Re: Ptero notes (long):

["James R. Cunningham" <jrccea@bellsouth.net>]

David Peters wrote:
> 
> I am still waiting for _one example_ of a deep chord wing
> membrane showing a forelimb-hindlimb linkage.

Me too.  However, I do think it is quite possible that some may exist. 
I just haven't seen them yet.


> >> and sesamoids on the extensor surfaces of either the
> hand or foot. These features, all indicative of tree climbing,<<

They can also illustrate a need for either increasing an extensor lever
arm, or adjusting optimum muscle contraction speed to extension speed,
or both.  Not necessarily related to arborality.  At the moment, I have
no opinion re arborality of early pterosaurs.


> It appears to me that the femoral head determines the typical angle of
> the outgoing femur. In some species, widely sprawling, in others much
> less so.

I think it may be controlled more by the angle of ankle placement on the
tibia.  The tibia needs to be placed so that the bottom of the foot is
approximately horizontal when on the ground.
> 
>  2. Does the tarsus in flight have its dorsal side up?
> 
> Again Jim wrote >> No.  ........they would point aft and very slightly down, 
> with > the spreading such that the 4th toe would be displaced (flexed) 
> further aft than > the 1st toe. 

> I understand what Jim is saying here. In pterosaurs with a spreading
> metatarsus digit I is on top and digit IV is typically stacked below
> proximally.

Isn't that digit order reversed?  With the leg spread out into flight
position, Four would be 'on top' and aft, and One would be 'on bottom'
and forward.  Camber is established by the relative aftward displacement
of Two and Three, AOA is established by the relative displacement of One
and Four and the angle of the tibia mostly as seen from the side, but
also to some extent as seen from the front. In cruise flight the foot is
quite 'nose' down (leading edge lower than trailing edge) as seen from
the side, and the ankle extension is about 160-165 degrees roughly as
measured from the long axis of the tibia. But the AOA of zero lift is
negative enough that the foot can lift to some extent even when
substantially 'nose' down.


> Distally this could lead to a "card spread" except that
> proximal articulations between the metatarsals appear to interlock and
> prevent this from happening to the extent necessary for the appearance
> detected in the illustration.

I agree with this. It doesn't spread as far as the illustration and the
tarsals don't spread as much as the deflected digits, but both spread
enough to perform their aerodynamic function.  The tarsal spreading with
ankle extension is quite noticeable.


> Rather the metatarsus appears to be
> variably spread in wading pterosaurs (and Anhanguera by descent),
> apparently narrow for flight, and widespread for wading.

I can't address all pterosaurs in this regard.  Only the ankle and foot
that I have seen manipulated myself.  And it spread further as the ankle
was extended, being considerably more narrow when the ankle was flexed
into terrestrial position.

> As Jaime
> correctly noted, the pads faced caudally in flight in all pterosaurs.

No, not quite caudally.  This is affected by both the offset angle
between the tibia and the foot that allows the foot to be horizontal
when in terrestrial position and by the angle in which the femur (and
therefore tibia) is carried in flight as seen from the side.  The knee
is carried slightly higher than the hip when seen from the side, and the
ankle somewhat lower than the knee.  Consequently, the pads have a
distinct caudo-ventral angle. Mostly caudal but some ventral component
apparent.

> The metatarsus in Anhanguera, you'll note the foot and especially the
> metatarsus is extremely reduced, no doubt because Anhanguera spent
> little time on the ground,

I don't follow.

> ..... Still trim tabs don't have to be big.

I do follow that part of it, and agree.
> 
> ..... so only a toe spread  in the vertical plane (when
> flying) is possible.

Now, that's not true.  All the toes don't have to be deflected equally
at their proximal joints (or more distal joints either).  In flight
position, if the 'top' toe is deflected more, it moves further aft
relative to the bottom toe and the chord line of the foot changes
correspondingly.  Again, think beaver.  They are doing much the same
thing with their toe deflections.
> 

> Jim said >> Yes.  The aftward flexing of some of the toes to form an
> airfoil would be a variable and transient feature<<
> 
> I was actually thinking about the effect a metatarsal spread in the
> vertical plane, but flexing the toes backward is easily accomplished.

And necessary for the trim function to work.

> 5. What is happening to the fuselage fillet seen on most pterosaurs? It
> > seems to disappear or become unnecessary in the present model in which
> 
> > the knees are brought anteriorly close to the elbows?
> 
> Jim wrote: >>I don't think it is absolutely necessary, but it may still
> be there and
> likely is in a number of species.  It could help with flow control. <<
> 
> Perhaps upon landing? When the hind limbs might be extended differently?

Perhaps, but equally likely during cruise flight, for the same reasons
that wingroot fuselage fillets are important in aircraft during cruise
flight. Even so, not all aircraft have them and it may be that not all
pterosaurs had them.