bauplan convergence and stratigraphic data (was:100% goose-free responses)

["Scott Hartman" <scott_hartman@hotmail.com>]

John,
    I've been following your idea for a while now, and I'm finding it more 
intriging than my dino-chauvinist outlook would expect.  I do have a problem 
with two of your claims though:

1)>Why, if the dinosaur body form is so successful, doesn't it
> reestablish itself as the dominant form in the large-animal niche?  My
> answer to that is that it should.  I would say T. rex would kick >Serengeti 
> butt if brought back to life.  So, why hasn't it, or, >rather, something 
> like it, been brought back to life?  I think you >must be able to at least 
> suggest an hypothesis for that lack of >phenomenon--or, scrap the notion of 
> convergence!

    It's always seemed pretty apparent to me that true non-avian 
dinosaurimorphs never evolved after the K/T boundary because birds had 
derived too specialized a bauplan (has "bauplan" finally been put in the 
OED, by the way?)at the time of their extinction.  Not only the lack of 
teeth, but confluence of the orbit and lateral temporal fenestra, snout 
kinesis, and even increased encephalization combine to reduce jaw strength 
(important in large predators) as well as reduce the space available for 
muscle volume.  The lack of well developed digits probably didn't help, and 
nearly precludes a sauropod or large ornithiscian morphology.
    I'm not one to put too many constraints on evolution, but several 
ecological and deveopmental factors probably conspire to make sure teeth and 
non-avian forelimbs are gone for good (yes, I know some phororsurachids had 
"hands," but they're a poor excuse for a non-avian  maniraptoran manus).  
First of all, while enough of the structural genes for teeth are present to 
grow transplanted tooth buds under the correct stimuli, the regulator genes 
that control the expression of those structural genes are either a)gone, 
b)extremely reduced, or c)co-opted to control the expression of a different 
structural element.  Since "teeth" are useful enough that there are 
tooth-like crenulations known from some Cenzoic birds, but no examples of 
actual tooth reaquirement, I suspect that either a or c is most likely.  
This would most likely preclude tooth evolution in post K/T birds.
    Avian limb evolution is probably also largely constrained, although by 
ecological factors in this case.  Flying birds use their limbs for 
locomotion, of course, but because of such they always have (and probably 
always will) utilize their hindlimbs for terrestrial locomotion.  As 
terretrial locomotion becomes more important, and flight is lost, there will 
be a strong selective pressure to reduce the huge muscle and bone complex 
that supports flight, which would otherwise be a terribly wasteful portion 
of bodymass (and potentially degrade cusorial locomotion as well).
    Of course this kind of constraint depends entirely upon prevailing  
ecological pressures, so isn't absolute, ergo phororsurachids with "hands."  
But as arms are reduced, some of their regulator genes may also wander off 
or apply for different jobs, further limiting future limb evolution.  I 
suspect that the only way functional grasping nonavian theropod hands could 
re-evolve is in  situation where the forlimbs are important in non-flight 
locomotion while they are still useful for flight (e.g. a hoatzin).  And a 
quick gander at avian natural history (pun intended) shows you how often 
that happens.
    Maybe future hoatzin descendents will be entirely arboreal, and further 
develop their hands, while flight related structures are reduced.  I wish I 
could see it if it happens.  So even if the entire non-avian dinosaur 
extinction was caused by omlette loving mammals, the lack of extant 
dinosaurmorphs probably has nothing to do with egg predation.

2)Well, I used up more space with #1 then I had originally intended.  So 
briefly: I was going to object to using our current sample of K\T ecosystems 
as even preliminary evidence to support the idea of a non-catastropic 
extinction event.  I don't think we really have enough data to say one way 
or another yet, unless we are going to propose that dinosaurs nearly went 
extinct in the Middle Jurassic.

Alas, I would dearly love to see a tyrannosaur in the Serengeti...does 
anyone have ILM's number?

Scott
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