Re: Microraptor hanqingi, new species from China.

[Tim Williams <tijawi@gmail.com>]

evelyn sobielski <koreke77@yahoo.de> wrote:

> In and by itself, this is not necessarily absurd. Both trains of evidence may 
> be correct without colliding - any arboreal form that should happen to
>  descend from a cursorial-terrestrial form would necessarily evolve through a 
> stage in which well-developed cursorial plesiomorphies coexist with
> crude arboreal apomorphies, and the material evidence *could* be interpreted 
> thus in this case.


Granted.  But Gong &c do not interpret _Microraptor_ in this way.
They regard _Microraptor_ as a sprawling quadruped incapable of
terrestrial/bipedal locomotion.  I find this very difficult to
swallow.


> The hypermelanism also argues for a hot-and-humid environment and possibly 
> life under a closed canopy. So, the time and place are right for an
> experiment in arboreality. But this does *not* mean it was an *arboreal* 
> animal, at least if you don't assume natura facit saltus.


Yes, I agree.  A small theropod could venture up into vegetation
without qualifying as "arboreal".  This is one reason why the
arboreal-versus-terrestrial dichotomy is so unhelpful.


> However, that would require to accept the fact that "avoids" (I would write 
> "para-avians" but this is too close to Paraves for comfort) all
> descended from small cursorial-terrestrial theropods. There is nothing to 
> suggest that early archosaurs evolved towards arboreality, while early
> reptiles did so vigorously and early enough (they started off very, *very* 
> small and used low woody growth as it seems) to require an entirely
> different critter to result by _Microraptor_'s time. Something that had the 
> bauplan of a chameleon or _Draco_ perhaps. Not sprawling, but
> positively splayed.


There were large columnar plants around, even if they were not true
"trees".  The Late Permian anomodont _Suminia_ has been interpreted as
an arboreal herbivore.  Permian-Triassic diapsids like _Longisquama_,
_Sharovipteryx_, drepanosaurs, and coelurosauravids were most likely
arboreal.


But I suspect the erect/bipedal bauplan of _Microraptor_ and other
paravians was not so much due to differences in vegetation compared to
earlier times (although this could have been a factor), but to the
ancestry of paravians from among obligate terrestrial bipeds.  For a
creature that still spent most of its time on the ground, and only
occasionally ventured into 'trees", there was no reason to abandon its
cursorial adaptations.







Cheers

Tim