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Re: BADD BCF



In a message dated 95-12-05 23:02:00 EST, ornstn@inforamp.net (Ronald
Orenstein) writes (in reply to my comments):

>>The semilunate carpal is a winglike characteristic of dromaeosaurid
>>forelimbs. Remember that the wings of _Archaeopteryx_ retained a good
>>grasping function; the digits were all separate and movable (although there
>>may have been ligamentous locking mechanisms that kept them extended
>straight
>>when the wings were being flapped). So a flightless descendant of
>>_Archaeopteryx_ or a similar dino-bird would likely have retained the
>>grasping function, too.
>
>OR: the semilunate carpal is a feature of dromaeosaurid forelimbs retained
>in Archaeopteryx that proved to be important in the evolution of the avian
>wing, though it did not serve that function originally.
>
>Now: how do you tell these views apart?  How do you test them, other than
>finding more fossils?

The semilunate carpal is but one feature related to flying that appears in
_Archaeopteryx_. If the semilunate carpal were all there was, then I wouldn't
even try to concoct a different scenario for bird origins from the orthodox
one. But BADD expects me to swallow the conjunction of many different
supposed "exaptations," _each_ arising for some reason unrelated to flying,
in a single lineage where, miraculously, they produce a flying dinosaur! This
is nuts. It makes much more sense to me to envision these "exaptations"
arising in turn in a lineage as incremental improvements to a volant
lifestyle of some kind (just what kind--climbing, gliding, lousy flying--is
not yet clear).

>>The main problem I've always had with the BADD/ground-up scenario is
getting
>>a 20-50 kg theropod with relatively small forelimbs to evolve into a 2-5 kg
>>dino-bird with grasping wings. It _could_ happen, but in my opinion it is
>>_far_ less likely than having a 2-5 kg dino-bird with grasping wings to
>>evolve into a 20-50 kg theropod.
>
>I may be ignorant here but I have never heard anyone claim that the
>ancestors of birds weighed 20-50 kg - only that LATER non-avian maniraptors
>did.

I saw an article in _Discover_ several years ago in which they illustrated
flying birds evolving directly from _Tyrannosaurus rex_! Good grief!

>Why couldn't both lines - the avian and non-avian - have evolved from
>a smallish ancestor?

Because "both lines" is not necessarily the best picture. There weren't
simply two lines--avian maniraptors and non-avian maniraptors; there were
lots of different lines of both. There were archaeopterygid maniraptors,
dromaeosaurid maniraptors, avimimid maniraptors, mononykid maniraptors,
troodontid maniraptors, tyrannosaurian maniraptors, enantiornithine
maniraptors, and so forth. BCF says that the ancestral forms of all these
lines themselves form a line, the line leading to the more modern avian
maniraptors.

>Also - though it is perhaps more common for size to increase with time there
>is no rule that it need do so, and dwarfism can evolve relatively rapidly
>(eg the pint-sized insular elephants and mammoths known from various
>islands).  Also close relatives can vary considerably in size, so an
>ancestral line could have closely related large and small forms.  Consider,
>for example, the bird family Phasianidae, whose members range in size from
>Coturnix chinensis (12-15 cm in length) to things like Pavo muticus at
>190-250 cm (without the train); the size range in hawks is even greater,
>from the male Tiny Hawk (75 g) to the female Harpy Eagle (7600-9000 g).

Right. Under special circumstances of territory or resource deprivation (for
example), dwarf forms will evolve. What special circumstances were there over
the entire planet that caused Cope's Rule to be systematically violated
during the entire length of the Jurassic Period? Of course Cope's Rule is no
rule--just a guide--but when it is broken, it is usually for interesting and
unusual reasons. I'm willing to listen to anything. And I'm not talking about
the random variations in size you will always find among the species in
taxonomic groups, each of which probably has a very specific, individual
cause.

It is simple to envision in general terms the evolution of a large,
flightless bird such as _Diatryma_ or an ostrich from a smaller, volant form,
even though the details may not be available in the fossil record. What
evolutionary steps would something like a _Diatryma_ or an ostrich have to
undergo in order to produce a (small) flying descendant? Can you document an
occurrence of this kind of evolution? If you can, I'm certainly interested in
hearing about it, because then I would be much more willing to accept the
evolution of a (small) flying descendant from a larger theropod.