Oops. As it turns out, 36 percent of marine megafauna died out at the end of the Pliocene epoch. That's over a third of the mammals, sharks, turtles, and seabirds that died out as the climate changed. The analysis, published in Nature Ecology & Evolution on Monday, also found that marine mammals suffered the worst losses. They had 55 percent less biodiversity after the extinction, whereas sharks only lost 9 percent. And there wasn't just less biodiversity—there was less functional diversity, too. Those might sound like the same thing, but functional diversity has a much larger impact. Biodiversity is about a loss of species, not a loss of functional roles in an ecosystem. If one seal dies off, but another species of seal fills the same niche and can grow in number to make up for the loss, it's less of a problem. If a seal dies off and nothing else fills their ecological niche, that could spell the end. Or, at the very least, it makes the entire ecosystem more fragile, more susceptible to change.