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Possible mammoth tusk found on Santa Cruz Island

The discovery of what appears to be a full mammoth tusk on Santa Cruz Island has excited scientists and may offer a glimpse of California beach life during prehistoric times.

Scientists believe 14-foot-tall mammoths swam out to the Channel Islands from the mainland nearly 20,000 years ago, possibly lured by the sweet smell of island grassland for grazing. Later stranded by rising sea levels, the animals shrank over time to a dwarf version.

If the find is confirmed, researchers hope it will yield further clues about the evolution and eventual extinction of the pony-sized pygmy mammoths.

Scientists have unearthed mammoth remains at dozens of sites on San Miguel and Santa Rosa islands. But such finds are much rarer on Santa Cruz, where the animals would have struggled to negotiate the steep peaks and find sufficient grass to feed on amid the rugged terrain.

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“This is the most substantial and significant find of mammoth remains on Santa Cruz Island,” said Lotus Vermeer, who heads the Nature Conservancy’s Santa Cruz Island project. “These kinds of finds are exciting because they add pieces to the puzzle, which helps to enlighten us on our past.”

Kristina Gill, an archaeology graduate student at UC Santa Barbara, stumbled across the 4-foot-long tusk earlier this month while working on the island’s mountainous northern shore. Nearby, she found several bones that could also have come from a mammoth, Vermeer said.

But another researcher consulted by the Nature Conservancy said that the remains looked more like those of a marine mammal and that it would take an excavation to settle the matter.

At 96 square miles, Santa Cruz is the largest of the eight Channel Islands off the coast of Southern California. Scientists believe Santa Cruz, San Miguel and Santa Rosa were once joined with Anacapa to form one large northern island they call Santarosae.

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They postulate that mainland Columbian mammoths, ancestors of the modern elephant that stood nearly 14 feet tall, swam across the Santa Barbara Channel during the Pleistocene Epoch, when sea levels were lower and Santarosae was only a few miles away.

Centuries later, the theory goes, the sea began to rise to contemporary levels, isolating the animals from the mainland. As competition for food increased on the islands, smaller and more nimble animals were better adapted to survive, and the species began to shrink in size. Researchers have found remains of both the Columbian and pygmy species on the islands.

So far, the most significant remains found on Santa Cruz, including a tusk unearthed in 1985 and a portion of a femur and a humerus found in 2005, have belonged to the Columbian variety. But Vermeer said the latest find was small enough that it could have belonged to a pygmy mammoth.

It is the first time that scientists believe they have found mammoth remains in the steeper northern portion of the island. Previous finds have been in the southwestern section, Vermeer said. “It’s very, very intriguing,” she said.

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If the finding is confirmed, scientists will want to determine the age of the remains using radiocarbon dating. Previous finds suggest that humans may have arrived while mammoths still roamed the islands, raising the possibility that the animals were wiped out through hunting. The earliest human remains found on the islands date back about 13,000 years, while the most recent mammoth skeleton dates from about 12,800 years ago, Vermeer said.

Global warming during prehistoric times may also have contributed to the mammals’ demise, researchers say.

Gill was researching the prehistoric use of plant remains at a field center hosted by the Nature Conservancy when she made the discovery in a canyon. She said she was trying to figure out how Chumash Native Americans had accessed the sea from a site high above when her attention was drawn to an unusual deposit of sandstone amid the volcanic rock.

“I was looking up at the geology,” she said. “I looked down to take a step, and I almost stepped on the tusk.”

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Looking around her, she saw several other bones embedded in the sandstone and began taking pictures.

“I was alone, so I was laughing out loud to myself,” she said. “It’s not really my research area, but it’s exciting.”

Gill showed the pictures to the country’s leading mammoth expert, Larry Agenbroad, director of the Mammoth Site of Hot Springs in South Dakota. Agenbroad told the Nature Conservancy that the partially embedded remains appeared to include a mammoth tusk, several ribs and possibly a femur, Vermeer said. Agenbroad was not available for comment Wednesday.

Another researcher, who reviewed three of the photographs, disputed that analysis. Paul Collins, curator of vertebrate zoology at the Santa Barbara Museum of Natural History, said what looks like a tusk has features that are more consistent with a fossilized jawbone from an extinct species of whale. He added that the type of solidified sandstone in which the remains were found often contains marine remains.

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The Nature Conservancy has invited Agenbroad to take charge of an excavation starting next week. Agenbroad also led the recovery of the most complete skeleton of a pygmy mammoth uncovered on Santa Rosa in 1994.

After the remains have been studied, they will be turned over to the Santa Barbara Museum of Natural History, which has also been invited to participate in the excavation, along with the National Parks Service, Vermeer said.

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alexandra.zavis@latimes.com

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