You may laugh when you first look at the Terror Bird, but these monsters were ten feet tall and weighed over 300 pounds as they made their way into North America to terrorize those who lived here. But this happened five million years ago, so there's no need to fret. They were pretty awful to the tasty prey of the time, though.
This could very well be a monster movie, but it's one episode of the PBS Digital Studios series called PBS Eons that looks at many different animals -and even plants- that no longer exist. -via Mental Floss