Terror birds lived 64-2 million years ago in South America. The Isthmus of Panama marked the end of the reign of birds. They were the apexes of the era. But of corse the reign of any animal is soon dead and extinct. They were 3-12 feet tall. And there bones were hollow of corse due to the fact that they were birds. Thus due to having bones they weighed little. But where flightless.