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Re: Microraptor hanqingi, new species from China.



Habib, Michael <MHabib@chatham.edu> wrote:

> Wouldn't the evidence in this case just be comparative studies of arboreal 
> adaptations?  Not sure what else it could be.  We don't have any non-avian 
> theropods handy to throw into a
> tree (wouldn't that be fun, though, if we did?  Theropod chucking.  New 
> sport).


As I see it, the usage of modern analogs for the incipient stages of
avian flight (whether flying lemurs or chukar partridges) is that it
is often a case of pounding square pegs into round holes.  It would be
nice if extant species could emulate incipient arboreal or aerial
behaviors in pro-avians (or their relatives).  But it may not be the
case.


> Like Scott, I find your model of arboreal refugia quite reasonable.  I'm 
> wondering, though, what testable predictions your model would make compared 
> to, for example, a model that
> posits entirely terrestrial habits for paravians.


I also find the idea of the use of trees as a refugium very
attractive.  But the construction and testing of the roosting
hypothesis is especially daunting because (as Kris as pointed out) the
fixation of dyed-in-the-wool arboreal characters may have come long
after the expression of incipient arboreal behaviors by
terrestrial/cursorial theropods.  This makes things very tricky.


> I think the roosting/resting concept has serious merit, but I'm not sure how 
> to go about demonstrating it has serious merit more formally (thought 
> experiments and scenario building are
> fun, but not terribly useful).


The other problem with the roosting hypothesis is that what little
fossil evidence we have indicates that winged non-avian maniraptorans
slept on the ground (i.e., the sleeping posture of _Mei long_).


There is a limit to what science can tell us.  We can use techniques
(biomechanics, taphonomy, phylogeny, etc) to rule in or out certain
scenarios based on the available evidence.  But we may never be able
to reconstruct with confidence the stages that led to avian flight -
including the degree of arboreality in pro-avians and their relatives.


> Also, for all of the individuals in the current thread: we should be sure to 
> give good cause at each step for putting paravians in trees to begin with. 
>  The potentially intuitive nature of
> arboreal proto-flight does not constitute good cause.


I think the morphology of the "wings" of many paravians (e.g.,
_Microraptor_, _Anchiornis_, _Xiaotingia_, _Archaeopteryx_,
_Jeholornis_) is supportive of 'gravity-assisted' aerial behavior.
But two caveats: (1) a so-called "trees-down" origin of flight does
not necessary equate with arboreality in avian ancestors; and (2) I'm
happy to be proven wrong on my interpretation that the aerial
behaviors of these paravians only involved descents.







Cheers

Tim