Skulls are potent symbols of death, life and danger, and they also can tell a fascinating story about natural history. Ross Reynolds talks with writer Simon Winchester about his new book about skulls and a man that obsessively collects them.
Some 66 million years ago, about 75 percent of species on Earth disappeared. It wasn't just dinosaurs but most large mammals, fish, birds and plankton. Scientists have known this for a long time just from looking at the fossil record. If you dig deep enough, you find lots of dinosaur bones. And then a few layers up, they're gone.
But scientists couldn't figure out exactly what had caused this phenomenon. Of course, there were lots of theories.