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Re: Deinonychus Morphological Variations within Ontogeny



Thanks Jaime (and Jason) for your detailed responses.  I'm cognizant
of the importance of cartilage in defining motion at the joints.
Holliday's work certainly drives that home.  However, at the same time
I don't think we should understate the importance of the skeleton in
flapping flight.

What I'm trying to avoid is the tendency of some people (nobody here
of course) to extrapolate sophisticated flight behaviors of modern
birds onto non-avialan theropods.  The osteology and inferred
musculature of non-avialan theropods indicates that these animals
couldn't fly like modern birds.  This also applies to basal birds such
as _Archaeopteryx_ and confuciusornithids, and probably _Sapeornis_ as
well; their flight capabilities fall well short of those of modern
birds (judging from the pectoral skeleton, musculature, and feathers
too).  No amount of cartilage can change that.

There is a temptation to view all modifications on the theropod line
leading to birds as somehow "flight-related".  To return to how this
thread started, I'm not sure the features of juvenile _Deinonychus_
are flight-related at all; other (non-flight) possibilities should be
considered.  This applies to maniraptorans in general.  In fact, after
reading Allen et al. (doi:10.1038/nature12059) I wonder if the
increasingly 'crouched' posture in maniraptorans might be more closely
associated with decreasing body size (miniaturization - DOI:
10.1126/science.1144066) and scansoriality rather than with aerial
locomotion.  But that's just a whacky idea I have - I'm quite happy to
be refuted.

On Mon, Apr 20, 2015 at 12:05 PM, Jaime Headden <jaimeheadden@gmail.com> wrote:
> Tim Williams wrote:
>
>>>Irrespective of this crucial consideration, it nonetheless
> seems that the glenoid orientation was very different between
> dromaeosaurs and crown birds.
>
> Not sure about that. There's work underway in some limb joint studies
> to assess the actual relationship of bone to cartilateg, and of what
> type of cartilage. That would be Tsai's work on archosaur hips, via
> Holliday Lab, and others, including work through the RVC with John
> Hutchinson and others. While mechanical properties of bone alone can
> be assessed, there is a hidden relationship with types of certilage
> and their loading regimes that impacts how far we can infer bone
> alone, to say nothing of its relation to ontogeny. Do smaller, lighter
> animals need the same types of bone, cartilage density, tissue,
> attachment relationships as larger? Adult versus juvenile?
>
> The question is not seemingly so simple.
>
>
> On Sat, Apr 18, 2015 at 8:01 PM, Tim Williams <tijawi@gmail.com> wrote:
>> Jaime Headden <jaimeheadden@gmail.com> wrote:
>>
>>> Note that for many joint reconstructions, cartilage and other tissues
>>> influence limitations and permissions that differ from the shapes of
>>> the bone articular surfaces. In the case of some joints, this can be
>>> much higher than otherwise seems. In the shoulder and hip, especially,
>>> in crocs and some birds these joints are very, VERY different in form
>>> from their bony portions. This matters.
>>
>>
>> Certainly.  Irrespective of this crucial consideration, it nonetheless
>> seems that the glenoid orientation was very different between
>> dromaeosaurs and crown birds.  Even if dromaeosaurs (and
>> non-ornithothoracean birds) were capable of some form of flapping, the
>> evidence still points to powered flight arising quite late in bird
>> evolution - maybe close to the most recent common ancestor of
>> Enantiornithes and Ornithuromorpha.  So even after the impact of 'soft
>> anatomy' is factored into joint reconstructions, I'm highly skeptical
>> of any dromaeosaur (juvenile or otherwise) being capable of powered
>> flight.
>>
>>
>>
>>
>>
>> Cheers
>> Tim
>
>
>
> --
> Jaime A. Headden
> The Bite Stuff: http://qilong.wordpress.com/
>
>
> "Innocent, unbiased observation is a myth" - P. B. Medawar (1969)