DNA congelado nos sedimentos de permafrost revela ecossistemas antigos

segunda-feira, novembro 21, 2011

DNA frozen in permafrost muck reveals ancient ecosystems

By Ed Struzik, Postmedia News November 19, 2011

University of Alberta scientist Duane Froese examines an sheet of permafrost in the Yukon that has yieldd the bones of Ice Age animals
Photograph by: Brent Aloway, Edmonton Journal

DNA frozen in permafrost muck reveals ancient ecosystem teeming with wildlife. 


Postmedia News

EDMONTON — University of Alberta scientist Duane Froese was on sabbatical last summer when he received a call from a Yukon miner who wanted to give him the heads-up about a site he planned to excavate.

Like most Klondike miners, Tony Beets is a character. He’s tall, bushy-haired, drives fast and uses colourful language.

But he’d also been incredibly helpful over the years, moving in heavy equipment for scientists such as Froese, exposing layers of ancient permafrost that yielded the frozen bones of woolly mammoths, scimitar cats, short-faced bears and other animals that lived in this part of the world before the last major Ice Age ended 11,500 years ago.

As much as Froese had vowe

As it turned out, she was right, and Froese was more than happy to admit that he had been wrong.

Shortly before he arrived on the scene, his team already had unearthed some woolly mammoth bones that Beets had exposed.

The fossil that stood out the most, however, was the skull of a horse that had lived in the Arctic during the last Ice Age.

This was not the typical small Yukon horse that Froese and other paleontologists had found here and in other regions of the Arctic. This was a huge animal — a Clydesdale next to an Icelandic pony — that probably would have had an easier time outrunning scimitar cats, American lions and short-faced bears that prowled this ancient world around the same time.

“The fossils of horses like these show up rarely in North America,” says Froese, who considers himself to be a geologist rather than a paleontologist.

“To have some that are incredibly preserved in permafrost, and the chance to directly date them, is really significant. It was exciting to see more of these horses at a site where we could get a potentially rich record of the environment they were part of.”

This isn’t the first time that scientists had found evidence of a “Lost World” in the western Arctic.

Most people, however, barely noticed when Canadian Museum of Nature paleontologist Dick Harington found the bones of woolly mammoths, scimitar cats, eight-foot-tall beavers and other Ice Age animals in the Yukon while working on his PhD at the University of Alberta in the late 1960s and early 1970s.

Harington’s findings, and those of others who followed, painted a remarkable picture of a vast steppe land that was free of ice because the climate was too dry to allow for the formation of glaciers that covered most of continent.

In a world where a large percentage of the Earth’s water was locked up in those massive glaciers, ocean levels were so low that countless Siberian animals were able to cross over to Alaska and the Yukon by way of the Bering Land Bridge that connected the two continents.

No one knows exactly why half of these Ice Age animals disappeared from the landscape so quickly. Most scientists attribute it to a rapidly warming climate that resulted in succulent grasses being replaced by woody shrubs and trees.

Others believe that disease, or an extraterrestrial impact may have been responsible. A few even have suggested the humans who eventually followed these animals into Alaska and the Yukon hunted them to extinction.

Working with geneticist Eske Willerslev, Yukon paleontologist Grant Zazula and other scientists from Australia, Scotland, England, and the United States, Froese found evidence at a site along the Yukon River in Alaska a few years ago that puts a new, radical spin on the debate.

The evidence they found near Stevens Village showed that some Ice Age animals such as the woolly mammoth and the giant horse lived several thousand years longer than previously thought in so-called “ghost ranges” of the western Arctic.

“Surprising as it might seem, it was not a shock when you consider the fact that large mammals like mammoths and horses survived through previous periods of rapid warming such as that which occurred at the end of the Pleistocene (Ice Age),” Froese says. “They must have found a refuge somewhere. So, there’s no reason why they couldn’t find one again.”

What is surprising is how Froese and his colleagues came to this conclusion. The evidence they unearthed from that site along the Yukon River in Alaska didn’t come from fossils; it came from the DNA extracted from the hair, skin, feces, urine or possibly skin cells that the animals left behind. Frozen in permafrost, and uncontaminated by other genetic material that may have been deposited later on, this DNA was well enough preserved for scientists to be able to identify the animal from which it came.


Read more here/Leia mais aqui: Edmonton Journal