Feb. 7, 2008 -- Modern birds likely first emerged around 100 million years ago, well before dinosaurs became extinct, according to a new genetic study that indicates birds have been around for a lot longer than previously thought.
The prevailing theory has been that modern birds originated approximately 66 million years ago, a date that coincides with both the demise of the dinos and the age of the world's oldest known avian fossil, a duck from Antarctica.
Now the stage is set for a battle between "rock" and "clock" supporters -- paleontologists who rely upon fossils and molecular biologists who study genetic data.
Joseph Brown, co-author of the new study, relies on genetic data. He and colleague David Mindell, both University of Michigan researchers, suggest the true origin of any species happens when genetic lineages split, which may not immediately show up in physical characteristics, and therefore in the fossils.
For example, Brown told Discovery News that using genetic data, molecular biologists can say that fowl, like chickens, and waterfowl, such as ducks, split approximately 90 million years ago.
"However, did ducks and chickens, as we know them, arise at this time?" Brown asked. "The answer is very likely 'no.'"
"For some period of time following genetic splitting, the 'proto-chickens' and 'proto-ducks' were likely extremely similar in morphology and ecology," he added.
Such gene splits formed the basis of the new study, which was recently published in the journal BMC Biology. The researchers note that while genetic mutations occur at random, over long stretches of time they "tick" at a fairly constant rates.
In the past, however, calculating these rates proved challenging, since different bird lineages can tick at different rates, so applying a single rate to the entire bird family tree resulted in varying figures.
New findings on DNA synthesis, enzyme repair, links between bird species and better methods for weeding out error enabled Brown and his team to conduct one of the most detailed investigations ever into the matter.
While the goal was to reconcile the gap between the rock and clock data, Brown instead came up with the 100 million years ago origination date for birds, which other geneticists had speculated about before.
"Through consideration of these diverse dating methods and focusing on clades [groups] of birds where relationships are known well, we find corroboration for the Cretaceous origin of most lineages of birds," he said.
Brown still supports the "rock record" evidence that birds likely descended from two-footed, carnivorous dinosaurs. The ability to fly, in part, may have saved them from extinction when dinosaurs bit the dust.
"The warm-bloodedness of birds, accompanied with their ability to disperse and fly from difficult areas may have been partly responsible for their survival," he explained.
Marcel van Tuinen, assistant professor of biology and marine biology at the University of North Carolina at Wilmington, is both a rock and clock expert for bird origins. Van Tuinen told Discovery News that he agrees "with the general timescale" that's been proposed.
"My own work continues to show similar ages for the origin and ordinal diversification of modern birds," van Tuinen explained.
He added that, in addition to shedding light on the earliest avians, the genetic data also supports "a tightening of the fossil gap" in the more recent history of modern birds, since ancient bird bones may not always reveal the full picture of the bird family tree.
Related Links:
Jennifer Viegas' blog: Born Animal
Wikipedia: Antarctica bird fossil