patagia, etc.

[kpadian@violet.berkeley.edu]

Darren Naish is certainly entitled to his opinion, and the net should be a place
where free ideas can be exchanged.  It may be worth pointing out, however, that
dino-fandom, which is wonderful and healthy, can generate testable propositions
when it enters the realm of science.  Those who enjoy crossing the line from
science fiction to science may wish to read on.

Pterosaurs were a really interesting bunch of animals, but to understand 
anything
about them one has to study allometry, phylogeny, functional mechanics, and
aerodynamics, as well as general paleontology.  Pterosaurs were not related to
"ornithosuchids," which are close to phytosaurs and the other pseudosuchians
(sensu Gauthier 1986); rather, they are ornithodirans closely related to dino-
saurs, and Scleromochlus is their closest outgroup (Padian 1984).  Ornithodirans
evolved from animals that were already small, bipedal, active runners with long
legs, as their synapomorphies show.  Through 150 million years of evolution,
pterosaurs NEVER altered the functional anatomy of their limbs toward any other
kind of locomotion, as far as preserved specimens show.  To claim that any set
of derived pterosaurs did differently requires a complete functional analysis,
which entails not only first-hand analysis of the specimens but also a detailed
testable model of what they actually did -- which has never been produced, to my
knowledge.
        Size increases in pterosaurs produced interesting effects.  Because mass
increases as a cubed function of any linear dimension, but wing area only in-
creases as a squared function, wing area must increase faster than mass in order
for wing loading to remain realistic; hence, shape changes with size.  This is
why the legs of large pterosaurs appear spindly; they are perfectly large when
compared to the torso (Padian, Carter, and Van Der Meulen, 1992).  
        As pterosaurs grew, they had two options to maintain bone strength.  
They could have retained proportionally thick bone walls, but to increase the
DIAMETER of the bone shaft, while retaining very thin bone walls, the shape of
these larger bones had a far more advantageous second moment of inertia, which 
is the crucial factor in resisting the stresses of flight (Van der Meulen,
Padian, and Carter, 1992).  Hence, the appearance of the hypertrophied fore-
limbs of large pterosaurs is an optical illusion:  they are all "mailing tubes
and styrofoam," as Don Baird used to say.
        Where did the wing membranes attach?  Difficult question, in view of
the fact that the functional morphology of the hindlimb is so generally in-
variable among pterosaurs.  So far, no studies of pterosaurs with wings
apparently attaching to hindlimbs have analyzed taphonomy.  Why for instance
would the Vienna Pterodactylus have membranes that attached to the BONES of
the thigh?  David Peters produced a quite reasonable alternative explanation of
the classic Sordes specimen in a recent reply in NATURE to Unwin and Bakhurina's
paper.  If there are other specimens supporting one claim or another, they have
not yet been described.  
        Why did pterosaurs retain functional hands?  Well, let's put it another
way. Why didn't they evolve hooves, if they were quadrupedal?  :)
        All this is meant to suggest that simple inspection of artists'
reconstructions of pterosaurs is hardly enough to decide questions of their
paleoecology and functional morphology.  However, a good painting does more to
show us how realistic or unrealistic an idea is (assuming the illusration is
correct) than thousands of words may.  So with the above caveats, I tend to
agree with much of what Darren Naish says.  The next step for Dino-Netters is
to couch this stuff in testable hypotheses and show us which research directions
to take next! -- kp