[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Flightless bat? Flightless pterosaur?

John Bois (jbois@umd5.umd.edu) wrote:

<A commonsense explanation for this is that they no longer need to fly
from predators-->wing muscles are expensive to maintain-->w/out selective
advantage for them, other factors weigh heavier, e.g., in times of little
food, the leaner machine is selected (not needing to
maintain--feed--flight muscles). Surely the same advantages should acrue
to bats (or pterosaurs).  So why so few?  Maybe this has to do with the
difficulty of escaping from vestigiality.  Walking, for bats is
vestigial--meaning that while they still might do it, the flight function
has so co-opted their limbs for flight they may never be efficient
walkers.  In birds, rear legs are not (primarily, at least) involved in
flight--they are not vestigial walkers. And, note that _no_ completely
flightless bats or pterosaurs are known.>

  You may mean, no obviously incapable flighted birds? One might call kea
flighless enough, but they, like tinamous, do not preferrentially fly very
often, and one could not tell from their bones whether they were flighted
or not, potentially. However, after presenting an argument that may be
testable, we are faced with a [preferred?] argument. So, let's look at the
first argument: flightlessness in birds arises from lack of predation.
This is true only on islands, where the birds species are relatively
isolated, and rare from mammals. Fossil remains are always Recent, or
Quaternary at the oldest. Seldom do we get Pliocene or Pleistocene Pacific
island fossils. So, if we find fossils of bats or pterosaurs in deposits
we know were prone to making small, isolated islands, perhaps we can infer
they should be flightless or nearly so, and that predator species should
be rare, or absent, so that flight need not be maintained as a defensive
mechanism. A proposed alternate to diet must also take place, because what
was available by flight before, including foraging distance, is now much
more severely limited. So, we have fossils, age, geology identifying a
small landmass, and paleoecology to identify prey/predator species, and
investigative paleontology/paleobotany to identify potential food
recourses, or shifts in resources (seldom done for dinosaurs/pterosaurs is
a isotopic technique done for various fossil ungulates and the leading
evidence for the known Miocene climactic shift, in testing diets of
horses, or for the post-Iceage extinctions in camels, horses, rhinos,
  This gives us the other theory presented, and that's relative
vestigialization in bats to explain inability to shift to a terrestrial
life, but the recent posts have shown this is not nessecarily possible to
predict, as a living bat is often found on the ground, more apparently
than in flight. A living sloth can walk and swim, but its anatomy is
indicative of a suspensor, and has become adapted to that; does not
preclude its ability to locomote otherwise, however. Pterosaurs lack
vestigialization of the extremities and can, in fact, be described as
having the opposite, protraction of limb bones even if the relative value
of bone length is reduce to other bones, including their wings. But so to
do preferrentially terrestrial/arboreal birds, in which, as in chickens,
nene, kea, and tinamous, the wings are merely relatively smaller, but not
_incapable_ of flight. Dave Peters made mention of the relatively short
wing finger in *Quetzalcoatlus,* but in this taxon the non-finger arm is
extremely protracted in length, and the leg is also long, so the
appearance of a wing-finger folded nearly inside the arm is entirely
applicable, and irrelevant to the nature of wing shortening; in fact,
holding of the humerus horizontally and to some degree with the elbow more
vertical than the shoulder should force the wing finger to express a
length greater than that of the elbow+radius+carpus+wing-metacarpal, which
*Q.* expressed naturally (as Jim Cunningham) has expressed [and hopes to
do so futher in publication---hurry that up, Jim!].

  We have many means to assess flightlessness in extant animals and the
correlates they offer to other, flighted species, to test ... in extant
and likely recent taxa, for which biogeography and geography in general
are known. Less so is it possible to determine the case in older fossil
taxa. It is entirely possible that some species of pterosaur preferred not
to fly more than to do so, as in tinamous, and we have _no_ means of
testing this statement, and so it fails to be a scientific, if still
possible, hypothesis. Thus I refused to exemplify further when I stated
that there may be flightless bats and pterosaurs. Unless they were
wingless or with such a reduced wing structure, we shall never know. Only
azhdarchids are known with such short wings, and Cunningham, among others,
are showing they can STILL fly and it is possible to do so with smaller
wings and larger body masses. I swear, the surprises in the fossil record
are still there to surprise us. And this with *Hatzegopterus* deriving
from a relatively small landmass likely no bigger than Ireland,
Madagascar, or Iceland.

Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

Do you Yahoo!?
Yahoo! SiteBuilder - Free web site building tool. Try it!