The Circus sandersi may be the largest flying bird ever . It had paper - thin hollow bones , but may have needed a running start to fly . But the weight of the discovery was n't publicized until this week , when scientists unveiled the findings in the journal Proceedings of the National Academy of Sciences . Scientists believe it lived 25 million to 28 million years ago . Construction workers found the bird while building an airport runway .
The Circus sandersi may be the largest flying bird ever . It had paper - thin hollow bones , but may have needed a running start to fly . Scientists believe it lived 25 million to 28 million years ago . Construction workers found the bird while building an airport runway .