Diving pterosaurs? (was Re: Lemurs and Feathers) (long)

["David Marjanovic" <david.marjanovic@gmx.at>]

About 10 days ago, there was a thread on

Klaus Ebel: On the origin of flight in *Archaeopteryx* and in pterosaurs, N.
Jb. Geol. Paläont. Abh. 202 (3), 269 -- 285 (Dezember 1996)

which is the main ref for the through-the-water origin of flight. Now the
exams are over, and I've found time to answer to what HP Jaime A. Headden
wrote:

>   Sorry if this is crude, but we're supposed to think here, when
> data is presented before us. And I don't know how Ebel formed
> this concept, but rhamphorhynchs had quite cranially located
> CG's between the shoulders or just behind. The form of the trunk
> is telling in this, and rhamphorhynchs especially have very
> short hindlimbs,

Even despite the long tail?
Was the tail pneumatized?

> Nothing mechanical in the forelimb suggest the limb
> was used to scull or flap in water. It's is supremely adapted
> for _aerial_ flight.

I'm not sure how easily this can be told apart. I mean, dippers have AFAIK
no adaptation to water in their wings (they can fly, however). Well, here's
what Ebel writes, and I think there are some reasonable arguments in this:

"Rhamphorhynchoids [wrong, long-tailed ones] were not yet adapted to flying
in the air. The Upper Jurassic *Rhamphorhynchus* has still the long bony
tail of underwater flyers with a small vertical steering velum which could
hardly produce an effect when flying in the air [amazingly few people have
thought about this so far]. The situation did not change before the
appearance of [...] the pterodactyloids which apparently were no more
restricted to underwater hunting and flew exclusively in the air. Besides
further modifications, they did not only reduce their tail but also
lengthened neck and skull at the same time. As a consequence of these
skeletal modifications, the centre of gravity experienced a considerable
shift forward [...]. This change had adaptive reasons. During swimming under
water the exact position of the centre of gravity had not been of special
importance in *Rhamphorhynchus*, because the propulsive force passed through
it in any case [...]. However, when flying in the air the centre of lift was
positioned in front of the centre of gravity, leading to a moment that
hampered the flight capability seriously. The animal was flight-mechanically
unstable and could stay in the air only by permanent flapping. Gliding was
not feasible because of the labile balance condition. Shifting the centre of
gravity below or slightly in front of the centre of lift to generate a
condition of indifference or slight stability, in birds also the normal
situation, became an imperative necessity and decisive improvement for
flying in the air.
        This shifting of the centre of gravity led to a minimization of
steering forces, allowed a rapid reaction to disturbances, and thereby
guaranteed optimum manoeuvrability. Again, these modifications had their
first appearance [convergently to pterodactyloids!] in small forms such as
*Anurognathus ammoni* (WELLNHOFER 1993b [his big encyclopedia]). This
species represents an important [convergent] transitional type with
rhamphorhynchoid features as well as a short tail. Indeed, the shifting of
the centre of gravity can be regarded as good evidence that
rhamphorhynchoids were largely underwater flyers."

Here's how he has formed that concept -- from comparisons with Archie.

"However, if the complete flight ability was achieved only after the
modification had been completed, then the [long-tailed] rhamphorhynchoids
must have been very moderate flyers that were hardly able to rise high above
the water surface. The primitive airfoil section, compared to birds,
suggests the same conclusion. Obviously, flight was of little importance to
them. But if they flew it was easiest with prey in the beak, because prey
caused a forward shift of the centre of gravity, although the weight was
highest in that case. That hints at a possible pathway to the transition to
mere flying. Because of different lifestyles the differences between [...]
[long- and short-tailed pterosaurs] are more fundamental than supposed up to
now."

Here the paragraph that cries for HP Jim Cunningham :-) :

"Flying in the air and the occupation of new ecological niches by the
pterodactyloids became only possible after the completion of this
modification. A simple flat integument as an airfoil section would have been
sufficient only for small forms. Larger pterodactyloids had to modify also
the leading edge area and to fit it with a thickened cambered airfoil
section in order to avoid considerable flight restrictions. Although the
airfoil section was modified, the extent does not appear sufficient to allow
good performance. The reason may be that large types could specialize to
powerless gliding which was certainly their recipe of success. Soaring [...]
[is easy enough to tolerate slight misconstructions.] Restricted flight
ability of large pterodactyloids also follows from the 'design' of the wing
covered by a continuous integument which does not permit high maximum lift
coefficients and consequently does not allow the low speeds of birds.
Furthermore, the possibility of exercising an effect on the airflow by the
interplay of feathers was not applicable. Thus, for the minimization of the
induced drag, induced by the tip vortices, the wing had to be extremely
tapered. This led to an overproportional wing span, compared to birds, which
caused a restriction in the ability to take off from the ground, because
increasing wing span results in a relative decrease of the gap between wing
tip and the ground [sic]. [...]
        It is noteworthy and surprising that true flight ability was almost
simultaneously achieved by pterosaurs as well as by *Archaeopteryx*, by the
former following a long-lasting development [evolution] from the Upper Trias
to the Upper Jurassic, by the latter respectively her[*] descendants
relatively soon in the Upper Jurassic [I doubt it], probably because of an
altogether more favourable skeletal pre-disposition [such as an opposable
thumb] and [drum roll, hymnical music] by the epoch-making 'invention' of
the flight feather."

*As usual in lots of languages, but not English, Ebel keeps the female
gender of the word *Archaeopteryx*.

BTW, can I somewhere find a summary of the newest arguments for putting the
pterosaurs into Prolacertiformes (respectively as its sister group or
whatever...)?