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Re: Pterosaurs and ABSRD (sensu Williams)



Heinz Peter Bredow wrote:



Feduccia wrote in his "The
Origin and Evolution of Birds" that Longisquama, Scleromuchlus and
Megalancosaurus were a disparate group of "avimorph archosaurs" from which
birds are descended. In "Nonavian Feathers in a Late Triassic Archosaur"
(Nature 2000, vol. 288) Longisquama's integumentary appendages were
interpreted as nonavian feathers propably homologous with avian feathers. So
now it's nonavian feathers in a non Archosaur.

Firstly, thanks for the kudos.

Secondly, you are entirely correct. The basic principle of ABSRD is that fossils are assessed according to how they "fit" a pre-conceived scenario on how birds (and bird flight) evolved. It's a conclusion in search of supporting data. Feathered theropods cut little ice with the ABSRD crowd because they _just know_ that birds evolved from a small, gliding arboreal non-dinosaurian archosaur (or archosaur-like diapsid) which evolved feathers solely for the purpose of flight.

I happen to agree that the ancestor of birds was a small archosaur with gliding and tree-climbing abilities. But, heck, why couldn't it be a theropod dinosaur? You don't have to be a "cladist" to recognize the overwhelming similarities between _Archaeopteryx_ and deinonychosaurs.


But I concentrated on the fact that Longisquama as kind of a chief witness
for ABSRD isn't even an archosaur as claimed by Feduccia, Ruben, Geist and
Martin. So if Longisquama would be a possible ancestor for birds it would
make birds also derived prolacertiforms. Thus making birds and pterosaurs
sister taxons!!!


Believe it or not, there is at least one DML contributor who believes that birds and pterosaurs are indeed sister taxa! (It isn't me.)

In a previous post in which I "ranted" against the philosophy behind ABSRD, I mentioned three of the above four persons, since they are the names most publicly associated with opposition to birds evolving from theropod dinosaurs. The next day I received a very terse post from one of the aforementioned persons (and since he does not subscribe to this list, somebody must have passed my message on.) So, Heinz, you have been warned! :-)


Tim

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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