Saturday, May 8, 2010

* Molecular Evidence - continued (2)

Let's take a closer look at this subject.
Here is the reference to the study that I mentioned earlier:
"A second molecular study robustly supported the relationship of birds to dinosaurs, though it did not place birds within Theropoda, as expected. This study utilized eight additional collagen sequences extracted from a femur of Brachylophosaurus canadensis, a hadrosaur.[4]"

And here is the abstract of the study itself:
"Fossilized bones from extinct taxa harbor the potential for obtaining protein or DNA sequences that could reveal evolutionary links to extant species. We used mass spectrometry to obtain protein sequences from bones of a 160,000- to 600,000-year-old extinct mastodon (Mammut americanum) and a 68-million-year-old dinosaur (Tyrannosaurus rex). The presence of T. rex sequences indicates that their peptide bonds were remarkably stable. Mass spectrometry can thus be used to determine unique sequences from ancient organisms from peptide fragmentation patterns, a valuable tool to study the evolution and adaptation of ancient taxa from which genomic sequences are unlikely to be obtained."

The important point is that the molecular evidence did not place modern birds within theropoda. To appreciate the significance of this we need to look at the groups within dinosauria:

Here are the claimed taxa within dinosauria:

Superorder: Dinosauria
Owen, 1842
Orders and suborders

A little cross beside a name indicates that that group went extinct and did not descend to modern animals. Notice that all groups, except Theropoda (and subcategory Aves) have a little cross beside them.

So if modern birds did not descend from Theropoda (and the molecular study indicates they did not), then modern birds did not descend from dinosaurs at all. There is no other dinosaur category that modern birds could have come from, since all the others went extinct.
Modern birds did not descend from dinosaurs, they developed from pterosaurs.

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