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Re: pterosaurs, bats, flying theropods



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

<One may argue with and ridicule pet hypotheses based upon extrapolating
extant behavior back to the Cretaceous.  However, one should not argue
that an extant, fully observable phenomenon, is not generally true by
arguing it's only a generality!>

  But, it is a generality. Only one select clade, Microchiroptera (which
is possibly polyphyletic with regards to Megachiroptera), is generally
nocturnal, with some dirunal microbats, and all megabats are diurnal.
Arguing that bats are nocturnal is in fact an error on the order of a
generality that does not hold true. Cats would be seen as diurnal hunters,
as all big cats are generally diurnal hunters to the possible exception of
leopards (*Panthera onca*), but this is also a generality, as most small
cats are nocturnal, and house cats are generally diurnal as a result of
their habitat. Thus it would seem to me an easily correctible error, and
this is why I argued against it.

<Niches are available to all body plans>

  But identical niches may not be available to different bodyplans. One of
the things I am arguing about, as was Jim Cunningham, is that the anatomy
of bats, birds, and pterosaurs are quite distinct from one another and
actually provide constraints. Animals that specialize to the nighttime or
even during crepuscular hours, have specializations to these in their
sensory anatomy.

<If one body plan (birds) dominates the diurnal niche to the extent birds
do,>

  But there is not but one avian body plan, but many of them. Owls,
oilbirds, nighthawks and goatsuckers, etc., have shortened faces with
large, forward facing eyes, and renowned hearing, good for nocturnal
living, with specialized feathers for making little to no sound during
flapping, good for night hunting, and all these have zygodactyle feet,
broad tail fans, and variably shaped wings. Soaring birds have reduced
flapping musculature and their arms are proportioned for flight, and
nearly all have webbed feet, alluding to their ancestry. And the list goes
on....

<we must admit this is not just a matter of chance: birds have it over
microbats in the day time.>

  What birds and what microbats? You cannot support this as there is no
actual competitive niche in which the two occupy the same space and the
same time. Without this, the effective significance of the relative
separation of these birds from these bats cannot in any way be established
as a performance superiority. How can not bats have outperformed the
birds? Does being diurnal mean something better than being nocturnal? How?


<And it's silly to say that bats just _give_ the day time to birds--they
would expand into this niche if they could.>

  Could they? I do not think anyone has ever been able to come up with a
suitable or even agreeable ecological mechanic in which birds and bats
arrived at their present distributions and ecologies as a result of
interacting throughout the Eocene--Recent timeline. If anyone can suggest
how any mechanic would have happened that agrees with the fossil record
and can thus be observed in anyway, I would love to hear it.

<Then we look at reasons why birds have it over bats. As you mention, they
both share a wide range of food resources; and it's hard to imagine that
one species could simply _out-eat_ a competitor.>

  Why not? Compared to the always-on-the-wing lifestyle birds have versus
bats, which fly for only a few hours of their life, or the more efficient
chiropteran digestive system, compared to the "slip right through me"
avian one, birds need to eat a lot more than bats do, have extensive
migratory, breeding, and competitive behavior, whereas nearly all bats are
closely associated, communal animals that share body heat, sometimes food,
etc.. We're also dealing with completely different animals, whose
comparative biology is different from their comparative ecology and
sociology. And that most bats tend to fall along similar lines, whereas
birds are extraordinarily far more diverse. You don't see many birds
exploiting some bat ecologies, either, such as chief nocturnal insect
eaters, or the "vampire" ecology.

  Cheers,

=====
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)

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