- Jun 5, 2003
All alligators, crocodiles, caymens, etc. are archosaurs, like birds and dinosaurs. It's like moles, whales, bats, etc. are all mammals and more like each other than they are like birds or crocodiles.Maybe I’m not understanding what you meant with your original claim (re-quoted above) correctly because I’m just not seeing your response as supporting it in any way. So to clarify;
Is it your claim that through scientific observation someone can rightly observe that an alligator (for example) is more like a pink flamingo (a bird) than it is like a crocodile?
You see, both mammals and archosaurs are a diverse group with a lot of different body shapes and ways of making a living. But in each group, genetic and anatomical data shows them to be descended from a common ancestor. This is how Huxley, over a hundred years ago, predicted that there would be transitional forms between dinosaurs and birds. Some key features in the skulls of birds and crocodiles made that clear. Later on , we have confirmation of that prediction.
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, or so-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.
That's 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. That's 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.
"The DNA in the modern-day crocodile has changed a lot less, versus the archosaur, than it has in birds," said Haussler.
By comparison, bird DNA took flight. Their pace of molecular evolution accelerated, and within about 15 million years of evolution, birds radiated out into the bulk of the existing 36 modern avian orders.