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The buzz on ancient flies in Antarctica

Fossils could rewrite history of ice continent

By Marsha Walton
CNN

Scanning electronic micrograph of the Antarctic fly fossil, top. The pupa is slightly crushed with silt grains embedded it. Another micrograph image, bottom, shows a modern cousin, a blowfly puparium, from a similar vantage point.
Scanning electronic micrograph of the Antarctic fly fossil, top. The pupa is slightly crushed with silt grains embedded it. Another micrograph image, bottom, shows a modern cousin, a blowfly puparium, from a similar vantage point.

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(CNN) -- The tiny fossil of a fly discovered 300 miles from the South Pole could help scientists figure out what life was like millions of years ago in Antarctica.

The find by geologist Allan Ashworth, detailed in this week's journal Nature, could open a new chapter in the understanding of plant and animal life in ancient Antarctica and shed light on global changes in the the climate.

Until now, scientists did not think that the coldest continent ever harbored this type of flies, which are from the Cyclorrhapha family, so-called "higher flies" that include the common housefly, Ashworth said.

They could have existed during a warm spell several million years ago or could have been part of the animal life of the mega-continent Gondwana that later split up, according to researchers.

Ashworth, who started collecting fossils from quarries as a child in southern England, is recognized as a pioneer for his use of insect fossils to research climate changes.

"I really wanted to destroy the idea that the only thing you did with fossils was classify and collect them, " Ashworth said. "They are a lot more useful if they can impart knowledge."

Tiny specimens, giant implications

Looking for insect fossils is "painstaking stuff," said Ashworth, a geology professor at North Dakota State University in Fargo.

The pupa that Ashworth found was 5 to 7.5 millimeters long. The puparium stage for a fly is similar to the cocoon stage for a butterfly, a transition period between the larva and the adult insect. Ashworth was studying rocks he had collected in the Meyer Desert Formation on the Beardmore Glacier in Antarctica.

"Under the microscope, a lot of what's in the siltstone looks like sand, with lots of seeds, and occasionally the head or leg of a weevil," said Ashworth.

But he said he knew he was on to something when he saw an unusual circular pattern in the rock. It appeared to be the back end of a fly in the pupa stage.

For research entomologist Christian Thompson at the Smithsonian Institution's Museum of Natural History, a glimpse of the fossil Ashworth found was a sort of "Eureka" moment. Thompson co-authored the research published in this week's edition of the British journal Nature.

"I've spent 30 years looking at fly maggots," Thompson said. Along with basic research like this, Thompson's work also includes determining if shipments of agricultural products are safe to enter the United States.

He said he knew immediately that the circular pattern was a spiracle -- a mechanism that a fly pupa uses to breathe. A close look at the rest of the fossil, with small circular patterns, showed how the pupa had moved around in the soil or vegetation as it grew.

Thompson said this discovery leads to questions that go beyond the movement of these insects in the Southern Hemisphere.

"It was definitely a lot warmer than it is today, so we have to rethink the rate and ability of these flies to disperse across great land masses. We also have to think more about the climate fluctuations in the last 40 million years," Thompson said.

In the Antarctic today, with summer temperatures around 20 degrees below zero and winter temperatures that can hit 80 degrees below zero, only a couple of species of insects -- such as nonbiting mosquitoes known as "midgies" -- exist in a few areas of the continent.

So what was it like when this fly was forming some 3 million to 17 million years ago?

Professor: Antarctica once like Greenland

Researchers say when the fly inhabited this area, the Beardmore valley would have been an ice-choked fjord.
Researchers say when the fly inhabited this area, the Beardmore valley would have been an ice-choked fjord.

"The landscape at that time was sort of like what's on the west coast of Greenland now," Ashworth said. "There was a lake, ice sheets that are much smaller than they are today and some patchy, tundra-like vegetation."

Along with the fly, there were beetles, snails, algae, mollusks and some fish in the region.

The authors give two possibilities on how the flies came to inhabit the southernmost continent. Possibly they colonized Antarctica in a warm period in what was known as the Neogene epoch, between 3 million and 17 million years ago.

Or they could have been native to Gondwana, an ancient land mass that included Antarctica, as well as regions now known as South America, India, Australia, New Zealand and Africa, Thompson said. If that were the case, the fly survived in Antarctica for tens of millions of years before becoming extinct.

Ashworth said the next step in his research is to hunt for more insect fossils. He said their discovery could lead to dramatic revisions of the origin of the higher fly.

And perhaps there is more to be learned about global warming from some of these ancient clues, according to Thompson.

"We have to look at the models more closely: Obviously it wasn't greenhouse gases warming Antarctica 15 million years ago," he said. "Some other variables, other than human variables, caused [it]."


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