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Re: origin of birds




Stan Friesen wrote:

> You again seem to be making the error that the theropod-bird theory
> requires a non-arboreal origin of flight.  One of the main points
> of my article is that it does not.  An arboreal origin is quite
> consistant with a theropod origin.

No Stan, Ostrom/Padian/Gauthier make that error, not me. When I make
comments about _their_ published theory, please don't attribute _their_
viewpoints to me. If you read my articles, you will note that I have
only talked about the published material and the related debate. For
the record, here is my personal view so you will have the opportunity
to _accurately_ state where I am wrong ;-) My personal view is that birds 
evolved from a tree-dwelling reptile.  As you may be able to infer from 
my posts, I have believed this much all along, inspite of the throngs
jumping up and down yelling "Hooray, birds _are_ theropods, the dinosaurs
are NOT extinct, etc." As to what reptile this might be, I'll put it this 
way: If I had $100 to bet, I would put $40 on theropod, $40 on crocodilian, 
and $20 on something else.
---

Stan Friesen wrote:

> I agree that the cursorial origin models were all a little strained
> and are well abandoned.

I agree, although I would use stronger terms than "strained" and remind
you that many scientists don't need to abandon anything as they never
bought it for a minute. Maybe I'm more inclined to give credit to those 
with a clear crystal ball on this one than you are? 
---

Stan Friesen wrote:
>
> In short, if pseudosuchian or protosuchian archosaurs could
> evolve arboreal forms from cursorial forms, so could the
> theropods.                                                   

Yes! It may also be wise to consider that if theropods can evolve 
bipedalism from a quadrupedal ancestor, so can a crocodilian(and others).
Our only problem with these two conjectures is the lack(so far) of
supporting fossil evidence.
---

Stan Friesen wrote:
>Well, the hoatzin-like claws are only obvious in retrospect,
>the presence of claws could equally simply have been a retained
>ancestral trait of little adaptive significance - that is they could
>have been vestigial.

>And, until Feduccia published his study there was little evidence
>that the footclaws were perching-type claws.  These things are not
>as easily determined as it might seem to the outsider.  I had to
>read Feduccia's article before I could evaluate the evidence,
>and despite Padian's opposition, I found his evidence quite strong.
>Again, just because Martin and Feduccia's gut feeling has now been
>largely vindicated does not make the non-arboreal idea retroactively
>unreasonable.   It is unreasonable *now*, but it was not so before.

Hmmm...Tell me Stan....Did you....ahem...buy into the cursorial theory...
..for maybe just a little while at some point?

Let's take a closer look at _some_ of the "gut feelings" you refer to. 
All this predates Feduccia, in some cases by decades.

* Claws
If one were to consider the possibility that Archie wingclaws were 
vestigial, the fact that Pterosaurs were known flyer/gliders with 
wingclaws should have sounded an alarm bell. Besides, Archie wingclaws 
seem far too articulated to be merely a vestigial trait. They were are 
highly curved and the fossils show that they had extremely sharp 
points. The toe claws are less curved, but were also sharply pointed, 
ideal for climbing up tree trunks. 
[relevant facts] - Birds that live on the ground and run on two legs 
have _no_ wingclaws and have _very_ worn toeclaws. All of the toeclaws
on Archie fossils are very sharp.

* Posture
The most accurate skeletal reconstruction ever done by a scientist 
was done by Larry Martin. He discovered that Archie seems to have had
a primate-like, upright posture. It should be noted that this came as
a surprise to him at the time, as all restorations he had published
prior to this study used the more traditional theropod-like posture.
The upright posture is an arboreal character in Archie just like it
is in tree-dwelling primates.

* Flight Feathers
This is the _best_ evidence for arboreal lifestyle, as there is simply 
no other plausible explanation for the origin flight in birds. When
the first wing membrane of a Pterosaur was found, it was immediately
cited as an arboreal character and remains so to this day. Nobody has
ever suggested that pterosaurs evolved flight by running and flapping
along the ground.

The same arguement applies to Archie with respect to flight feathers. 
The arboreal arguement can be traced to G. Heilmann(1926) and was actually 
considered the "conventional" theory until Ostrom (1970's). I believe that 
the misinterpretation of cladistic analysis by Padain et al was the primary 
cause of the mass-hallucination that was the cursorial theory. Although
they cornered the market on _quantity_ of evidence, they were somewhat
lackluster on _quality_ of evidence. All of these cladists have contributed
greatly to our knowledge of natural history, I don't mean to demean them
in any way. I do predict that the cursorial theory will be to them in
posterity what the cosmological constant is to Einstein.


* And now we have the latest Feduccia study...