Re: Bird evolution

[Stanley Friesen <sarima@ix.netcom.com>]

At 10:59 PM 3/30/98 GMT, Leon Retief wrote:
>The February 1998 edition of "Scientific American" carried a good,
>very readable article by Kevin Padian and Luis M. Chiappe, entitled 
>"The Origin of Birds and their Flight."
>It states : "Anatomical and aerodynamic analyses of fossils and 
>living birds show that birds evolved from small, predatory 
>dinosaurs that lived on the ground"

They make a good case for point one, but their reasons for point two ("that
lived on the ground") are weak, at best.

The thorough bipedality of theropods does tend to support an arboreal bias
in the lineage.  And the arms and claws of various coelurosaurs are well
suited to climbing.

>evolved from dinosaurian anatomy. Objections to the dinosaurian
>ancestry are noted only to be shot down by seemingly convincing 
>arguments.  I enjoyed this article and thought that the whole 
>matter seems to be more or less cut and dried, or as much as 
>something like this can ever be.

>However, I then came across a book review in the March/April issue 
>of "The Sciences", in which Larry Martin reviews three books, by 
>Alan Feduccia, Sankar Chatterjee and Pat Shipman.
>Martin states : "In the great debate over bird origins, the 
>dinosaur connection is set to take a dive."

Yep.  He has been saying this since at least 1977, when he said something
similar to me.  (I graduated from KU, Martin's home port).

It is also interesting that he includes Chatterjee's book here, given that
Chatterjee comes down solidly in favor of a dinosaurian ancestry for birds
in his book.

>Martin also discusses the role of Ostrom in convincing 
>paleontologists that birds descended from dinosaurs, but states 
>that the pendulum has begun to swing back again, saying that new 
>evidence contradicting this view is beginning to emerge, quoting 
>two recent articles in Science which show that dinosaurs are 
>clearly distinct from birds.

Well, let's see.  He probably talks about the article that purports to show
that the lungs in _Sinosauropteryx_ are crocodile-like, not bird-like.  And
he probably mentions the article that purports to show the "fingers" in
bird embryos are a different set than in theropod dinosaurs.

Both have been extensively discussed here, and found wanting.  The supposed
diaphragm in _S._ may be an artifact of preservation, and the logic in the
other article is flawed - it requires a constancy of embryology that
theropods fail to conform to anyway.

And the newly described Italian dinosaur ("Skippy") seems to refute the
proposed reconstruction of the lungs in _Sinosauropteryx_, from what I have
heard.

>Martin feels that instead of being descendants of dinosaurs, birds
>should rather be regarded as cousins, descending directly from 
>dinosaur ancestors called thecodonts.
>In fact, Martin convincingly points out a number of apparent 
>fallacies in the arguments advanced by the proponents of the 
>dinosaur-bird connection, such as a seeming misunderstanding of 
>some anatomical aspects given much weight by Padian and Chiappe.

Hmm, could you elaborate on this?  What does he say?

>So then. What is one to make of all this?
>
Remember: Martin is strongly biased.

--------------
May the peace of God be with you.         sarima@ix.netcom.com
                                          sfriesen@netlock.com