It's now widely agreed that modern-day birds evolved, during the Mesozoic Era, from dinosaur species which survived the Cretaceous / Tertiary extinction event. (See: Avian K-T survivalplugin-autotooltip__plain plugin-autotooltip_bigAvian K-T survival
It's now widely accepted that the Cretaceous–Tertiary (K–T) extinction event (also known as the The Cretaceous–Paleogene (K–Pg) extinction event) played a large part in the extinction of the non-avian dinosaurs. (see : Dinosaur extinction )
The branch of the dinosaurs which did survive included the highly-feathered types. The )
But the question of how and why birds acquired the ability to fly is still being debated.(* see note )
There are at least five mainstream theories, some from the time of Darwin, each of which covers various aspects of the evolution, but has not yet been generally accepted as a complete explanation.
See : Wikipedia
*Note : The question of how birds manage the aerodynamics of flight goes back at least to the time of Aristotle - and has now been largely explained. But the question of the gradual development of flight only arose after Darwin's and Wallace's theories of evolution in the mid 1800s.
Also see : Feather evolutionplugin-autotooltip__plain plugin-autotooltip_bigFeather evolution
It has been known since the mid 1800s that many species of dinosaur had 'feathers'. Until the 1970s, it was widely assumed that the evolution of feathers happened concurrently as animals became able to 'glide' or fly.
In the 1970s, fossils of several species of