Bill Bryson said this quote

“ Three hundred types of mussel, a third of the world’s total, live in the Smokies. Smokies mussels have terrific names, like purple wartyback, shiny pigtoe, and monkeyface pearlymussel. Unfortunately, that is where all interest in them ends. Because they are so little regarded, even by naturalists, mussels have vanished at an exceptional rate. Nearly half of all Smokies mussels species are endangered; twelve are thought to be extinct.This ought to be a little surprising in a national park. I mean it’s not as if mussels are flinging themselves under the wheels of passing cars. Still, the Smokies seem to be in the process of losing most of their mussels. The National Park Service actually has something of a tradition of making things extinct. Bryce Canyon National Park is perhaps the most interesting-certainly the most striking-example. It was founded in 1923 and in less than half a century under the Park Service’s stewardship lost seven species of mammal-the white-tailed jackrabbit, prairie dog, pronghorn antelope, flying squirrel, beaver, red fox, and spotted skunk. Quite an achievement when you consider that these animals had survived in Bryce Canyon for tens of millions of years before the Park Service took an interest in them. Altogether, forty-two species of mammal have disappeared from America's national parks this century. ”