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The U.S. government declared the eastern cougar--a victim of bounty hunting and habit change in the 1700s and 1800s--officially extinct on Wednesday, even though the last proven sighting of the big cat occurred over seven decades ago. Why has the official declaration only come now?

Well, it's because people swear they've seen eastern cougars. According to the Pittsburgh Post-Gazette, "rumors have long existed that breeding populations of mountain lions live secret lives high in the Appalachians." In fact, there have been 108 sightings of eastern cougars between 1900 and 2010, the Christian Science Monitor explains, but no sighting since the late 1930s has been confirmed. The animals often turn out to be black panthers or western cougars, which are said to have a yellowish or gray color and a shorter tail than their eastern counterparts (eastern cougars have a yellowish-brown color). A spokesman for the Pennsylvania Game Commission tells the Post-Gazette that people who think they've seen a mountain lion have often seen "cocker spaniels, house cats or exotic pets that have escaped" instead. Cocker spaniels?

In 2007, the U.S. Fish and Wildlife Service began investigating the eastern cougar's status (it had lingered on the endangered species list since 1973) and reviewing video footage, and has now concluded that the species is extinct.

But there's another catch: the whole extinction thing might not actually be true, according to the New York Times. That's because scientists are increasingly questioning whether the eastern cougar is really any different than the western cougar, especially after a genetic study in 2000 failed to reveal significant differences. And some western cougars appear to be migrating east from states like Florida and repopulating their former habitat. What's more, extinct species occasionally come back from the dead, the Washington Post tells us. The La Palma giant lizard of the Canary Islands, for example, was classified as extinct in 2006 but reassigned to critically endangered status after several photographed sightings, earning the rarely bestowed title of "Lazarus species."

Either way, news of the eastern cougar's classification coincides with a new Nature study indicating that the world may experience its sixth mass extinction--and first since the death of the dinosaurs 65 million years ago--anywhere from 300 to 2,000-plus years from now in the absence of effective conservation measures. The researchers, who define mass extinctions as the Earth losing more than three-quarters of its species in a relatively short period, found that current extinction rates are higher than what the fossil record would suggest is normal. "This extinction trajectory would play out under conditions that resemble the ‘perfect storm' that coincided with past mass extinctions: multiple, atypical high-intensity ecological stressors, including rapid, unusual climate change and highly elevated atmospheric CO2," the researchers wrote.

In a review of the study, Time's Bryan Walsh says the good news is that "we have confirmed extinction for just a handful of species that we know of," and 190 nations agreed last year to reduce the rate of extinctions. But the bad news, he adds, is that "a warming planet headed towards 9 billion richer human beings is one that may be hostile to most species."

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