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Re: hovering pterosaurs



HP David Peters wrote:
>
> I can say nothing about hovering abilities. But I would like to ask the
> following ?related question.
>
Alright, let me take a wack at it, it's always fun to speculate about the
lifestyles of prehistoric animals... :)
>
> There is one anurognathid with an enormously wide sternal complex and
> six elongated anterior dorsal ribs to brace it -- together with
> remarkably slender wing bones.
>
> There is another anurognathid with a very small sternal complex, only
> one set of dorsal ribs to brace it and remarkably robust wing bones.
>
> Wing spans are comparable.
>
> What can we deduce from such differences?
>
That these two genera had different lifestyles! Well, that would be to easy
I guess ;) Now for real: a strong sternum complex indicates an active flying
lifestyle. This is seen in extinct and extant birds, so apart from the
differences in their bauplan of the wing, some similarities are also to be
found. One is only needed of mentioning here: the sternum and a carina,
which is also seen in pterosaurs. Last time I checked, Feduccia reported in
his 1996 book that the carina on the sternum, as well as the sternum itself
was used to anchor strong flight muscles.

Strong flightmuscles, coupled with the relatively long wings that we find in
anurognathids, are indications of a lifestyle that includes tight cornering
in the obstacle-filled world near the jungle floor, using batwings as an
analogue. This holds for the anurognathid with the wide sternal complex and
the slender wing bones really well, add this information to the world it
lived in (I know which genus HP DP means ;)) and one can see why it would be
needing a fast turning ability.

A smaller sternum does imply a less active flying style, perhaps we are
looking at the anurognathid hypothesis argued in WWD. Holding on to the
backs or some other area of large dinosaurs and just to wait for the insects
or other small animals that also join in on the free cab ride :) An active
lifestyle of chasing their prey would not be needed, as was the full use of
the sternum. With the sternum now with a relatively limited function, it
would "desolve" or de-evolve to the point that it only was capable of doing
only the essentials, in this case, holding on to it's "cab."

Although robust wing bones can imply a hovering lifestyle, this lifestyle is
only usefull when you have the power to get enough lift from the ground/
tree that you can get into the right airflow that you can hover over the
landscape. Resulting from this quick lifestyle sketch, there are 2 things
that are really nessecairy in case you don't have strong flight muscles:
very high trees and an open space. Not to say that is was not available in
the prehistoric world ranging from the late Jurassic to the early Cretaceous
and that it was not possible to live this lifestyle, although it seems
unlikely in my eyes. If we do chose to go with the option of a hovering
pterosaur with the expected flora in this period, one can suggest the
following: a pterosaur that "fell" deliberately from a tree branche only to
employ it's wings during it's freefall, much like the use of a parachute.
Problem is though, that when you hover, it is nearly impossible to get any
higher than the area that you launched yourself from if there are no
airflows that will get you higher like in present day hoveringplanes or
hanggliders. This would mean that if a pterosaur wants to get hold of a prey
that was higher located than itself, it would have had to climb a branch
higher than it's prey and than to hover to it Evil Knievel style...
>
Cheers,

Rutger Jansma

ps. best wishes and the best of luck for the coming year!!!