Neoaves is the enormous living bird branch that includes nearly all the birds most people see in everyday life. Crows, blackbirds, sparrows, robins, hawks, owls, hummingbirds, parrots, pigeons, woodpeckers, penguins, and flamingos all belong here. In simple terms, if a bird is not part of the ostrich-tinamou branch (Palaeognathae) and not part of the duck-chicken branch (Galloanserae), it is probably part of Neoaves, which contains the overwhelming majority of living bird diversity.

The genetic clock has often suggested that the deepest roots of Neoaves may reach back into the Late Cretaceous, which is why a representative date like ~78 million years ago (±4 million) can work as a DNA-leaning timeline choice. That kind of date does not mean modern crows, sparrows, or hummingbirds already existed then. It means the ancestral line leading toward the great “everything else” branch of living birds may already have been separating from other neognaths before the asteroid impact, even if the familiar modern groups came later. Some genomic studies have favored a Neoaves radiation beginning around the K–Pg boundary, while others have allowed a somewhat deeper Cretaceous root for the branch.

The fossil record is what keeps the debate alive. The K–Pg extinction event happened about 66 million years ago, and the strongest recent genomic work says the early divergences in Neoaves were tightly associated with that boundary, with only two divergences falling before it and all later divergences after it. Early fossils such as Tsidiiyazhi abini, dated to about 62.2–62.5 million years ago, show that major neoavian lineages were already diversifying rapidly in the earliest Paleocene. So the debate continues in familiar fashion: the clocks may hint at a somewhat older Late Cretaceous origin for the branch, while the rocks show the clearest burst of recognizable neoavian diversity just after the extinction event.