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Santa Rosa Island Yielding Bones of Pleistocene Era

{mosimage}Scientists from the Santa Barbara Museum of Natural History, UCSB and elsewhere are attempting to solve the mystery of "Arlington Man." Or "Arlington Woman."

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Kayaking along Santa Rosa Island isn’t just a step back in time as California appeared 200 years ago, it’s an exploration of life during the end of the last Ice Age, 13,000 years ago during the Pleistocene Era.

The second largest of the Channel Islands was home to "Arlington Woman" ... or is it "Arlington Man"? Whether male or female, the human remains discovered on the rugged northwest portion of the windswept island are the oldest found on the entire continent.

Back in 1959, Phil Orr, curator of both anthropology and paleontology at the Santa Barbara Museum of Natural History, discovered ancient human bones 30 feet below the surface at Arlington Canyon. The narrow canyon has one of the largest watersheds on the island, eventually snaking its way into a small, freshwater estuary that empties into the ocean.

"The cliffs are Pleistocene alluvial deposits that date back to the Ice Age," said John Johnson, the museum’s current curator of anthropology. "If you go to these cliffs today, you’ll see mammoth bones sticking out here and there."

Orr left the femur bones in place and invited scientists from around the country to verify his findings. His colleagues agreed that the bones were not the result of an erosion problem at the apex of the canyon, but deeply embedded in Pleistocene deposits.

One femur was nearly intact, while the other was fragmented and degraded. Orr believed the bones were those of a male. In the 1960s, UCSB physical anthropologist Phillip Walker took measurements of the bones and thought there was a 70 percent probability the bones were female. For several decades the femurs were known as "Arlington Springs Woman."

In September, however, visiting Utah State University physical anthropologist Patricia Lambert, who was trained by Walker at UCSB, asked Johnson, "What makes you think the bones are those of a woman?"

Lambert had studied other younger bones of males from the Channel Islands that were 8,000 years old, and they took measurements of those bones and compared them with the bones from Arlington Canyon.

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"I started pouring over Orr’s notes and found he actually recorded the diameter of the femur," said Johnson. "I contacted Phil Walker and he ran the numbers and said with all the diameters from the heads of each femur measured, there was a 70 percent probability it’s a man. It’s based on probabilities, and it’s telling us Orr was right to begin with and it should be called ‘Arlington Man.’ "

Orr had dug a huge block of earth and covered it in a plaster jacket surrounding the femurs. Scientists began studying this in 1989. Excavation of the femurs ensued to try to extract collagen for determining the age of the Arlington bones. From the same block, collagen — nature’s most abundant protein — was also extracted from an extinct species of mouse. Over a great period of time collagen can be contaminated from bacteria in the soil and from plant roots, and this was the case with the Arlington femur. Humic acid broken down from ancient flora was also examined from the same block of earth.

"One of the mouse bones had very good collagen, retaining the shape of its mandible," continued Johnson. "It was in excellent shape and gave a date of 13,400 years."

After several tests in 1999, geologist Tom Stafford used a resin filtrating technique to try to rid all the gunk out of the bones so they were just getting collagen. He came to the conclusion that "Arlington Man" lived between 13,000 and 13,400 years ago.

However, Johnson and his team of scientists wanted more proof to determine an accurate age of "Arlington Man." They excavated the sides of the canyon surrounding the site to study the geological layers, which are in pristine condition.

"One of the advantages of working on the Channel Islands is we don’t have ground squirrels or gophers churning things up all the time," he said. "Geologists consider this site in Southern California one of the best places to study changes going on at the end of the Pleistocene."

The dark soil layers date 12,000 to 12,200 years. They brought in a licensed surveyor and poured over Orr’s notes, maps and photos to try to pinpoint where the block of earth came out of the ground. After determining the location, they found more mouse bones. More photos were taken, samples of dirt were tested for radio carbon dates, and they looked to see what other critters might be present in that time period.

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Where did "Arlington Man" live? Did he have friends? Where could there be evidence of this underneath all those deposits? Did he hunt pygmy mammoths to extinction or was there another reason for their demise?

The search continues. Last summer, scientists excavated three 50-by-50-meter quadrants and used ground-penetrating radar. At a depth of 40 feet, the radar located more mammoth bones and what could theoretically be pit houses.

"It’s kind of a needle in a haystack," explained Johnson. "You’re sending down this little core sample hoping you’re going to hit something, but we have yet to analyze these cores. When we do, we’ll know about the environment at this time on Santa Rosa."

The team was penetrating two cores a day for five days. The team also found slender salamander bones, a type of bird not yet identified, and chert flakes from some sort of manufactured tool. Other cultural evidence was now turning up besides the human bones themselves.

The story of "Arlington Man" and his origins is ongoing. What scientists do know is the Channel Islands were one island, known as Santarosae, at the end of the Pleistocene, but the massive island was never connected to the mainland. In order for people to get out there, they had to have boats.

"This is an indication that way back 13,000 years ago, people were using watercraft to migrate along our coast," Johnson said.

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