How Earth's History Influenced the Evolution of Birds and Their Diversity

First Posted: Dec 12, 2015 07:29 AM EST

The evolution of modern birds was greatly shaped by the history of our planet's geography and climate. Now, scientists are getting a closer look at these changes with the help of DNA evidence.

"Modern birds are the most diverse group of terrestrial vertebrates in terms of species richness and global distribution, but we still don't fully understand their large-scale evolutionary history," said Joel Cracraft, co-author of the new paper, in a news release. "It's a difficult problem to solve because we have very large gaps in the fossil record. This is the first quantitative analysis estimating where birds might have arisen, based on the best phylogenetic hypothesis that we have today."

The researchers analyzed DNA sequences for most modern bird families with information from 130 fossil birds to generate a new evolutionary time tree.

"With very few exceptions, fossils of modern birds have been found only after the Cretaceous-Paleogene (K-Pg) extinction," said Santiago Claramunt, one of the researchers. "This has led some researchers to suggest that modern birds didn't start to diversify until after the 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."

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

"When the Earth cools and dries, fragmentation of tropical forests results in bird populations being isolated," said Cracraft. "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. This work provides pervasive evidence that avian evolution has been influenced by plate tectonics and environmental change."

The findings are published in the journal Science Advances.

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