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Re: BADD BCF



GO writes:

>>This, however logical it may be, is not evidence.  If I understand you you
>>are saying that non-flying maniraptors share a suite of characters in the
>>forelimb that, in volant birds, serve as part of the flight mechanism, and
>>suggest that this involves too many coincidences to dismiss as anything
>>other than a secondarily flightless condition in those forms.
>
>In the forelimb (various modifications for a wing), in the foot (retroverted
>hallux), in the skeleton (pneumatization), and probably in the soft anatomy
>as well. Not to mention a number of less important but noteworthy cranial
>modifications, and flight feathers.

The retroverted hallux, as we have discussed here, is NOT a flight
adaptation.  It may be an arboreal adaptation (or not) - but that is not the
same thing.  Pneumatization (I think?) is also known in other dino lines
(sauropods?) and may serve other functions (air-sac type respiration,
lightening) that could either be flight adaptations or "exadapted" for this
purpose in birds.  "Probably" ain't evidence; the cranial characters may
indicate relationship, but what  does that have to do with flight?  And, yet
again, there is NO DIRECT EVIDENCE that ANY non-bird maniraptor had flight
feathers or any other kind of feathers.  A character state cannot be coded
because you think it ought to be there.

>When those characters _all_ involve modifications that significantly improve
>an animal's capacity for flight, I begin to suspect that they arose in that
>context.

This improvement (if present at all) could arise prior to the development of
flight - in fact some of these characteristics must have been present in a
non-fllying ancestor or flight would not have evolved!

>I'm dealing in likelihoods here--and in the unified picture of theropod/avian
>evolution that BCF presents. 

Likelihood isn't evidence.  Neither is  a "unified picture" (and I don't see
why BADD isn't also a unified picture).

>If theropods started out as cursorial animals, I
>would expect to see evolutionary modifications that improved their
>cursoriality, or their ability to use their forelimbs better for grasping and
>holding prey, and so forth.

It seems to me that an animal like Velociraptor is beautifully designed for
both, in many ways:  the balancing tail, the long grappling arms, the whole
build of the critter.    Again, I'm no palaeontologist - is there anyone out
there NOT committed to BCF who thinks otherwise?

 It is true that evolution sometimes hands us the
>unexpected, and to that extent I'm willing to entertain the idea that small,
>bipedal cursorial theropods acquired feathers (somehow), lost two or three
>manual digits (who needs 'em?), enlarged their grasping hands into grasping
>wings (for some reason), retroverted the hallux (well, why not?), etc., etc.

As I noted (much) earlier, even if these adaptations were evolved in an
arboreal ancestor that later became terrestrial this does not conflict with
BADD.

>>These are cautions, not fatal objections.  But the fact remains that the
>>only way to settle the matter is by discovery of further transitional forms.
>>For example, the absolute clincher for showing that, say, Velociraptor was
>>secondarily flightless would be an analysis showing that it lay WITHIN a
>>clade of known winged forms.  We do not have the taxa to show this.
>
>Actually, it does--Archaeopterygiformes. _Archaeopteryx_, _Deinonychus_,
>_Velociraptor_, and other dromaeosaurids share enough apomorphies that even
>cladists will soon admit that they belong to a single clade. The big problem,
>of course, is that only one (maybe two or three, if _Archaeopteryx_ comprises
>more than one species) of the known archaeopterygiform taxa was volant. But
>soon the Korean archaeopterygiform will be described, and there will
>undoubtedly be others.

This is not what I meant.  You must show that Deinonychus, Velociraptor et
al PLUS a winged taxon form a clade with ANOTHER winged taxon as the sister
group to that clade.  We are hardly in a position to do that.

My point was that the stem taxon
>>could have included quite closely related species diverging widely in size -
>>and, if so, could have given rise to both large and small forms.
>
>It probably did. So--?

Then you can't argue that size points away from BADD.  If the ancestral
stock included both large and small forms, otherwise very similar, then the
small form could have given rise to birds without size reduction, the large
form to larger maniraptors, and the whole group would still form a single clade.

>>But, as I said above, there is no reason to assume that BADD requires that
>>Archaeopteryx was derived from a LARGE theropod - only that both
>>Archaeopteryx and the large theropods like it evolved from a common ancestor
>>whose size is unknown.  Thus, unless you can produce a known ancestral taxon
>>acccepted as such by BADD theorists that is considerably larger than
>>Archaeopteryx, I think this particular argument is a straw man.
>
>This will never happen, because the BADD cladists weasel out of presenting
>_any_ taxa as ancestral.

I'd like to hear one of them on that.  So far the only taxon BCF has come up
with is Longisquama, which seems far too derived (and perhaps too distant)
to qualify (I mean, Eusthenopteron may be an ancestor too, but what does
that tell us?).  The point is that we do not have an ancestral
maniraptorian, and that is not dependent on whose theory you buy.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
Home: 1825 Shady Creek Court                  Messages: (416) 368-4661
Mississauga, Ontario, Canada L5L 3W2          Internet: ornstn@inforamp.net
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Toronto, Ontario Canada M5H 3P5