How Dinosaurs Evolved Into Birds: It Wasn't Quick or Easy

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/ Source: Live Science

A revised view of the dinosaur family tree suggests birds didn't evolve in one fell swoop from their reptilian ancestors. Instead, our feathered friends evolved very gradually, at first.

Researchers say their new pedigree of carnivorous dinosaur evolution is the most comprehensive one ever assembled. The analysis shows that birdlike features such as wings and feathers developed slowly over tens of millions of years.

But once the bird body plan was complete, the group underwent a burst of evolution that produced thousands of species, according to the study published Thursday in the journal Current Biology. [Images: Dinosaurs That Learned to Fly]

"It's basically impossible to draw a line on the tree between dinosaurs and birds," said study co-author Steve Brusatte, a paleontologist at the University of Edinburgh. But at some point in the development of birds, "something was unlocked, and they began to evolve at a supercharged rate," Brusatte told LiveScience.

Scientists have long known that birds are part of the dinosaur lineage. But because the fossil record has many gaps, some scientists and members of the public thought a missing link might exist between the first bird and its closest dino ancestor.

To address the "missing link" question, Brusatte and his colleagues analyzed more than 850 body features in 150 extinct species of birds and their closest dinosaur relatives. The resulting evolutionary tree indicates that the characteristic features of birds evolved very gradually about 150 million years ago, and the earliest birds would have been indistinguishable from their closest relatives. In short, no missing link.

The label of "bird" is somewhat arbitrary, but scientists consider the feathered fossil Archaeopteryx to be the first of the group, Brusatte said. "What probably distinguishes birds is the ability to have powered flight," he said, though it's possible that other dinosaurs could fly too.

— Tanya Lewis, LiveScience

This is a condensed version of a report from LiveScience. Read the full report. Follow Tanya Lewis on Twitter and Google+. Follow LiveScience on @Twitter, Facebook and Google+.