Re: Microraptor also ate fish

[Tim Williams <tijawi@gmail.com>]

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

> -- Flattened central fingers do not show up until they are anchoring very
> long asymmetrical primaries, even after the later appeared on slender central
> fingered Archie, and when other powered flight adaptations are present,
> including bigger than usual fused sternal plates anchored via ossified sternal
> ribs. At some point the evidence for some degree of flapping flight just
> piles up to become the superior hypothesis.


It is a viable hypothesis, but not necessarily a superior one.
Alternative hypotheses deserve equal time.


When a flight-related character present in modern birds turns up in a
non-avian theropod, it doesn't always mean that the non-avian theropod
could fly.  For example, it now seems that truncation and
coossification of the tail vertebrae (forming a pygostyle) originally
evolved for non-flight purposes.  The same may be true for the
"powered flight adaptations" you mention. One cannot dismiss the role
of exaptation in the evolution of many avian flight characters.


> -- Using higher arm versus leg length ratios to assess flight ability and
> flight muscle mass is tricky because a number of fully powered flight capable
> birds have very long legs relative to the arms -- flamingos being one
> example.


Don't forget that in the flamingo, as in all extant birds, the
hindlimb has to be longer in order to compensate for the altered
(subhorizontal) orientation of the femur.  So any comparison between
relative hindlimb length in modern birds and non-avialan theropods has
to contend with the different modes of stride generation.


>What really counts is arm length relative to the body (total mass being
> the best parameter if you can get it), plus size of sternum, furcula etc.
> Relative to body size the arms of Archaeopteryx and Microraptor are in the
> normal flying bird range (have published on this), unlike most other
> deinonychosaurs, including all the large ones whose arm muscle/total body 
> mass was
> very probably correspondingly lower than the sinornithosaurs. Sinornithosaurs
> had long legs relative to the winged arms because they too were big feathered
> wings of some sort or another.


Yes, I subscribe to that last point.  But I also regard the statement
"big feathered wings of some sort or another" as the crux of the
issue.  What sort?    :-)


> -- It is not close to circular reasoning. [snip]  The evidence for flat sharp 
> toe claws in ground
> dromaeosaurs is overwhelming and the burden of evidence is upon those who
> disagree, specifically strongly arced and sharp pointed keratin sheathes must
> be found for the thesis to be viable.


This argument cuts both ways.  Your (hypo)thesis is that strongly
curved foot claws are associated with arboreality.  So in your view
large dromaeosaurs (such as _Deinonychus_) will not have foot claws
that are as strongly curved as those of _Microraptor_.  But until this
can be tested empirically, you cannot dismiss the possibility _a
priori_ that large dromaeosaurs had strongly recurved foot claws too.
Maybe they did, maybe they didn't: we need more evidence.


Nevertheless, if _Microraptor_ did spend most of its time in trees, I
find the lack of a perching foot troubling.  Osteologically, the pedal
proportions of _Microraptor_ are strikingly similar to those of
_Deinonychus_.  Why would an arboreal theropod retain a short and
elevated hallux?








Cheers

Tim