hunters use "cairns to lead the caribou onto the drive lines," O'Shea explained.
The hunters "will sometimes attach ribbons to [cairns], and caribou are sufficiently curious that, when they see this, they want to come up and take a look."
Huron Mystery to Be Solved This Summer?
If the new finding is confirmed, it will be the first direct proof that Paleo-Americans living in the Great Lakes region hunted caribou on large scales like their counterparts farther north, said Michael Shott, a University of Akron anthropologist who was not involved in the study.
But Shott is not yet completely convinced the structures are human-made.
"The argument is a plausible one," he said. "But there may be natural processes that could produce both the large- and small-scale features."
Study co-author O'Shea agreed that processes such as glacial scraping could have produced the rocky lines.
The mystery, he said, could be resolved this summer, when scuba divers will examine the lake bottom.