Re: Microraptor also ate fish

[Tim Williams <tijawi@gmail.com>]

Gregory S. Paul  <GSP1954@aol.com> wrote:

> The problem is that there is no way to ever sufficiently understand the
> flight performance of microraptors.


It also depends on to what degree the humerus could be elevated above
the dorsum, which in turn depends upon the orientation of the shoulder
joint.  No recovery stroke, no wingbeat, no powered flight.


> That it was a powered flier is the greatly
> superior hypothesis because it had so many adaptations for supporting fairly
> large arms muscles and anchoring the primaries, well beyond those found in
> Archaeopteryx which itself was beyond just gliding (I've discussed this in
> the literature and won't repeat it here because that is not the specific
> issue).


These interpretations aren't as simple as you make them seem.
_Velociraptor_ has quill knobs, suggesting that it had forelimb
feathers that were firmly anchored to the bone.  So firmly-anchored
feathers can't automatically be counted as a flight-related character.


And "large arm muscles" can hardly be a flight-related feature in all
theropods, considering that many theropods used their forelimbs for
catching and holding prey.  I don't dispute that powerful arm muscles
are essential for flight (!).  But we can't assume that this feature
originally evolved for flight in theropods.


> But could it climb well enough to get into tree
> canopies from the ground on a regular basis? Very possibly no, be we can
> never know.


I'm not clear on why the ability to penetrate tree canopies would
necessarily be so important.  Recall that at the time of the Jehol
biota, angiosperms were still getting off the ground, and
"cycadophytic" plants were far more prevalent than they are today.
The latter offered elevation and potential food sources, but little or
nothing in the way of shelter or refuge.


> What I do know is that having examined a number of big format photos of
> Microraptor central toe claws that were kindly supplied to me, that they are
> (using the recent published data sets and my own on a large set of predaceous
> birds) more strongly arced than the claws of any livng bird that reguarly
> traverses ground by walking hither and on. Only birds with weakly curved
> central toe claws walk and run a lot (I've sampled them, including the 
> raptors).


Is this pronounced claw curvature unique to _Microraptor_ among
non-bird theropods?  Or could a large dromaeosaur like _Deinonychus_
have the same or similar claw curvatures to _Microraptor_?  I think
it's helpful to look at _Microraptor_'s features in the context of it
being a predatory theropod, not just a bird relative.  As noted in the
literature, most of the vaunted "arboreal" characters in _Microraptor_
(including foot characters) are also found in _Deinonychus_.


> So Microraptor either used flight as it's main means of moving about from
> one place on the ground to another (doubtful in view of probably limited
> powered flight abilities, and probable lack of many open spaces in the Johel
> forests) or was primarily an arboreal climber (very probably, considering it
> lived in apparently dense woodlands).


I doubt that the lack of open spaces prohibited _Microraptor_ from
moving about on the ground.  It just meant that there was no point in
being highly cursorial.







Cheers

Tim