A huge desert created by global warming likely prevented early dinosaurs from migrating out of South America for millions of years, suggests an analysis of ancient rocks. (Related: "Oldest Dinosaur Found?")

At that time, during the Triassic period, the world's continents were bound together in a supercontinent called Pangaea, home to the first dinosaurs. But as dinosaurs spread, they didn't become evenly distributed across this landmass, suggests a team led by Columbia University geophysicist Dennis Kent. (Related "Supercontinent Pangaea Pushed Into Place.")

In a Proceedings of the National Academy of Sciences report Kent and colleagues note that there's an extraordinarily long time between when dinosaur fossils begin showing up in rocks in what is now South America, dated