When it comes to DNA, crocodiles and birds flock together

If you really want to know about birds, you have to consider the crocodile.

That point was driven home this week with the release of the genomes of 45 bird species, which reassigned some perches on the avian evolutionary tree and included some seemingly odd bedfellows.

Down near the roots of that avian tree lies a mysterious ancestor that was decidedly more terrestrial and terrifying than the finch or the wren.

The archosaur, orso-called ruling reptile,roamed Earth about 250 million years ago, and was something that was very reptilian, very early-dinosaur-ish, and then it evolved into modern-day crocodiles and birds, said David Haussler, Scientific Director of the UC Santa Cruz Genomics Institute, a coauthor of several studies that came out of the avian genomics effort.

So it really is the proper dinosaur ancestor, Haussler said. And birds and crocodiles are the proper descendants of this ancestor.

Haussler isnt a fossil-digging researcher. He digs through genetic code. So does John McCormack, an Occidental College biologist who usually is plenty busy curating a collection of some 65,000 Mexican birds at Moore Lab of Zoology on the colleges Los Angeles campus.

But both researchers are keenly interested in a kind of living molecular fossil -- small strands of DNA, the code of life, that are shared among a wide array of species.

These markers are very nice for doing comparative genomics, because theyre so conserved. Theyre easy to find among organisms that are very distantly related, said McCormack. We can find them across all of these genomes, and use them to build a phylogeny -- an evolutionary history.

Thats where the modern saltwater crocodile, American alligator and Indian gharial come in. Those modern crocodilians are still crawling around with much of the DNA they inherited well before dinosaurs ruled and evolved into birds. Thats why McCormack and Haussler helped map out the modern crocodile genome, along with those of living birds. Their work was among 28 research papers published online Thursday, based on a four-year genome mapping effort.

They found the crocodile had the slowest rate of molecular change of any known vertebrate genome.

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When it comes to DNA, crocodiles and birds flock together