lpetrich

In effect, some of birds' dinosaurian amcestors had reinterpreted their fingers as they grow; reinterpreting fingers 2, 3, and 4 (index, middle, and ring finger) as fingers 1, 2, 3 (thumb, index, middle finger). A reinterpretation that has been faithfully preserved in the only surviving dinosaurian lineage.

MrDarwin

My prediction is that the interpretation of the embryological development of bird digits will turn out to be wrong. The interpretation doesn't seem to be as clear-cut as Feduccia et al. would have us believe.

scigirl

Well, hmmm.

From <a href="http://www.sciencedaily.com/releases/1997/10/971027064254.htm" target="_blank">the first link</a>:

So, dinos had all five digits, which means they had the genes that coded for five digits. Then they go on to say,

By altering the gene expression, the same way that the dinos started out with 5 digits in utero, but only really developed 3. I don't see this as a problem at all, but maybe I'm missing something.

scigirl

Edited to add: Plus, do they really know what was going on in embryonic development for the early birds? You can't always infer the embryo from the fossil. . .

[ May 29, 2002: Message edited by: scigirl ]</p>

lpetrich

But does the Wagner-Gauthier digit-reinterpretation hypothesis seem reasonable?

I think that the ultimate test will arise from locating the molecular mechanisms responsible for controlling hand development; location of such mechanisms elsewhere has already resolved one major riddle -- the Geoffroy St. Hilaire dorsoventral inversion between annelids and arthropods on one side and vertebrates on the other. The hypothesis of a connection would be periodically revived -- and then picked apart each time. However, discovery of molecular mechanisms of dorsoventral patterning has generally been considered to strongly clench it.

Basically, the internal organs are arranged

Arthropods, annelids:

dorsal
heart
gut
CNS
ventral

Vertebrates:

dorsal
CNS
gut
heart
ventral

CNS = central nervous system

The ancestor was likely only a simple strip; the arthropod/annelid CNS has a ladder shape with a ganglion at each joint, while the vertebrate CNS is tube-shaped. And it was such dissimilarities which had caused the earlier rejection.

lpetrich

I think that the embryonic development that they are talking about is present-day embryonic development.

The Wagner-Gauthier reconciliation of 1-2-3 vs. 2-3-4 goes as follows:

Early dinosaurs:

1 -&gt; 1
2 -&gt; 2
3 -&gt; 3
4 -&gt; 4
5 -&gt; 5

Some early theropods:

1 -&gt; 1
2 -&gt; 2
3 -&gt; 3
4 -&gt; 4
X (digit does not grow)

Some later theropods and birds:

X (digit does not grow)
2 -&gt; 1 (first digit from low end)
3 -&gt; 2
4 -&gt; 3
X

In effect:

Digits start to form
Some digits may be supressed
Digits differentiate, with the low-side one becoming 1, the next one becoming 2, etc.

[ May 29, 2002: Message edited by: lpetrich ]</p>

ksagnostic

That's it! My anomic aphasia strikes again.

Once again, I certainly do not want to give the impression that I advocate dismissing "out of hand" what Feduccia or anyone else says on this matter. I can maybe evaluate 10% to 20% of what any professional in a relevant field says on this matter. However, in field's that I am better qualified to evaluate, I have learned that it is indeed good to "know your players". If other paleontologists or known figures in other related fields, who were known to be more neutral to the dino-bird question, were to indicate that given evidence made them question a dino-bird link, it would probably get my attention more.

[ May 29, 2002: Message edited by: ksagnostic ]</p>

Jerry Smith

God, I wish I had gone to class instead of staying up all night playing Spades at GIT.

You folks are the best - providing a slacker like me with a free education.. all of you.. thanks!

Jerry Smith

For you Brits - that's Georgia Tech. For you Americans, it was only the AP's bias that kept us from being #1 in '90 - my freshman and (alas) final year....