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Re: Deinonychus Morphological Variations within Ontogeny



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)