科学家探寻冰河时代的化石

Ongoing excavations at the La Brea Tar Pits are revealing new details about life in Ice Age Los Angeles, tens of thousands of years ago. For more than a century, scientists have been uncovereing the remains of ancient animals trapped in the tar pits' thick, oily pools. They continue to make important discoveries among the treasure trove of fossils.

It can be tedious work, carefully scraping away hardened asphalt to reveal the bones of ancient mammals - dire wolves, giant ground sloths, prehistoric horses, a baby mastodon and others.

More than 200 species of vertebrate animals, many now extinct, have been found at the tar pits. A tragedy for the ancient creatures who got stuck here has been a boon to modern scientists, who find well-preserved specimens to study.

On the current excavation, called Project 23, scientists are working through 23 fossil blocks uncovered five years ago when builders began construction on a new underground garage at the Los Angeles County Art Museum, next door to the tar pits.

Chief curator John Harris oversees excavations at the Page Museum, where the tar pit findings are studied and showcased. He says some nearly complete animals have been found in the recent work.

"Normally you find lots of bone masses with bones jumbled up together. Because these deposits are smaller, we're able to identify individual animals from amongst the jumble of bones. And so we've got the baby mastodon skeleton, we've got a giant jaguar, we've got a camel, we've got several saber-tooth cat kittens," he said.

Excavators use dental picks, chisels, hammers and brushes to extract and clean the bones and other Ice Age materials, include plant remains and the occasional tree branch.

Inside the museum, a worker in a "fish-bowl" laboratory surrounded by windows works on a specimen, scrubbing and cleaning it with solvent and a toothbrush, as museum visitors gaze in.

Excavators and scientists say they are piecing together a giant jig-saw puzzle to understand what Los Angeles was like between 11,000 and 40,000 years ago.? One important discovery is a nearly complete Columbian mammoth knows as Zed. Its giant tusk sits on a work-bench. A shoulder blade rests nearby. A museum worker scrapes debris from part of the head. There are smaller animals, some more complete than others, says lab director Shelley Cox.

"Our focus in the lab is bringing them back to life and putting them in the context of what the environment was like right here, and how that animal would have functioned within that environment. What did he eat? What does that tell us about a changing environment?," Cox said.

Plant and animal remains show that this area gradually warmed after the last Ice Age. The ice didn't reach this far south, but the climate 40,000 years ago was cold in winter. It was temperate by 10,000 years ago, after humans had arrived, although it was cooler than it is today.

Through the work at the tar pits, scientists say our knowledge of Ice Age Los Angeles is growing, and excavator Laura Tewksbury says it is always exciting. "It never gets old coming into work and peeling back that little bit of asphaltic sand and finding a fossil behind it, and realizing that I'm the first human being in existence to ever see that fossil," she said.

For volunteer Herb Schiff, this a treasure hunt and each discovery is important. But one stands out for him.

"The most exciting thing I've worked on wasFluffy. And Fluffy was an animal I got to name because it took a year and a half of my life to clean him. But Fluffy is a North American lion, which you can see mounted in the museum now since I've finished working on him. And he came with an amazing number of what we call bonus bones, bones stuck to him from all kinds of other animals. So [doing] it was a tremendously wonderful job, and now that he's mounted in the museum, I get to say, 'That's my animal!,'" Schiff said.

Excavators say that thanks to the preservative powers of asphalt, scientists continue to enjoy a remarkable window into the ancient past of this Los Angeles neighborhood.