The biggest animals ever to have walked on Earth were the long-necked, long-tailed dinosaurs known as sauropods, and the most famous of these giants was likely Brontosaurus, the "thunder lizard." For more than a century, scientists stopped using the genus name Brontosaurus, but in 2015, researchers suggested it was time to "resurrect" it. So why was Brontosaurus brought back from the dead, so to speak?