Birds may have originated 40 million years earlier than previously believed

February 6th, 2008 - 12:38 pm ICT by admin  

Washington, Feb 6 (ANI): A new analysis by researchers has offered the strongest molecular evidence yet for an ancient origin of modern birds, suggesting that they arose more than 100 million years ago, not 60 million years ago, as fossils suggest.

Researchers at the University of Michigan, the University of Chicago, the Centre for Biodiversity Conservation Mexico and Central America, and Boston University, did the analysis.

According to Joseph Brown, who is first author on the paper regarding the findings of the analysis, “Scientists typically use two sources of information to date biological events: the fossil record, which contains physical remains of ancient organisms, and molecular genetic data.”

In the case of modern birds, however, the two approaches have yielded conflicting results, at times leading to heated debates between paleontologists and molecular biologists.

While molecular biologists have asserted that the fossil record must be incomplete, paleontologists have countered that the genetic data must be suspect.

In fact, both approaches have their weaknesses, said Brown. According to him, fossils tend to underestimate how much time has passed since lineages diverged.

As for genetic data, the so-called molecular clock isn’t quite as precise as once thought. The approach relies on the observation that although mutations occur at random in the genome, when looked at over long stretches of time they occur at a fairly constant rate. Molecular biologists use that rate to reconstruct evolutionary history.

The problem is, different lineages can ‘tick’ at different rates, so applying a single rate to an entire tree could lead to very suspect results,” said Brown.

Fortunately, new methods exist for compensating for differing rates.

“What my colleagues and I did was apply all of these new methods to the problem of the origin of modern birds, with each method making different assumptions about how mutation rate changes across the tree,” said Brown.

He hoped the analysis would narrow the gap between fossil and molecular data, but in fact it led to the finding that modern birds arose more than 100 million years ago. (ANI)

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