Paleontologists Sifting Through Time for Tiny Fossils : Science: Dirt and rock excavated from a freeway construction project in San Diego County may yield valuable clues about evolution.
It’s not a needle in a haystack. It’s worse. Much worse.
After digging up more than 25 tons of seemingly worthless dirt and rock, an army of paid and volunteer paleontologists face the daunting task of sifting through the sediment to find fossils as small as dust particles.
Paleontologists in April began digging through a three-foot swath of an Oceanside hillside bordering California 78. They are now facing the much harder task of making sense of what may be one of the richest deposits of fossils in the country.
While relatively large fossils found at the site, including sets of animal teeth and full skeletons, have been given much publicity, San Diego Natural History Museum workers say the real importance in the find could come from teeth belonging to rodents that could fit in the palm of a hand.
“There will be things from this site for people to work on for years to come,” said Dan McGuire, a paleontologist with the museum.
Museum scientists say they may have found as many as two dozen new species of now-extinct animals that had lived in the Eocene epoch about 45 million years ago, including a primate that stands about knee-high and an ancestor of pigs and goats.
“It’s really going to shed a lot of light on what life was like in the late Eocene epoch,” said Matt Colbert, 28, who is working on his master’s thesis in paleontology at San Diego State University and has been employed by the museum to develop an exhibit on fossils in the county.
Scientists from outside the area who have studied the Oceanside dig say it may tell a lot about fossil finds in other parts of the country as well as in San Diego County.
“The fact that they’ve got parts of pieces of jaws and some skulls and limb bones, we can get a much better idea of what these animals were like. . . . We’ve got more material now than we ever had before,” said Tab Rasmussen, assistant professor of anthropology at UCLA.
The Oceanside fossils are more complete and more numerous than just about any other find of fossils in the country for their time period, Rasmussen said.
So far, scientists have been trying to piece together the Eocene puzzle with just teeth and scattered bones of animals, Rasmussen said.
“It would be like a biologist going around into a tropical area saying, ‘I’m going to study these animals, but I’m only going to study their teeth and jaws.’ This site allows us to get a more complete picture of the animals,” Rasmussen said.
Teeth are particularly telltale indicators, since cuts and grooves in teeth are unique to each species. More often than not, however, scientists find a tooth from one part of the mouth and a tooth from another part and not know if they belong to the same mouth.
The complete sets of teeth that have been found in Oceanside may answer questions about fossils found in other parts of the country, Colbert said.
Museum-goers can watch as paleontologists pick carefully at what were the jaws and bones of an early mammal but now are embedded in rock.
But in a back lot of San Diego State sit three piles of sedimentary rock that may hold the keys to the past. The 50,000 pounds of rock and dirt must be broken and sifted, and should eventually yield about a ton of fossils and sediment.
Paleontologists will then take particles, now the size of sand granules, and inspect them under microscopes, removing fossils the size of specks of dust. The fossils will then be placed on pinheads, put in inch-high glass tubes and labeled.
“Telling a tooth from a rock is easy because it has enamel, and the enamel just jumps out at you,” Colbert said, pointing to a tooth half the size of the pinhead upon which it sat.
Paul Majors, a San Diego State student working on the fossil find, said small fossils, while less glamorous than larger fossils, tend to tell more about a time period.
“When you say ‘fossil,’ most people think of dinosaurs and those big, lunking things. They don’t thing of things that you can hold in the palm of your hand,” Majors said.
“Small rodents usually evolve faster and so are more useful in dating. They are also more sensitive to environmental change and they tend to live in one area rather than move around a lot,” Majors said.
The paleontologists had been digging at “Jeff’s Discovery Site,” named after the 12-year-old who found the first fossils there 10 years ago while Caltrans was widening the freeway.
Although the scientists were originally given just two weeks to haul away all they could, highway construction delays bought them precious time. But museum people said they may have had their last day at the site. McGuire said a large deposit of fossils will remain embedded in the hillside indefinitely, with the area fenced off from souvenir hunters.
While many fossils are crushed or lost forever during construction, paleontologists say that if it were not for the heavy machinery used for digging and grading, many fossils that have been unearthed might have gone undiscovered.
“Without a doubt, it’s a double-edged sword,” Colbert said. “We would never have found some fossils without the construction crews.”
Colbert said that most cities in San Diego County require that a paleontologist be present during the grading of a site that has potential for holding fossils.
McGuire said many developers are sensitive to the possibility of fossil finds and have become aware of their importance, often lending both machinery and time to excavation efforts.
“When you look at the fossils of animals, you see the evolution of how modern animals came into being,” McGuire said. Without them, “it’s like taking a book and tearing out all but the last two pages and saying, ‘Who cares about the first 750 pages?’ The book doesn’t make a whole lot of sense.”
“We’re still missing pieces here and there,” McGuire said, “and as we do more work, we’re finding new pages.”
