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Bear fossils at caves might be oldest Bones may be 50,000 years old; exam comes during closure The coming closure of the caverns at Oregon Caves National Monument will give scientists a chance to test what could be the oldest bear fossils found in North America. The closure begins Tuesday and runs through March 1 for installation of a new staircase for visitors. The old iron stairs have rusted, staining the pale stone of the caves. But as the heavy hauling slows and the snow falls, a team of experts will venture into the caves and use the latest technology to test the Ice Age remains. The exact date of the visit isn't yet known, said Roger Brandt, chief of interpretation at the monument, but excitement is building for what the scientists might find. "It's possibly the oldest grizzly bear found on the continent," Brandt said. "We think it's over 50,000 years old. The oldest till now is about 10,000 years old. "We'll be able to tell within a couple of hundred years either way." If confirmed, the finding means such mammals were here "40,000 years before when we believed bears would have migrated to this region," Brandt said. The fossils, from the grizzly's back, were found last year by a team mapping the far reaches of the cave. The workers also found tracks from Ice Age-era bear and cougar near what used to be another cave entrance. Such openings formed and then closed two or three times, Brandt said, over the long history of the caves. The entrances could have stayed open for 2,000 to 3,000 years at a time, before the moving stone closed them. "That gives us a very constrained block of time, or a window, into what happened then," Brandt said. "That's what's really captivating about this whole thing." Other significant fossil finds at the cave include those of an enormous jaguar, found in 1995. The remains of the 450- to 500-pound animal were believed to be more than 20,000 years old, and one expert on the cats said the jaguar remains could also be the best found in North America. The areas where the latest fossils have been found are now nearly inaccessible to humans, Brandt said. The visiting scientists will crawl into the space and test the bear's age using thermoluminescent dating, a procedure that measures energy trapped within the crystals in the cave sediment. The process is still evolving but very effective in dating things like pottery and sand, Brandt said. It can tell scientists when Chinese ceramics were made, for example, or when a tsunami deposited sediment on land. Carbon-14 dating, which measures the amount of carbon remaining in an object, didn't work on the bear because there was no carbon left, Brandt said. Carbon takes about 50,000 years to break down, leading to the conclusion about the fossil's age. The new process is painstaking. Exposure to sunlight would destroy the evidence being measured, and the temperature of the sample taken must be kept constant, Brandt said. "It's very precise," he said. Other scientists from Arizona State University paid a visit in early summer, looking for something much smaller: tiny fossils of salamanders and frogs that may have crept in through the openings used by the bear and cougar. They took samples and their study is continuing. "The environment is ideal back there to preserve those tiny, tiny bones," Brandt said. Mail Tribune Copyright � The Mail Tribune 1998, Medford, Oregon USA