Many of the early birds suffering from the same catastrophic extinction of the dinosaurs, new research has shown.
Impact of meteorites at the same time that the disappearance of the dinosaurs 65 million years ago, also saw the rapid decline in species of primitive birds.
Few groups of birds have survived the mass extinction, from which all modern birds are descended.
Researchers at Yale University published their findings in PNAS this week.
There was a long-standing debate over the fate of the first "archaic" birds, which first evolved about 200 million years.
It's population has declined slowly to the end of Cretaceous time, or are suddenly the mass extinction at the Cretaceous-degree (KT) boundary is unresolved, because the conflicting evidence.
DNA studies have attempted to date the origin of modern birds, some suggest that arose before the extinction of the dinosaurs, many of them survive the extinction event.
But the molecular clock is suffering from "methodological problems", says Dr. Longrich Yale University, and well-dated fossils are needed to "stress stratigraphic" extinctions.
The problems are the fossil record, however. It is incomplete because of the extreme rarity of fossils of birds.
The bones of birds are very difficult to maintain as fossils because they are small and lightweight, and easily damaged or washed away into rivers.
But the new study, led by Dr. Longrich, made use of fragmentary fossils of birds gathered until 100 years ago from different parts of North America.
New diversity
The fossil beds in North and South Dakota and Wyoming in the United States and Saskatchewan in Canada, the date from 1.5 million years of the Cretaceous period.
Specifically dating places the fossils of birds within 300,000 years of extinction - a very short period of geologic time.
These fossils were studied before, but have been "shoehorned" into groups based on their similarity to modern general.
Dr. Longrich and his team re-analyzed and reclassified these important fossil fragments, with the characteristics of the shoulder joint to assign the fossils of ancient and modern groups.
The bones of the shoulder, or "coracoid" used for classification, because it is the piece of bone most commonly preserved, and it does not vary much between individuals of the same species.
24 samples analyzed, the researchers identified 17 species, seven of which were "archaic birds" which are not observed after the KT mass extinction.
These results show for the first time a variety of archaic birds live to the end of the Cretaceous.
This would mean that the birds went extinct suddenly 65 million years ago, archaic, and that modern birds are descended from only a few groups, who survived the accident.
"The nail in the coffin"
Among the species identified early, there is considerable variation in size, but there are some specific adaptations.
Birds of today, however, has a wide range of adaptations, in particular their behavior or habitat.
This change would be born in an explosive evolutionary radiation during the few surviving groups, the first 10 million years after the KT mass extinction.
"It is similar to what happened to mammals due to aging dinosaurs." Long said Dr. Rich.
"Given that mammals hit eradication, reptiles, insects and plants, it would be surprising if the bird survived the incident unharmed," the researchers say in an introduction to their research.
There is evidence of growing for the theory that birds survived to the archaic extinction of fossil birds more were found in Madagascar, Mongolia and Europe.
But these fossils are not well dated, in contrast with the recently analyzed the fragments of North America.
Dr. Rich Long said that this display is a "nail in the coffin of the concept of slow decline."
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