I was curious about this one myself a couple months ago. The last common ancestor of all birds lived early enough that it's descendants had enough time to evolve into the four main families of birds by the time the mass extinction event that killed the dinosaurs happened. So it was multiple species of birds surviving that eventually became the birds we have today.
MayorOfBubbleTown t1_iybbag5 wrote
Reply to Which species of dinosaurs had feathers, and how much do we know about them? by chaosperfect
I was curious about this one myself a couple months ago. The last common ancestor of all birds lived early enough that it's descendants had enough time to evolve into the four main families of birds by the time the mass extinction event that killed the dinosaurs happened. So it was multiple species of birds surviving that eventually became the birds we have today.