Paleontologist Paul Sereno is known for digging up dinosaur fossils. Twelve years ago, however, while tracking dinosaur remains in the Sahara desert, his team stumbled upon human bones -- a lot of them. Sereno couldn’t walk away from the discovery. He put together an international team to make sense of the 200 graves they found in the deserts of Niger. Paul's team recently returned from another expedition to the site and he discusses the findings.