Re: Microraptor also ate fish

[GSP1954@aol.com]

In a message dated 5/1/13 6:55:33 PM, tijawi@gmail.com writes:

<< 

> 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.

-- As per previous discussions on the list, the argument that vertical 
humeral elevation is needed for some form of powered flight is very dubious. 
May 
well preclude strong flight climbing ability though. 


> 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.

-- Velociraptor does not have a flattened central finger to firmly anchor 
the more important distal primaries that microraptors do. The presence of 
flight features in large derived dromaeosaurs is the same pattern seen in 
secondarily flightless birds. It has never been shown that these features 
evolved 
before flight, they are very probably the result of flight. 


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.

-- The big dromaeosaurs did not have arm muscles as proportionally large as 
those of microraptors because the former have smaller arms (the humerus is 
half the length of the body in microraptors, much less so in Velociraptor) 
with smaller muscles. Only the Jehol dromaeosaurs have arms large enough to 
be muscled well enough for powered flight (maybe juveniles of big 
dromaeosaurs had some flight ability, would be nice to have some skeletons to 
see what 
is going on with them). 



> 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.

-- MY understanding is that the Jehol flora was conifer dominated and 
closed canopied, so there were mainly high canopies rather than cycad type 
fronds 
to fly up into. 



> 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_.


-- Keratin sheathes are never preserved in large dromaeosaurs, but the 
chance that they were as curved as those of microraptors is zero. All small 
terrestrial theropods and Mesozoic with preserved toe claw sheaths are low 
curvature, and no known bird incl raptors that spends much time walking and 
hunting on the ground has such strongly curved toe claws. The central toe claws 
of Veloci and Deino would have been fairly flat and probably tip worn, like 
those of ratites and secretary birds (looked at them in the Smithsonian 
collections - because their toe claws are blunt Secbirds pummel their prey to 
death, rather than try to claw pierce it).



> 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.

 >>

-- Again, no bird that moves much on the ground has strongly curved toe 
claws, they are always flattened. No known exception. The strongly curved toe 
claws of microraptors mean they were not habitual ground walkers. The big 
foot feathers would not be good for that either. Could do it if they needed to, 
but they were not adapted for it. 

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