The woolly flying squirrel (Eupetaurus cinereus), thought to be extinct, has been rediscovered in Northern Pakistan. The largest squirrel in the world, its rediscovery startled Dr. Charles Woods, an expert on Pakistani mammals, who noted, "We've really scoured the area and never seen it." Source: Yoon, Carol Kaesuk. 1995. "Woolly Flying Squirrel, Long thought extinct, Shows up in Pakistan," New York Times, March 14.
While it's not clear how it was rediscovered, as the Dr. Woods mentions they've never seen it, Matt Bille said that it would be examined closley in an upcoming issue of Exotic Zoology.