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Re: polarity of bipedality in dinosaurs (real long--TOO long)
At 01:16 AM 9/27/96 -0400, Dinogeorge wrote:
>Certainly not, if your wing design includes feathers or featherlike
>structures that extend backward from digit II over digits III-V. Bats and
>pterosaurs did not have feathered wings; they had membraneous wings, which
>makes quite a bit of difference to the shape of the airfoil and the digits
>involved in it.
You cannot demonstrate that the wings had to have formed "from digit
II over digits III-V", so therefore you cannot argue that the loss of these
fingers is assoicated with this feature. I think that if you started out
with five fingers, you could form the wing over digits IV and V or just V,
as I stated in the last post, in which case you would end up with a
different manual structure. Why, oh why, would they necessarily *START*
flying with a structure which would then require them to reduce the fingers
*under* the wing when they could start with the feathers anchored *farther
back* and be rid of the entire question, as pterosaurs did?
>It's evolutionarily not very easy to get rid of unneeded body parts. This
Hey, that's my line!
>goes for digits as well as the appendix.
And yet, you yourself point out that there was strong selective
pressure for birds to lose those other fingers. Yet, according to your
theory, they still hadn't lost two of them until the early tetanurans radiated.
Which brings up another point... If your hypothesis is true, and
all of the dinosaurian groups appear when they do because of the order in
which they split off from the "dinobirds", how come most of the earlier
forms (eg. ceratosaurs) have *very small* fingers. If, as you pointed out,
most theropods tried to make the baest use they could out of their reduced
hands, you *wouldn't* expect coelophysoids to have their _fingers_ reduced,
you'd expect them to reduce the hand and keep the fingers the same "volant"
Bear in mind, I dispute more than a few of the assumptions behind
this argument, so don't nobody go flaming me for it. I'm trying to argue
this one on George's terms.
>But when "flight began," that is, when the earliest theropodomorphs
>began gliding and otherwise controlling their trajectories in the
>trees, they still had all five manual digits.
A) You have no fossil evidence to back up this sweeping statement.
B) See above, then why don't long-fingered theropods show up until
>Don't be a wise guy. You know I mean serially V, then VI, then III, instead
>of symmetrically about the axis of the hand, I and V reducing together.
I can't help it, George, I'm emulating my betters.
Read my text. I know exactly what you mean, and I still say that
serial reduction of fingers can only lead you to the conclusion that
dinosaurs are vertebrates. Although, do recall that the thumb *is* somewhat
reduced. But that is not the point. V-IV-III certainly *is* well within
the parameters of normal vertebrate evolution. What do you think happenned
to digit VI (which you wisely included in your above text)? And digit VIII?
>This is almost certainly because the small forms preserve better in Mongolia
>(different geology and taphonomy)
I am not convinced of this. The Mongolian fauna seems to have more
animals at the extremes (although the ornithomimids are puzzling...). In
any case, you cannot seriously think that there cannot be seleciton
pressures for smaller size. We all know that there are inherent survival
advantages to almost any size range. Why is it so hard for you to believe
that a new species may simply find smaller size more convenient? For if
size reversal were extremely rare or unreversable, we would have a definite
lower limit on the size of vertebrates today. The only lower limits we see
are those imposed by vertebrate structure (ie. we do not expect to find
tinier vertebrates in the past, due to postulated biological limitations).
>> Uh... *I*N*SU*L*A*T*I*O*N* comes to mind...
>Yeah, well, somebody needs to demonstrate that dinosaurs were endothermic and
>>required< insulation to retain and regulate body temperature. Be my guest...
No, you simply need to prove that they had a feathery coat. I don't
>require< an apendix, but I have one, we don't know why Diplocaulus
>required< it's weird head, but we know it had it. I can prove that many
dinosaurs did, and still do have a coat of feathers. (Andrew Lloyd Weber
comes to mind...)
Where did that coat come from George? Even them darned "Safki"
things which have exapted (if I keep up this 10 cent word business, I'm
gonna take Cnadice Bergen's job at Sprint) their hair for its aerodynamic
properties had to have that hair before it could be exapted. So were from
came the feathers?
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| Jonathan R. Wagner "You can clade if you want to, |
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