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The history of our planet, its geography and climate were determined by the evolution of birds, as well as their diversity. DNA evidence is now enabling scientists to take a closer look at the changes, according to scienceworldreport.

"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."

Scientists selected DNA sequences for modern bird families with data from 130 fossil birds in order to create an "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."

Following the K-Pg extinction, two routes were used by the birds to cover the globe. The first followed a Paleogene Central American land bridge to North America, then moving to the Old World. The second route followed a path to Australia and New Zealand over Antarctica, which at that time had higher temperatures.

"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.