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Re: Yet more on pterosaur quad arm posture



Jason Brougham <jaseb@amnh.org> wrote:


> I've seen those asterices before. Tim cannot mentally accept that there is
> any stage in evolution between 'specialized for arboreality' and 'ground 
> dwelling'.


I can, in fact.  But perhaps this stage was relatively late in avialan
evolution - after _Microraptor_, _Archaeopteryx_, or even
_Jeholornis_.


Sapeornithids appear to have been bona fide perchers.  The perching
abilities of confuciusornithids appear to lie in between those of
basal-most avialans and sapeornithids (with the caveat that individual
confuciusornithid taxa show different hallucal proportions).  So maybe
confuciusornithids sit inside this transition between 'ground
dwelling' and 'specialized for arboreality'.


> Yet logic dictates there had to have been an enormous spectrum between the 
> two, in
> the history of evolution.


Yep, agreed.  But we can have have differing views on the phylogenetic
bracket that defines this spectrum.


> At least this time Tim did not declare absolute, supernatural, knowledge of 
> the
> capabilities of extinct animals, or declare any hypotheses to be dangerous or
> untestable (even when they were easily testable).


I can't recall any such declaration.


> Tim, what are your qualifications to declare other researchers' work invalid, 
> again?


I would typically never regard any other's work as invalid.  (Okay,
except the stuff from A. Feduccia or D. Peters).


I'm querying some of the assumptions that lie behind efforts to put
certain small theropods in trees.  This should not be interpreted as a
personal attack.  I read 'Dinosaurs of the Air' cover to cover, and
I'm still not convinced that _Microraptor_ or _Archaeopteryx_ were
arboreal.  I'm exercising my First Amendment right to disagree.


> Tim, It is a pretty basic principle of science that there is a far higher 
> standard of
> evidence to prove that something is  impossible than to defensibly state that
> something is possible.


There is a distinction between "impossible" and "likely".  I do not
think it is "likely" that _Microraptor_ was arboreal (sensu stricto).
I base this assessment on its anatomy.  But I cannot refute the
hypothesis that _Microraptor_ was arboreal in an absolutist sense: I
cannot say it was "impossible".


Similarly, I cannot say it is "impossible" that birds evolved from
crocodylomorphs; I just don't deem this to be "likely", based on the
available evidence.






Cheers

Tim