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Re: Pterosaur hand and wrist musculature



I tend to think the pteroid is likely a neomorph, but whatever the origin,
my response is actually about pteroid mounting, articulation, and
secondarily, musculature.

In Quetzalcoatlus species, there is a rather clearly delineated and somewhat
raised 'socket' on the locally thickened medial side of the lateral distal
syncarpal, located about midway down the side of the LDC from the
antero-dorsal cotyle that mounts a sesimoid.  When the pteroid base is
placed in conjunction with this medially directed 'socket', the shape of the
socket and the base of the pteroid are a perfect match both when the pteroid
is directed medially and throughout an articulation to a somewhat
antero-medial position.  When in this position, there are markings around
the 'socket' that align with similar markings on the base of the pteroid.
There is also a longitudinal groove on the anterior face of the pteroid base
that aligns with a transverse depression in the antero-ventral surface of
the LDC.  The shape of the LDC groove is quite reminiscent of the groove for
the tendon that carries the tensile loads underneath the elbow in both Qsp
and Qn.  This is consistent with a load path from near the inboard end of
metacarpal IV to the base of the pteroid that would give the pteroid a very
active roll in swinging a partly folded wrist forward and holding it there.
This also implies that one of the major pteroid articulations is a swing
from medial to antero-medial and that the pteroid is also carrying some
upload.  There is also some ability to also rotate about the long axis of
the pteroid (offset to the base, so providing some camber control). Other
markings near the base of the pteroid imply an active ability to swing the
pteroid between the medial and antero-medial positions.  Since they align
with anteriorly directed projections on the proximal carpal and the radius,
they could help move the outer wing forward and hold it there.  In addition
to swinging and holding the wrist, this would give the pteroid an  active
role in controlling flutter during high speed flight and when the wing is
partially retracted during the flapping upstroke. In Qsp, there is a 'hard
stop' on the medial side of the LDC that limits the medial deflection of the
LDC with the distal carpal. Again, this implies substantial tensile loads
across the front side of the wrist.  In side view, the shape of the LDC is
consistent with an appropriate airfoil shape at the wrist, and it obviously
defines the camberline at the wrist.   Note that in Quetz, the pteroid
cannot be directed antero-ventrally.

 If the pteroid is a neomorph, some of these attachments may be neomorphs as
well, or perhaps modifications of earlier ligament attachments between the
bones of the wrist?

All the best,
JimC

John Conway wrote:

> What do people think happened to the tranversus palmaris and flexor
> digiti quinti in pterosaurs (presuming digit V is lost, and not the wing
> finger)? Also, presuming the pteroid is a neomorph -- not digit I or
> metacarpal I -- what muscles were available to control it?
>
> Any refs on this would also be appreciated (better yet, PDFs, as I lack
> university access at present).
>
> P.S. Feel free to ramble on about pterosaur digit identification.
>
> ..........................
> John Conway - palaeontographer
> http://palaeo.jconway.co.uk