Modern Birds Existed Before Dinosaur Die-Off

Sara Goudarzi
for National Geographic News
February 8, 2008

Modern birds originated a hundred million years ago—long before the demise of dinosaurs, according to new research.

In searching for the first ancestors of modern birds, studies have shown discrepancies between results from fossils and genetic analyses.

Fossil records suggest that modern birds originated 60 million years ago, after the end of the Cretaceous period about 65 million years ago when dinosaurs died off.

But molecular studies suggest that the genetic divergences between many lineages of birds occurred during the Cretaceous period.

Now a new study based on molecular evidence suggests that avian ancestors were flapping their wings some 40 million years earlier than thought.

(Related news: "Wing Angle May Be Key to Bird Flight Origins" [January 23, 2008].)

In the new study researchers applied a new method of research that looks at mutation rates across lineages.

"My goal for this study was to once and for all reconcile divergence estimates from these two sources of information," said lead study author Joseph Brown, a graduate student at the University of Michigan in Ann Arbor.

The study appeared recently in the journal BMC Biology.

Dating Methods

When dating biological events, molecular geneticists rely on a concept known as the molecular clock.

Over long stretches of time, mutations accrue, or "tick," at a fairly constant rate. By measuring the degree of genetic mutations, scientists can estimate how far back in time a species diverged.

Continued on Next Page >>




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