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Thursday, February 19, 2009

Major cache of Pleistocene ice age fossils unearthed in L.A. Options

February 18, 2009


Workers excavating an underground garage on the site of an old May Co.
parking structure in Los Angeles' Hancock Park got more than just a
couple hundred new parking spaces. They found the largest known cache
of fossils from the last ice age, an assemblage that has flabbergasted
paleontologists.


Researchers from the George C. Page Museum at the La Brea tar pits
have barely begun extracting the fossils from the sandy, tarry matrix
of 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, to be formally announced today, is the nearly
intact skeleton of a Columbian mammoth -- named Zed by researchers --
a prize discovery because only bits and pieces of mammoths had
previously 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. In the early 1900s, 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 also is pioneering a new
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 from the site have been
removed intact and now sit in large wooden crates on the museum's back
lot. The 23 crates -- ranging in size from that of a desk to that of a
small delivery truck -- are responsible for the excavation's informal
name, Project 23.


The site of the old two-story parking garage, which was used by the
now-defunct May Co. department store, is now owned by the Page's
neighboring museum, the Los Angeles County Museum of Art. LACMA had
razed the building to construct an underground parking garage that
would restore parkland above the structure.


The entire Rancho La Brea area at Hancock Park is a paleontological
treasure chest. Petroleum from the once-massive underground oil fields
oozed to the surface over the millennia, forming bogs that trapped and
killed unsuspecting animals and then preserved their skeletons. It is
now a protected site, although 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, which 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 LACMA 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 a process similar to that used to move large living
trees. Carefully identifying the edges of each deposit, her team dug
trenches around and underneath them, 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
individually with a heavy crane. The biggest one 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 entire collection two years ago and delivered them to the
museum. For some of the deposits, she said, they had to wear oxygen
tanks with full gas masks because of unusually 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 other
assemblages, they were partially excavated and encased in plastic
casts for cleaning in the museum -- the conventional technique for
recovering fossils.


Curators are excited about Zed because he appears to be about 80%
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. Mammoths on display at the museum are
assembled from the bones of many animals.


Zed's tusks also are nearly intact -- another rarity since they are
made of dentin, which is much more fragile than bones.


Zed's skeleton is now being cleaned in the museum's "fish bowl"
preparation room, and the team of paleontologists and volunteers has
so far 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 normally lived to about 60, so Zed died
prematurely.


Curators have found three broken ribs that were healed before his
death. He probably got them from fighting with other male mammoths,
"or he was just clumsy as hell," said Shelley M. Cox, who is
supervising the cleaning.


The team also has begun digging through the largest crate but has so
far excavated only an area about 6 feet by 4 feet and about 2 1/2 feet
deep. From that small area, they have so far removed a complete saber-
tooth cat skeleton, 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 individual plant and animal specimens,
400 of which have been cataloged, Shaw said.


The team doesn't know the ages of the deposits yet. All previous
specimens from Hancock Park 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 radiocarbon-dated.


Individual fossil deposits in the area generally cover a time span of
about 2,000 years, Harris said, and deposits that are 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.
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