Live Woolly Mammoths?

Researchers have shown in the most recent issue of the Proceedings of the National Academy of Sciences that sperm from a mouse frozen for 15 years at -20 degrees Centigrade could be microinseminated to produce normal offspring. This is much longer than ever thought possible. The authors' final sentence:

If spermatozoa of extinct mammalian species (e.g., woolly mammoth) can be retrieved from animal bodies that were kept frozen for millions of years in permanent frost, live animals might be restored by injecting them into oocytes from females of closely related species.