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

["Jaime A. Headden" <qilongia@yahoo.com>]

I wrote:

<<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?>

  Yes, inspite of the tail. Mind that this thing is quite narrow
and not rounded in section despite restorations, and the meat
and flesh may have followed this. No, it does not appear to have
been pneumatized, but that's largely irrelevant: a long
stiffened and solid rod produces the same effect as a hollow
one. If you're concerned about the weight, remember this is bone
and quite light. The tail of *Rhamphorhynchus* is stiffened
distally, modifed from the primitive condition in
*Preondactylus* where the chevrons are elongated but do not
overlap successive vertebrae (they are elongated in the other
direction as in *Dimorphodon,* *Rhamphorhynchus,* and
dromaeosaurid dinosaurs) with a vane ... this is an aerodynamic
structure, absent in this form in _any_ swimming animal, which
tend towards crescentic and much larger unilobate or bilobate
structures. But more on that later.

I wrote:

<<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:>

  Dippers are not aquatic birds. They are essentially fliers.
Birds do one thing to their wings when they become aquatic, and
for good reason: the arms becomes shorter. It looses the ability
to fly with them. The Great Auk, sphenisciforms,
hesperornithiform, etc. all have reduced brachial structures
that indicate the lack of flight. Only in these birds do we see
a primary aquatic mode of life. Any other birds that _can_ go
into the water, either to hunt with or not (such as pelicans,
cormorants [with the exception of the Galapagos species], auks,
dippers, skimmers, anhingas, etc.) are still fliers, and fly
well. The crappiest fliers are not aquatic birds, incidentally,
including phasianid galliforms (chickens), hoatzins, etc. That
these birds may be able to swim is irrelevant.

  Back to sphenisciforms. Pengins do an additional thing to
their wings that is paralelled in the fossil plotopterid
pelecaniforms and the Great Auk: they become robust. These wings
are still able to mechanically use the power stroke, but the
proportions have changed, and the integument is different. The
feathers have become shorter, stiffer, more sheetlike in their
morphology, and mechanically suited for moving through a more
viscuous environment than air. To _equal_ the power of a flier
in the air, the sphenisciform wing is much stronger, shorter,
and suited to make oar-like pulled through the water, instead of
wing-like sweeps in the air. The same for the tail, which is
stubbier, more robust, and kept to little retrices. These are
avian sculling adaptations.

  Rhamphorhynchids are essentially the opposite of this, the
center of gravity is not caudally located (presumably Ebel says
this because of the long tail, but does not elaborate based on
what you've presented); in comparison to *Pterodactylus* from
the same sediments, *Rhamphorhynchus* is actually as big or even
bigger in some cases, and the wing is approximated, though not
as narrow. What is interesting in rhamphos is the elongated
fourth finger of the wing, which compared to pterodactylids, is
ridiculously long; pterodactylids, on the other hand, elongate
the forearm and manus, but not the finger; it seems to get
shorter.

  Take one comparison specimen of each or study, and the ratios
of limb elements (using the humerus as the default 100% element,
others compared along that line):

         hum - uln/rad - car/metcar - dIV-1 -- 2 ---- 3 --- 4

Rhampho  100    128.7       63         126   212.5  110.3  171
Ptero    100    92.4       81.2       99.4     98    84     70

  Proportionately, the distal segments, as shown above, are
longer on the whole than that of pterodactylids, suggesting that
the flight performance was perhaps _better_ in the former than
the latter, a point which Ebel does not appear to elaborate on.
There is the feeding equipment in *Rhamphorhynchus* also to
consider, which indicates a surface skimmer, the jaws positioned
over the water as a skimmer (*Rhynchops*) or pelican to snap at
any prey that hit the lower jaw. This form of feeding would not
be workable under the water,and I cannot see how the jaws would
opperate in this fashion wheil under the water. If David or
anyone else can, please elaborate.

  David writes, citing Ebel:

<"Rhamphorhynchoids 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].">

  I have little respect for Ebel's hypothesis based on this very
set of conclusions: The stiffened bony tail is ridiculous in a
swimmer, as it restricts mobility: all swimmers I can think of
has a completely mobile tail. Cetacea went through a couple
million years development from *Pakicetus* to *Basilosaurus* in
formulating the now-well--known loose vertebral sutures in the
dorsal and caudal vertebrae so that the tail could move up and
down. All aquatic vertebrates also seem to have a side-to-side
caudal organ which requires the mobility of all the elements.
Not one is stiffened in the plane of movement. Not so
*Rhamphorhynchus.* The position of the distal "vane" in the tail
of *Rhamphorhynchus* is debateable, as only that taxon seems to
have had it as far as my researches have been able to determine.
The structure in *Sordes* appears to be a disparate set of bones
set in flesh that would have made an interesting tail structure
distally. The position of the "vane" is debateable, but one
would think, as in the Messel mammals and Yixian birds, any
structure like this would lie flat during deposition. The vane
may well have been vertical. You can't tell, and this comes from
Ebel's assumption that position in death is position in life?

<"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.">

  Lyrebirds and pheasants can fly as well as auks can, despite
long tails in the former two birds. Many birds of paradise,
scissor-tailed flycatchers (*Tyrannus*), and many
caprimulgiforms and countless hummingbirds have elongated tail
feathers that defy reason with _horizontal_ velae at the ends,
but to produce sounds for the most part. It should also be noted
that the same structures are found in some butterflies.

<"As a consequence of these skeletal modifications, the centre
of gravity experienced a considerable shift forward.">

  Yah, it's what I thought: He used the tail structure to assume
the position of the center of gravity, instead of looking at the
body.... The entire trunk is built for flight, and the COG would
have been between the shoulders, where the muscle mass of the
pectoralis, humeral muscles, supracoracoideus, etc. would have
tipped the body forward. This is secondarily adapted by the
shortened legs.

<"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.">

  Ebel is now ignoring the long trunk, short legs, and features
which suggest that anurognathids were more primitive than
rhaphorhynchids, choosing to interpret the short tail as
suddenly a mechanical feature linking it with
Pterodactyloidea....

<"The primitive airfoil section, compared to birds, suggests the
same conclusion.">

  Naw, the airfoil was as advanced as in birds, even including
the prescence of a bastard-wing analogue, power-stroke, and so
forth.

---------

  David writes:

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

  Yeah, there's one. Peters, 2000, in _Revista Italiana di
Paleontologia e Stratigraphia_ 106 (3). The abstract reads:

  "Traditionally, pterosaurs have been included within the
Archosauriformes and many contemporary workers consider the
Pterosauria the sister group to Lagosuchus, Scleromochlus and
the Dinosauria. New analyses cast doubts on those relationships
because nearly all presumed archosauriform or ornithodire
"synapomorpies" are either not present within the Pterosauria or
are also present within certain prolacertiform taxa. Recent
examinations of the holotypes of Cosesaurus aviceps, Longisquama
insignis and Sharovipteryx mirabilis suggest that many
characters may be interpreted differently than previously
reported. Results of several subsequent cladistic analyses
suggests that these "enigmatic" prolacertiforms, along with the
newly described Langobardisaurus, are sister taxa to the
Pterosauria, based on a suite of newly identified
synapomorphies."

  Peters, D. 2000. A Reexamination of Four Prolacertiforms with
  Implications for Pterosaur Phylogenesis. _Revista Italiana di
  Paleontologia e Stratigraphia_ 106 (3).

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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