The new deer family tree suggests that fallow deer split from giant deer between four and five million years ago, becoming smaller and sleeker over time.
Barnes says different evolutionary forces were clearly at work on the two animals, with fallow deer (Dama dama) adapting to new habitats. He says this may explain why the fallow deer coped much better than its towering relative with changes wrought by climate warming after the last Ice Age.
Previous studies suggest that the giant deer perished as dense forests replaced cool, arid grasslands and that humans possibly hunted the species.
"It probably went extinct due to environmental changes that they just weren't suited to," Barnes added.
The team identified skeletal features that are unique to both fallow and giant deer. They also found that the vertebrae of the fallow deer were once adapted to support very large antlers.
Further evidence of a close ancestral link came from mitochondrial DNA taken from both animals' bones. Mitochondrial DNA is passed down through generations from mothers to their offspring.
Barnes says DNA sequencing is shedding new light on the ancestry of many animals, providing important new insights into their evolutionary relationships.
"We're somewhat limited by the fact we can recover DNA only from relatively recently deceased organismshalf a million years at the absolute maximum," he added. "But we appear to be in the middle of a mass extinction event, so there are plenty of animals which have gone extinct in the last 100,000 years. For a number of them, there's debate over their ancestry."
Barnes says DNA data also enables scientists to gauge roughly when two species split and went their separate ways. This might hold promise in scientists' search for human origins, too.
"There's a degree of predictability about the way differences [in DNA] build up between two organisms, which is referred to as the molecular clock," Barnes said. "If you understand how the clock works reasonably well, you can get an idea of how long ago two animals shared a common ancestor."
This summer U.S. scientists announced a major breakthrough, having sequenced the genomic DNA (rather than the more easily obtained mitochondrial DNA) of two cave bears that lived in the Alps some 40,000 years agoa first for an extinct species.
Recent technological advances have raised hopes that scientists may be able to pinpoint our own closest relatives in the human family tree.
Researchers are currently trying to extract the DNA of Homo floresiensis, whose remains were found last year on the island of Flores in Indonesia.
Nicknamed "the Hobbit" because of its tiny stature, H. floresiensis is believed to have diverged from modern humans some two million years ago.
However researchers are skeptical about whether techniques that worked for extinct Ice Age animals like the giant deer will work on this diminutive species of human, which lived only some 18,000 years ago.
The problem, says Ian Barnes, is that the remains come not from Ireland or Siberia, as in the case of the giant deer, but from a tropical island.
"DNA degrades over time, and like any chemical reaction, it will degrade faster if the temperature's higher," he said. "The problem with a lot of the remains that we are asked to look at is that they've been at too high a temperature for too long a period of time.
"Our best estimate is that there won't be any DNA surviving in that [H. floresiensis] material."
James Haile, a researcher at the Ancient Biomolecules Centre at Oxford University, England, sees another complication: "Getting human DNA out of [ancient bones] is fraught with contamination problems, because every researcher who works with them is obviously human," he said.
"It's all about preservation," he added. "If the DNA's there and hasn't been degraded by heat and humidity, we could find out if we are descended from [H. floresiensis], or whether it was a dead-end branch."
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