You can't begrudge him some satisfaction in killing a threat to his livestock. What Batty did not know—could not know—is that he'd just made the last documented kill of a wild thylacine, anywhere, ever. In six years, the wonderfully odd striped-back creature—the largest marsupial carnivore known—would be extinct in captivity as well.

The thylacine is one of 795 extinct species on the International Union for Conservation of Nature's Red List, which since 1963 has been tracking the planet's biodiversity. The animals and plants on the list are organized into categories of increasing degrees of urgency, from "near threatened" through "critically endangered," until you reach the last "extinct" group, whereupon the urgency abruptly plummets to zero. An endangered species is