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

Re: pterosaurs, bats, flying theropods

David Marjanovic wrote:
> Apparently that's why they don't need an alula.

Doesn't the thumb in some bats act as a functional equivalent to an
alula, just as fingers 1-3 of some pterosaurs do?

> And, apparently, dissimilar in another crucial aspect: between the
> actinofibrils, there was no space for skin muscles, was there?

Might want to double check that.  One way to do so is to look at the
typical actinofibril spacing per cm, and compare it to the average
diameter of a single actinofibril.  Also, it might be possible for
'skin' muscles to overlay the actinofibrils.

> 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.

What on earth would make one think that pterosaurs had stiff wings with
a fixed shape?  If they did, why would they have needed all the
structural specializations for controlling the aeroelastic number?

> HP Jim Cunningham wrote:
> > For low frequency flapping, the
> > membranes will likely win hands down, at least in pterosaurs.
> Why in pterosaurs?

Because during low frequency flapping, lift from unsteady flow effects
do not predominate, and the maximum steady-state lift coefficient for
pterosaurs is about 30% greater for pterosaurs than it is for birds and
40-50% greater than that for bats.  Pterosaurs appear to have a
steady-state CLmax of about 2.1-2.2.  Birds typically range from roughly
about 1.54-1.65.  Frigate birds have the highest avian steady-state
CLmax that I'm aware of, at about 1.63-1.65.  Bats range roughly from

Season's greetings to all, and best wishes,
Jim Cunningham