The evolution of modern birds has been greatly shaped by the history of our planet's geography and climate, revealed a new research led by the American Museum of Natural History.
The DNA-based work has found that birds arose in what is now South America around 90 million years ago, and radiated extensively around the time of the Cretaceous-Paleogene extinction event that killed off the non-avian dinosaurs.
The study said, "Birds in South America survived the extinction event and then started moving to other parts of the world via multiple land bridges while diversifying during periods of global cooling."
Cracraft and lead author Santiago Claramunt, a research associate in the museum's department of ornithology, analyzed DNA sequences for most modern bird families with information from 130 fossil birds to generate a new evolutionary time tree.
Claramunt said, "With very few exceptions, fossils of modern birds have been found only after the Cretaceous-Paleogene (K-Pg) extinction. 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."
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.
Cracraft said, "It was 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. 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 study was published in the latest issue of Science Advances.