By Thomas H. Maugh II | Los Angeles Times
February 22, 2009
LOS ANGELES - The largest known deposit of fossils from the last ice age has been found in what might seem to be the unlikeliest of places - under an old May Co. parking lot in this city's tony Miracle Mile shopping district.
Researchers from the George C. Page Museum at La Brea Tar Pits have barely begun extracting the fossils from the sandy, tarry soil, but they expect the find to double the size of the museum's collection from the period, already the largest in the world.
Among their finds, formally announced Wednesday, is the nearly intact skeleton of a Columbian mammoth - named Zed by researchers - a prize discovery because only bits and pieces of mammoths previously have been found in the tar pits.
But researchers are perhaps even more excited about finding smaller fossils of tree trunks, turtles, snails, clams, millipedes, fish, gophers and even mats of oak leaves. The first excavators at La Brea threw out similar items in their haste to find prized animal bones, and crucial information about the period was lost.
"This gives us the opportunity to get a detailed picture of what life was like 10,000 to 40,000 years ago" in the Los Angeles Basin, said John Harris, chief curator at the Page. The find will make the museum "the major library of life in the Pleistocene ice age," he said.
Because of its need for haste, the team is pioneering a technique for extracting the fossils. Most paleontologists spend days to weeks carefully sifting through the soil at the site of a dig. In this case, however, huge chunks of soil have been removed intact and now sit in large wooden crates on the back lot of the Page.
The 23 crates range in size from 5 feet by 5 feet by 5 feet to 19 feet by 12 feet by 10 feet - from the size of a desk to that of a small delivery truck - and are responsible for the excavation's informal name, Project23.
The site of the old two-story parking garage, formerly used by the defunct May Co., is adjacent to the Page. The Page's sister museum, the Los Angeles County Museum of Art, owned the building and had razed it to construct an underground parking garage that would restore parkland above the structure.
The entire Rancho La Brea area is a treasure chest for paleontologists. Petroleum from the huge underground oil fields oozed to the surface over the millenniums, forming bogs that trapped and killed unsuspecting animals and then preserved their skeletons. It is now a protected site, though dispensation was granted to build the new garage.
Because of the historic nature of the area, the work had to be overseen by a salvage archaeologist. In this case, the work fell to Robin Turner, founder of ArchaeoPaleo Resource Management Inc. of Culver City on Los Angeles' west side, who previously had overseen work on other sites at or near the tar pits. Her group hit pay dirt when the excavation got about 10 feet below the surface.
"I knew we would find fossils ... but I never expected to find so many deposits," Turner said.
"There was an absolutely remarkable quantity and quality."
There were 16 separate deposits on the site, an amount that, by her estimate, would have taken 20 years to excavate conventionally. But with Los Angeles County Museum of Art officials prodding her "to get those things out of our way" so they could build their garage, she had to find another way.
Her solution was similar to that used to move large trees. Carefully identifying the edges of each deposit, her team dug trenches around them and underneath, isolating the deposits on dirt pedestals. After wrapping heavy plastic around the deposits, workers built wooden crates similar to tree boxes and lifted them out with a heavy crane. The biggest deposit weighed 123,000 pounds.
"We designed a crate so that we could take out the entire deposit without disturbing it, so that at a later date you could do a proper excavation, as you would if it were still in the ground," she said.
In 3 1/2 months, working seven days a week, she and her colleagues removed the deposits and delivered them to the Page Museum two years ago. For some of the deposits, they had to wear oxygen tanks with full gas masks because of high levels of hydrogen sulfide escaping from the soil.
The only exceptions to the crating process were the mammoth named Zed and a horse skull. Because they were separate from the others, they were partially excavated and encased in plastic casts for cleaning at the museum - the conventional technique for recovering fossils.
Curators are excited about Zed because he appears to be about 80 percent complete, missing only one rear leg, a vertebra and the top of his skull, which was shaved off by excavation equipment.
Curators collected 34 mammoths in the initial excavations of the La Brea Tar Pits from 1906 to 1914. "But they were all disarticulated bones, jumbled together," said paleontologist Christopher A. Shaw, collections manager at the Page Museum. Mammoths on display there are assembled from bones of many animals.
Zed's tusks also are nearly intact - another rarity because they are made of dentine, which is much more fragile than teeth or bones.
Zed's skeleton is being cleaned in the museum's "fishbowl" preparation room, and the team of paleontologists and volunteers has completed only his jawbone and some vertebrae. All researchers know so far is that he stood about 10 feet tall at the hip and was 47 to 49 years old. Mammoths typically lived about 60 years.
Curators have found three broken ribs that healed before his death. He probably got them from fighting with other male mammoths, said Shelley M. Cox, who is supervising the cleaning.
The team has begun digging through the largest crate but has excavated only an area that is about 6 feet by 4 feet and 2 1/2 feet deep. From that area, they have removed a complete skeleton of a saber-tooth cat, six dire wolf skulls and bones from two other saber-tooth cats, a giant ground sloth and a North American lion. The tar has yielded more than 700 plant and animal specimens, 400 of which have been cataloged.
The team does not know the ages of the deposits yet. Previous specimens from the area date from 10,000 to 40,000 years ago, and there is no reason to suspect these will be any different, but each must be radio-carbon dated.
Individual fossil deposits in the area generally cover a span of about 2,000 years, Harris said, and deposits just a few feet apart can be separated in time by thousands to tens of thousands of years.
"Hopefully, the 16 [new] deposits will have 16 different ages," Shaw said.
http://www.latimes.com/news/science/la-sci-fossils18-2009feb18,0,7775847.story
