By Sara Novak

You can't protect an animal that you don't know exists. Tapanuli orangutans, for example, are found only in the Tapanuli region of Sumatra; they were only identified as a species last year, when scientists found them to be genetically different from other Bornean and Sumatran orangutans. With just 800 left, this newly discovered species is the most critically endangered ape.

It's hard to believe that with only seven great ape species on the planet—Tapanuli, Sumatran and Bornean orangutans, eastern and western gorillas, chimpanzees and bonobos—a species could have gone undiscovered until 2017. But, in fact, new research shows that many mammals still fly under the radar.