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Re: pterosaurs, bats, flying theropods



Original Message by John Bois
Monday, 23 December 2002 14:58

> On Fri, 20 Dec 2002, Jaime A. Headden wrote:
> > Other arguments seems to focus on
> > bats becoming nocturnal, to avoid diurnal birds, but this is similarly
> > bunk as it is first a generality (only most microbats are nocturnal), and
> > second there are plenty of diurnal bats (all megabats) and nocturnal
> > birds (owls, swiftlets, etc.) which live in the same areas as microbats.
>
> 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!

One should appreciate both the way things generally are and every single 
exception. Otherwise wrong explanations for both are easy to find.

> Niches are available to all body plans.

More or less.

> If one body plan (birds) dominates the diurnal niche to the
> extent birds do, we must admit this is not just a matter of chance: birds
> have it over microbats in the day time.

What about another idea: birds were already there in the daytime, and, in 
order to _avoid_ competition, most microbats stayed nocturnal. (Assuming 
nocturnal ancestors is of course not so easy to test, but nocturnal mammals 
are not exactly something rare, maybe this condition is the plesiomorphy for 
placentals.) The whole niche partitioning and competitive exclusion thing.

Then there are more complicated affairs. Several species of bats (most of 
Megadermatidae, and the false vampire *Vampyrum spectrum*, for example) eat 
terrestrial vertebrates, mostly but not only at night. They live all over the 
world's tropics, and I don't know how they coexist with owls. On the other 
hand, there are nocturnal insect-eating birds like goatsuckers, and they 
coexist with classical microbats.
        From 1982 to 1986, AFAIK, Fred Sinowatz was Federal Chancellor of 
Austria. 
His standard answer to journalists and everyone was "everything is very 
complicated". People loathed him for this. So far, I don't understand why, 
because the Sinowatz Principle has very few exceptions. :-)

> A prime
> hypothesis for investigation should be that bats are more likely to be
> prey in the day time than birds are.

Well. What could those diurnal predator be which could more easily attack a 
flying than a sleeping bat? I can only think of raptors. More manoeuverable 
species should have an advantage then... and bats are generally better at 
that than birds because they can change shape and camber of their wings 
anytime, using skin muscles. Apparently that's why they don't need an alula.

> Predation may also explain the relative immunity of megabats 
> and therefore their ability to forage at midday.

There are small megabats, too. What about *Syconycteris australis*, for 
example. Book says 5 -- 6 cm long and 12 -- 15 cm wingspan, as big as a hand.

> After all, feathered wings are likely not identical in effectiveness as
> non-feathered wings.  Which are better?

Depends strongly on what exactly you want to do with them, see above.

> And while bats and pterosaurs are
> disimilar in many ways, they are similar in this crucial aspect: they
> don't have feathers.

And, apparently, dissimilar in another crucial aspect: between the 
actinofibrils, there was no space for skin muscles, was there? Looks like 
that, having stiff wings with a fixed shape and lacking an alula, pterosaurs 
were limited to flying the ways swallows, swifts, confuciusornithids and 
albatrosses do/did it. Which of course is ideal for the inferred lifestyles 
of anurognathids and pteranodontids, for example.

HP Jim Cunningham wrote:

> For low frequency flapping, the
> membranes will likely win hands down, at least in pterosaurs.

Why in pterosaurs?