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Asteroid Impact Helped Create the Birds We Know Today (sciencemag.org)
sciencehabit writes: Every bird alive today can trace its ancestry to creatures that lived about 95 million years ago on a chunk of land that split off from the supercontinent Gondwana, a new study suggests. The new family tree, compiled using information from fossils and from genetic analyses of modern birds, also reveals that this lineage underwent a major burst of evolution after an asteroid slammed into Earth about 66 million years ago and killed off the rest of their dinosaurian kin.
According to the article "future birds" populated western West Gondwana and didn't spread until the dinosaurs died out. In other words they would not have moved in 30 million years and then suddenly they spread wildly when the dinosaurs vanished. Looking at how animals spread today and in recent history, it looks like they spread unless there is something preventing them from spreading, such as oceans or mountains. There is no reason to think it was any different back then and either they could walk/fly around to spread or they couldn't. There could be plenty of reasons why no fossils is found in an area even though the animal existed in that area. One could be that they haven't been found, another could be that past events prevented them from being created/preserved. Lack of evidence of existence is not evidence of lack of existence.
If "birds" existed in a greater area in low numbers and haven't been found, then the evolution explosion could be explained by multiple already existing birds growing rapidly in numbers and suddenly started to appear in the fossil records. They "cheated" and started their evolution earlier than we can detect, means the rapid appearing new diverse species was more of a growth in numbers than in species.
Sure this is pure speculation, but I think the same goes for the version provided in the article. I never understood why it is assumed when something is found, it's the earliest or latest member of the species to have ever lived. Most likely neither would be the case, which mean the timeframe of species will have to be open ended, yet if you look up a species, you get a closed ended timeframe based on the age of found fossils. I don't think it can be any different (we have to write what we know, not what we assume), but we should always remember the disclaimer that no fossils is not proof of non existence, both in age and geographical location. If it was, then some species would die out and then suddenly revive themselves 2 million years later.