Re: fused/unfused scap/coracoid

[David Peters <davidrpeters@earthlink.net>]

That's the answer I was looking for! Thank you, Jaime.

dp



"Jaime A. Headden" wrote:

> Dave Peters (davidrpeters@earthlink.net) wrote:
>
> <I notice in some primitive diapsids (Protorsaurus and kin) that the
> scapula and coracoid are fused. This pair becomes unfused then fused again
> a few times in daughter taxa. Any thoughts on why this does or doesn't
> happen, especially in these early diapsid sprawlers?>
>
>   Fused scapcoracoids occur in crocodilians as well, and also in many
> lacertilians. This is either an example of translating forces from one to
> the other (the coracoid is "in line" with the scapula and related to the
> abductor muscles that worked in direct, parallel opposition to the
> adductors of the scapula above the humeral glenoid) or by resisting
> stresses during stroke. This occurs in other quadrupeds, including
> sauropod dinosaurs, some terrestrial crocodilomorphans, and iguanodont
> dinosaurs. The L- or V-shaped conjoined scapulocoracoid complex of some
> pterosaurs has some relation to that of crocodilians, but not that of
> birds, and may not relate to flight per se, bus specialization related to
> mechanical loading and muscle effect angles and effects on bone when
> exerted.
>
>   However, is there a correllation between angle and fusion in pterosaurs
> for which partial fusion, complete fusion with obliterated sutures (as in
> azhdarchids and pteranodonts/nyctosaurs), or even simple loss of the
> synovial joint? This may have NOTHING to do with phylogeny if this is a
> mechanical feature relating to flight, or loading.
>
>   Cheers,
>
> =====
> Jaime A. Headden
>
>   Little steps are often the hardest to take.  We are too used to making 
> leaps in the face of adversity, that a simple skip is so hard to do.  We 
> should all learn to walk soft, walk small, see the world around us rather 
> than zoom by it.
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
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