According to some estimates, a species is lost every 20 minutes. This shocking number considers factors like habitat loss but also includes approximations of the planet's total number of species, known and unknown.
Actually declaring a species extinct, however, is a long and laborious process that requires evidence beyond a reasonable doubt the plant or animal has disappeared from the face of the earth. The difficulty of this process is highlighted by the fact that only 875 extinctions have been officially documented since 1500.
And a few of those 875 have made miraculous reappearances.
Sierra Nevada Red Fox
One such species was the Sierra Nevada red fox. It was thought extinct until U.S. Forest Service biologists captured photos of the fox with a camera trap in 2010. Researchers also took DNA samples of saliva pulled from a bait bag the fox bit into to experts at the University of California, Davis. Lab tests proved that the Sierra Nevada red fox was back.
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Photo credit: Keith Slausen/US Forest Service