Scientists have held out hope of resurrecting the woolly mammoth by extracting sperm from animals encased in ice.
Researchers made the discovery sperm from the frozen reproductive organs of dead mice can produce offspring.
Writing in the journal Proceedings of the National Academy of Sciences, they suggest sperm from frozen mammoths could be used to bring the extinct creatures back to life.
The idea would be to inject mammoth sperm, into the eggs of female elephants.
A successful pregnancy would produce the closest thing possible to a living Woolly Mammoth, the result of crossing one of the extinct animals with a close modern day relative.
Sperm is routinely frozen for In-Vitro Fertilisation treatment, but has to be carefully stored and protected.
The new research showed that it is possible simply to freeze whole male mice, or their reproductive organs, and use the sperm extracted from them to produce offspring. In one test, sperm were retrieved from the bodies of mice that had been kept frozen at minus 20C for 15 years.
Some of them successfully fertilised eggs after being injected into them.
It was not known how long viable sperm could be frozen in animal bodies, said the researchers. But the findings raised the intriguing prospect of resurrecting extinct animals that had remained frozen since the ice age.