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Re: Flightless pterosaur indicators



I think perhaps reduction of the forelimb skeleton and musculature is
also even less very likely to occur (and thus flight less prone to be
lost), if the forelimb is the principal generator of force during
locomotion.
As far as I understand your quadrupedal launch hypothesis, Mike, the
forelimbs, because of their greater capacity of exerting force, would
be used for the launch. Then, it was possibly the principal locomotor
organ also in common quadrupedal locomotion. As far as I know, this is
the case in vampires (I do not know, but suspect so in the case of
other bats).
One may see forelimbs reduced in some members of lineages as
dinosauromorphs (obviously and relevantly, including birds), where the
primary ground propeller is the hindlimb, but it seems less likely in
a group where the principal propeller is the forelimb, as may be in
the case of bats and pterosaurs...
If this is the case, forelimb reduction would be as difficult to
expect as parieasaur-like trunk shortening in limbless snakes.
Some study on pterosaur quadrupedal locomotion mechanics may be very
good for this argumentation line...

About waterborne pterosaurs, the hindlimbs seem fleeble any way, so
perhaps it would be also the forelimb the principal propeller. The
forelimb should reduce to become a good penguin-like flipper, so this
can act against flying capacity... But also against ground locomotion.
So, the animal may have to be exclusively aquatic. This is not even
seen in birds, where generally there is an alternative mode of
locomotion, less so in bats, as far as I know. Its trunk is somewhat
rigid, so unless this changes, it would have to be restricted to a
marine turtle-plesiosaur-like mode of locomotion. In this case
hindlimbs should reduce in lenght also in order to avoid turbulence...
I think many changes in proportional development of parts would be
required to make the pterosaur an obligate waterborne animal, as with
the obligate terrestrial scenario.