Tiny Fossils Reveal Warm Antarctic Past

Kimberly Johnson
for National Geographic News

July 25, 2008

Hundreds of fossils of crustacean-like animals no bigger than a pinhead have been found in Antarctica, scientists say.

The 14-million-year-old called ostracods were found recently in an ancient lake bed in the Dry Valleys region in the continent's interior.

The well-preserved fossils are likely the last remnants of a warmer Antarctica, before a massive and intense climate cooling millions of years ago set in, new research suggests.

(Read: "Ancient Seal Remains Reveal Warmer Antarctica, Study Says" [June 26, 2006].)

"The fossils therefore show that there has been a substantial and very intense cooling of the Antarctic climate after this time interval that is important for tracking the development of the [east] Antarctic ice sheet," study lead author Mark Williams, a geologist with the University of Leicester, said in a statement.

"[It's] a key factor in understanding the effects of global warming," Williams added.

The findings were published Wednesday in Proceedings of the Royal Society B.

Tiny Relics

Study co-authors Adam Lewis and David Marchant, along with a Boston University team, were looking for volcanic ash in 2006 when they discovered deposits in the remnants of a now-dry glacial lake.

Processing the deposits back in the lab at North Dakota State, undergraduate student Rich Thomasson first noticed the fossils, which are shaped like footballs.

"Essentially the whole soft parts of the creature were preserved," including its tiny walking legs and tail, said study co-author Allan Ashworth, a paleontology professor at North Dakota State University.

The discovery marked only the fourth time in the world that the soft anatomy of such a fossil had been preserved between the two valves that connect its body, he added.

Just how the ostracods were introduced into the lake 14 million years ago—when it likely measured about 330 feet (100 meters) by 200 feet (60 meters)—remains a mystery.

The creatures could have been relics that survived on the continent after it broke away from South America almost 30 million years ago, Ashworth said.

(See a prehistoric time line.)

Or migratory birds wading into the lake could have had the organisms tangled in their leg feathers.

The permanently frozen ground also likely helped preserve the fossils, Ashworth added.

Warmer Days

Ostracods no longer live in Antarctica today. The closest place they are found is about 620 miles (1,000 kilometers) in subantarctic islands, he said.

The research team found hundreds of the ostracod shells in various stages of their growth cycles.

"It tells you this was a healthy community," Ashworth said.

Also found at the site were mosses and pollen from tundra vegetation that lived during the same period.

"What the ostracods and mosses are telling you is that this was a time that was significantly warmer than present Antarctica," Ashworth said.

(See pictures of life on today's tundra.)

Warmer temperatures would have been essential for the ostracods' survival, with summer temperatures well above freezing for months at a time, Ashworth said.

Today, summer temperatures at the site average between -4 to 13 degrees Fahrenheit (20 to 25 degrees Celsius.

Point of No Return

The findings illuminate how minor climate changes suddenly become major when a threshold is crossed, he said.

"We think that climate change 14 million years ago caused the extinction of ostracods and other animals and plants on the Antarctic continent," he said.

Since that point of no return, conditions have not warmed enough in Antarctica to allow the reintroduction of life, Ashworth said.

(Related: "Greenland Ice Shows Rapid Climate Flips, Study Says" [June 19, 2008].)

"We believe that that [glacial-lake] system has remained basically frozen for the past 14 million years," Ashworth said.

Not everyone is convinced, however.

"No question, it is a fantastic find," Reed Scherer, a micropaleontologist at Northern Illinois University in DeKalb, said of the ostracod discovery.

Scherer, who has conducted extensive research in Antarctica, was not affiliated with this study.

But he pointed out that the preservation of the ostracods may not necessarily mean they had been in continuously frozen tundra for the past 14 million years, he said.

Some assume that because the samples have not been disturbed that the Dry Valley site has remained frozen, he said.

"There's logic to that argument, but I don't see the alternative [of further temperature fluctuations] as ruled out," Scherer said.