The evolution of modern birds was greatly shaped by changes in Earth's geography and climate, researchers from the American Museum of Natural History reveal in a new study. Over the course of our planet's history, climate change paired with tectonic activity has resulted in the extinction of some species and the diversification of new ones. Now, scientists have taken 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," Joel Cracraft, a curator in the Museum's Department of Ornithology and co-author of the paper, explained 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."
Based on the recent DNA analysis, researchers found birds arose in what is now South America 90 million years ago and diversified around the same time that the Cretaceous-Paleogene extinction event wiped out many non-avian dinosaurs. It follows then that all modern birds -- from songbirds to soaring eagles -- have evolved from a common South American ancestor that survived this event and was able to move to other parts of the world using multiple land bridges.
In the recent study, researchers analyzed DNA sequences for most modern bird families using nearly 130 fossil birds. From this they were able to create a new evolutionary tree.
"With very few exceptions, fossils of modern birds have been found only after the Cretaceous-Paleogene (K-Pg) extinction," Santiago Claramunt, lead author and a research associate in the Museum's Department of Ornithology, said. "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."
Following the K-Pg extinction, ancient birds used one of two routes to diversify across the globe. This includes the Paleogene Central American land bridge, which the birds would have used to move into North America, in addition to traveling across Antarctica to parts of Australia and New Zealand. Furthermore, researchers found bird diversification rates increase during periods of global cooling.
"When the Earth cools and dries, fragmentation of tropical forests results in bird populations being isolated," Cracraft said in the museum's release. "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."
Their study was recently published in the journal Science Advances.
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