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Modern birds radiated before dinosaur extinction?

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great blue herons/Sunny S, Fotolia

One would think so, but this from :

“With very few exceptions, fossils of modern birds have been found only after the Cretaceous-Paleogene (K-Pg) extinction,” said Claramunt. “This has led some researchers to suggest that modern birds didn’t start to diversify until after this event, when major competitors were gone. But our new work, which agrees with previous DNA-based studies, suggests that birds began to radiate before this massive extinction.”

Perhaps that proved a hedge against extinction?

After the K-Pg extinction, birds used two routes to cover the globe: first, to North America across a Paleogene Central American land bridge and then to the Old World; and second, to Australia and New Zealand across Antarctica, which was relatively warm at that time.

Claramunt and Cracraft also found that bird diversification rates increased during periods of global cooling.

“When the Earth cools and dries, fragmentation of tropical forests results in bird populations being isolated,” Cracraft said. “Many times, these small populations will end up going extinct, but fragmentation also provides the opportunity for speciation to occur and for biotas to expand when environments get warm again. More.

See also: Convergent evolution: Distantly related birds, same crests

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Here’s the abstract:

Determining the timing of diversification of modern birds has been difficult. We combined DNA sequences of clock-like genes for most avian families with 130 fossil birds to generate a new time tree for Neornithes and investigated their biogeographic and diversification dynamics. We found that the most recent common ancestor of modern birds inhabited South America around 95 million years ago, but it was not until the Cretaceous-Paleogene transition (66 million years ago) that Neornithes began to diversify rapidly around the world. Birds used two main dispersion routes: reaching the Old World through North America, and reaching Australia and Zealandia through Antarctica. Net diversification rates increased during periods of global cooling, suggesting that fragmentation of tropical biomes stimulated speciation. Thus, we found pervasive evidence that avian evolution has been influenced by plate tectonics and environmental change, two basic features of Earth’s dynamics. (public access) – S. Claramunt, J. Cracraft. A new time tree reveals Earth historys imprint on the evolution of modern birds. Science Advances, 2015; 1 (11): e1501005 DOI: 10.1126/sciadv.1501005

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