Annual excavations are underway at the Rancho La Brea tar pits in Los Angeles where paleontologists are unearthing the remains of saber-tooth cats and camels, and other early inhabitants of the region.
It is one of the world's most productive sites for paleontologists, who study the remains of ancient animals and plants. The animals being uncovered include now-extinct creatures like saber-tooth cats, giant ground-sloths, camels and other fauna long-gone from North America. There are 100 tar pits scattered through the nine-hectare site, and some have yielded giant woolly mammoths and mastodons.
The Rancho La Brea tar pits, near busy Wilshire Boulevard, was a death trap for the animals that stumbled into the asphalt. But the tar preserved their bones, and the site is a treasure trove for those who study the Pleistocene era, which ended 10,000 years ago.
Millions of bones have been found at the site, including several hundred thousand in Tar Pit 91. Excavations are underway at the pit for two months every summer. Gary Takeuchi, a curatorial assistant at the George C. Page Museum, says animals large and small are being found in the oil and asphalt. "The reason we have a concentration is the unusual situation that we have asphalt that comes up and animals got stuck or trapped, and that's why we have these large accumulations of bones here," he says.
There are no dinosaur bones at the site. Dinosaurs roamed North America millions of years before these tar pits bubbled up 40,000 years ago. But the finds at the site are nonetheless intriguing.
Tar pit 91 is a square hole measuring eight meters by eight meters. It has been dug to a depth of four meters, a level containing remains from 28,000 years ago. John Harris, chief curator at the George C. Page Museum, says two months of excavation are followed by months of analysis. "After the two months' excavation, the big fossils are taken across to the lab and are cleaned," he says. "And during the course of the excavation, we usually get about a thousand fossils, but about 50 to 75 buckets of "matrix," the dirt that was around the fossils. And we process that for microfossils, because it's the little fossils that tell us more about the climate."
The scientist says the climate was wetter and cooler here 28,000 years ago. Mr. Harris says scientists learned that the climate shifted from small fossils of insects and rodents, and of plant life. "We know that because the land-snails that we find from Pit 91 are today found only above 5,000 feet [1500 meters] in the mountains here in California. So that means it was cooler," he says. "And we also find fossil redwood trees, or the remains of fossil redwood trees in Pit 91, and,as you know, the coastal redwoods don't come this far south anymore."
A sudden climate change some 11,000 years ago helped lead to the extinction of many North American mammals. A rapid rise in temperature, which coincided and the arrival of humans on the continent, put an end to the camels and saber-tooth cats and other exotic creatures that once lived here.
Paleontologist John Harris says this is the world's leading site for recovering ancient animals trapped in tar pits. "There are a number of different asphalt sites in the world. There are three others in California. There's one in South America. There are some in Iran. In fact, you find those anywhere that you find an oil field below the land surface," he says. "But there's nothing quite like this because as far as I know, this is the richest site of its kind and also, of course, it's the only fossil site that you find in the middle of a major city."
The job of unearthing ancient creatures is exciting to workers like Lauren Michaelson, the senior excavator at Tar Pit 91. As she crouched in the pit four meters beneath the surface, she scraped the tar and earth with a trowel and said the work is tedious, but exciting. "You never know what you're going to find," she says. "It's kind of like an adventure every day. It's something new, and you're constantly learning. So it's a very good experience."
Summertime visitors to the Rancho La Brea Tar Pits can watch the excavation of Tar Pit 91, then visit the George C. Page Museum to see the remains of animals unearthed from the end of the last Ice Age. The scientists say those animals lived in a very different world from that of modern Los Angeles, but through an accident of history, their world has been preserved for modern viewers.