Scientists reviewing video from camera traps watched dumbfounded as a 16-pound badger worked four days to bury a 50-pound calf carcass. Badgers, carnivores native to the American West, are generally nocturnal and spend most of their time in burrows. They are known to cache food to eat later — squirrels and rabbits, typically. No one has ever seen a badger put away such a large hunk of meat....

At the top, two flesh-toned siphons swish water over massive gills. At the bottom, a slimy, eyeless head resembles a mix of wet lips and diseased tonsils. In between, a glistening gunpowder blue body stretches up to four feet long. Instead of eating, bacteria in the creature’s gills helps it suck energy from sulfur. The whole thing is sheathed in a tusklike tube created from its secretions of...