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Re: origin of birds



Paul R. Janke wrote:
 >
 > 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,

Oops, sorry about that.  I assumed, wrongly apparently, that
you tended to agree with them.

Does Ostrom *still* make that error?  I would have thought
he would reconsider his position now.

George Olshevsky has proposed that there were numerous small
arboreal dinosaurs, but we just don't have a fossil record of them.
This is at least possible, since the fossil record of "coelurosaurs"
is so abysmal.  Unlike with mammals, the teeth are not diagnostic,
and even if they were, they would not tell us if the animal were
arboreal, so the most common type of small dinosaur fossil cannot
answer this question.

Now, admittedly this idea is only speculation at this point,
and lacks any real supporting data, but it shows there are
possibilities.

 >... 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.

So is mine.

 >... 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.

O.K., that seems reasonable.
 >
 >
 > 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).

In fact, I believe there are some known "protosuchian" crocodilian
that may well have been bipedal.

 > Our only problem with these two conjectures is the lack(so far) of
 > supporting fossil evidence.

Well, Ostrom's list of shared features between Archie and theropod
dinosaurs still stands, so there is some fossil evidence.
 >
 > >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?

I certainly considered it, but only with reservations, and briefly,
because there seemed to be no alternative.  I quickly abandoned it,
long *before* Feduccia's paper on the perching adaptions in Archie.
I decided it was more likely that Archie had lost its arboreal
adaptions - like many ground dwelling birds today, than that
flight evolved from the ground up.

All Feduccia's paper did for me was to remove the need for
assuming a reversal in Archie, and to confirm that I had probably
been right in rejecting ground-up origin of flight.

But I tend to prefer giving other scientists the benefit of the
doubt on controversial issues like this.  In most cases if it
is controversial, it is *not* obvious.
 >
 > *Claws
 > [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.

The first is not really relevent, since modern ground birds have
all evolved from flying ancestors which had already lost the claws.

The second is a good point.  When was it first published?
 >
 > * 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.

Again, when was this done?  He had certainly not done this 10
years ago, the last time I spoke to him, or he would have mentioned
it to me.  [We were having a discussion about this very issue,
and he was trying to convince me Ostrom & co. were wrong].

You need to allow about a 3-4 year lead time for other people in
the field to evaluate evidence like this.

[Hmm, could you give me a citation on this, I think I missed
it, it sound like it is worth reading].
 >
 > * Flight Feathers
 > This is the _best_ evidence for arboreal lifestyle, as there is
 simply
 > no other plausible explanation for the origin flight in birds.

The problem is that this sort of begs the question, since
one of the issues is whether ground-up origin of flight is possible.

As I said, I quickly abandoned any idea of ground-up origin
after I carefully looked at the models.

 > 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.

Though they have suggested they used cliffs instead of trees. :-)
[I think this unlikely since such places would be rarer than trees].


Note, between Martin's and Feduccia's study, I think Archie's
arboreal status is now well established.


I still find Ostrom's proposed synapomorphies quite strong
evidence for an avian origin within the theropods, and indeed
within the Maniraptora.

[Note, despite that I still recognise Aves as a seperate class,
and continue to include dinsoaurs in Reptilia - I may accept
cladistic evidence, but I do not accept cladistic classifications].

swf@elsegundoca.ncr.com         sarima@netcom.com

The peace of God be with you.