WASHINGTON - Evolutionary relationships among the world's 10,000 bird species have been tough to decipher, but scientists on Wednesday unveiled the most comprehensive account of the avian family tree ever formulated, detailing how modern bird groups are connected based on genome-wide data from 198 living bird species.
They focused in particular on understanding the group called Neoaves, encompassing more than 90 percent of all birds, the exceptions being large flightless birds like ostriches and a group including ducks and chickens.
They found Neoaves comprised five distinct subgroups, and they were surprised to learn that one of these, the water birds, spanned all diving, wading and shorebirds like pelicans, albatrosses, gulls, flamingos and storks, although not the duck lineage.
"It means that all of these aquatic birds may have evolved from a single common ancestor, as opposed to evolving an aquatic ecology multiple times independently," Cornell University ornithologist Jacob Berv said.
The new data confirmed hummingbirds and swifts, birds that rely heavily on vision, arose from nocturnal ancestors.
"This raises questions about how they see so well," Yale University ornithologist Richard Prum said. "Was color vision maintained in all those nocturnal birds for more than 10 million years?"
The research also confirmed most land birds evolved from a predatory ancestor.
"So the common ancestor of the woodpecker and the chickadee in your garden was a vicious, hawklike meat-eater," Prum said.
Birds evolved from small, feathered dinosaurs. The earliest was crow-sized Archaeopteryx from 150 million years ago. Yale avian paleontologist Daniel Field said the research indicated the most recent common ancestor of all modern birds probably lived about 75 million years ago.
Birds were the only branch of the dinosaur family tree to survive the mass extinction 66 million years ago following an asteroid impact. Modern birds evolved from the three surviving bird lineages.
"Living birds have a very long and complex history. Any attempt to understand their biology at a broad scale requires an understanding of this deep historical context," Berv said. "It's critical to every area of bird biology. How they act, where they live, what they look like, how they communicate — it's all linked to how they evolved in relation to each other."
The research appears in the journal Nature.