There was one branch of the dino family that became birds. Other branches didn’t. The bird branch was the one that survived whatever killed off the other dinos.
There were some really large aggressive land birds in the Paleocene, perhaps this line survived in enough quantity to reproduce rapidly. My theory is that after all the other bad stuff from the boloid extinction, another problem was that the ozone layer was severly damaged or gone for a while. Anything with feathers, nocturnal habits, living underground, hibernating in the mud, etc. had a better chance of surviving. Thus we have birds, mammals, snakes, frogs, turtles, alligators, etc., but adios dinosaurs.
If you’ve got an enormously long time horizon, enough branches (harshly pruned or nimbly grafted as needed) and are comfortable with flexibly interpreted morphogenesis and physiogeny, presto you can ‘evolve’ anything.
You could also simply repeat “ontogeny recapitulates phylogeny” a thousand times and then just turn your brain off.