All birds evolved from feathered theropods — the two-legged dinosaurs like T. rex — beginning about 150 million years ago, and developed into many lineages in the Cretaceous period, between 146 and 65 million years ago. But after the cataclysm that wiped out most of the dinosaurs, only one group of birds remained: the ancestors of the birds we see today.Why did only one family survive the mass extinction? The newly-discovered fossil from one of those extinct bird groups, enantiornithines, deepens that mystery. ..." Mirarce eatoni’s breast bone or sternum, where flight muscles attach, is more deeply keeled than other...