How do emperor penguins survive underwater long after their oxygen should be depleted?

Emperor penguins are the undisputed champions of diving in the world of birds. They can travel more than 500 meters below the surface, and stay submerged for more than 20 minutes, even though by all accounts their oxygen should run out in just a fraction of that. So how do they pull off this incredibly cool trick? » 5/12/11 4:04pm 5/12/11 4:04pm