This images provides a montage of the skulls of several reptiles known as crurotarsans -- cousins of today's crocodiles -- that were the main competitors of dinosaurs from 230 to 200 million years ago during the late Triassic period. Thanks to a big stroke of luck 200 million years ago, dinosaurs beat out a fearsome group of creatures competing for the right to rule the Earth, scientists said on September 11, 2008. (Stephen Brusatte/Columbia University/Handout/Reuters)