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Re: Feduccia (was: polarity of bipedality in dinosaurs)



At 02:07 PM 9/23/96 -0500, Ron Orenstein wrote:

>I have just purchased, and started to read, The Origin and Evolution of
>Birds by Feduccia.

        Lucky...

>1. the similarities between birds and maniraptorian theropods are convergent

        He's joking?

>2. animals like Velociraptor are too big, heavy and earthbound to be bird
>prototypes

        He doesn't understand how to read a cladogram?

>3.  anyway, they lived too late

        See above...

>4.  birds evolved from arboreal ancestors, and Velociraptor isn't the least
>bit arboreal.

        See Bakker.  I still don't see why dromaeosaurs couldn't have hung
out in trees.  Frankly, I wonder more about how little kids stay in trees.

>I probably shouldn't take him on this early in my reading, [...]

        But you will anyway... :)

>I thnk that point 3, in a way, cancels out points 2 and 4. [...]

        Cheers!

>Why should large terrestrial maniraptors converge in so many ways to
>small arboreal birds or protobirds?

        Note that this contradicts point number 2 above, as well.  A
fantastic point which no one ever mentions.

>Is Feduccia's problem that he cannot imagine an arboreal proto-maniraptor?

        No, he cannot accept that there is a tremendous body of evidence
against his theory.  I think he's still pretty spiffy, though.

>If so, I find this much less of a stretch than to imagine a long-bodied
>quadruped like Longisquama or Megalancosaurus turning into a short-trunked
>obligate biped like Archaeopteryx.

        Parsimony, if nothing else.  It develops twice or once, you
make the call.

>This raises the point I have made several times here (and that no
>one seems to want to discuss!) that gliding quadrupeds may be very
>poor models for bird ancestors, as the natural tendency in such a
>creature would be to keep the trunk lengthy and the hind limbs
>involved in the gliding surface in order to maximize the surface
>area of the gliding membrane[...]

        I'll discuss it when I can find a problem with it.  :)

>So why isn't it more likely that the "birdlike features" of
>Longisquama etc are convergences to birds (both are arboreal) and
>those of maniraptors represent true kinship, rather than the
>reverse?

        Because "dinosaurs have a big bulky pelvis that is unaerodynamic",
of course.  The ultimate test, as we all know from watching Paleoworld, is
the Martin test, where a cardboard cut-out of Archaeopteryx is compared to a
cutout of a dromaeosaur.  You will note that the archy cutout has a wide
chest, and the dromaey a narrow chest.  This should be sufficient evidence
to prove that the two are not related.

> Feduccia makes much of the comparative brain sizes of birds and
> maniraptors and ascribes this to arboreality in the former [snip]

        His evidence?

>[snip]if he is right, then all you have to do is suppose that the
>split came either just before or shortly after the bird ancestor
>became arboreal, with the convergences related to bipedality and
>enlarged brain size being a special feature of the bird line.

        Actually, all you have to do is use his point #4, "dromaeosaurs
aren't arboreal".  Why would they keep that big brain if they weren't.

>Feduccia illustrates a hypothetical protobird on p. 92, as
>long-bodied, rather sinuous glider.  I find it hard to believe in
>such a creature, though Feduccia seems convinced of it.  Am I
>missing something?

        Yes, you are interested in paleontology, not ornithology.

        Wagner
+--------------------------------------------------------------------------+
| Jonathan R. Wagner                    "You can clade if you want to,     |
| Department of Geosciences              You can leave your friends behind |
| Texas Tech University                  Because your friends don't clade  |
| Lubbock, TX 79409                               and if they don't clade, |
| znc14@ttacs1.ttu.edu                   Then they're no friends of mine." |
|       Web Page:  http://faraday.clas.virginia.edu/~jrw6f                 |
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