[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Flight capablities of Archie & Confucius? Not so good...
> > It is perhaps significant that kakapos are
> > flightless, but still use their wings to parachute to
> > from trees etc without getting hurt. For all that can
> > said, Archie had a better wing loading than a kakapo.
> Kakapos, though, are superb climbers.
> But I take your point. I suspect that the wings of
> _Archaeopteryx_ and small non-avialan maniraptorans (e.g.,
> microraptorines, _Rahonavis_, _Jinfengopteryx_) were
> employed to help get them out of trees.
No, not trees. What I mean is that the ability to parachute/glide safely down
from *any* significant elevation that can be reached is apparently so
advantageous that it is lost last in neoflightless lineages. Kakapos use trees,
because they climb very well. _Threskiornis solitarius_ used hillsides, because
it lived on a mountain and could not climb at all.
So perhaps it was also gained first in incipiently volant lineages that had
short, round wings with weak rectrices (as Archie had).
The basic technique is actually quite common in highly volant theropods too.
Owls, harriers, kiskadees, corvids and so on use it to pounce upon prey from a
lookout position (which need not be more than a meter above ground) with
minimal energy expenditure and minimal warning.
Lilienthal's hang glider experiments are really something to be considered as
an analogy. Check out this photo:
He had a launch-hill built that was elevated above the surrounding landscape by
about two times the glider's wingspan. For Archie, that would have been between
half a meter and a meter. Lilienthal's glidepath was up to 40 times the
glider's wingspan. That cannot be compared to Archie of course except in very
loose terms, but it would still mean that Archie could, from a rock or trunk or
coralhead or *anything* it could hop/scramble using hands and feet/WAIR up (no
real vertical "climbing" necessary!), achieve a glidepath that covered a dozen
meters or so[*], possibly in less time than it could run that distance, and
certainly with far less noise and energy expenditure.
To a contemporary observer, that would have made Archie the pinnacle of
efficiency. To its prey, it would have been a most dangerous predator. To its
predators, it would have been a most frustrating prey.
But perhaps Percy Pilcher is a better analogy than Lilienthal, as Pilcher tried
to evolve his gliders for powered flight but couldn't do it - the weight added
cancelled out the lift gained. Major structural changes would have been
necessary. Just the same as it was with Archie vs. later self-powered birds.
(John J. Montgomery, probably most familiar to US listmembers, was not very
keen on using ground-based launch)
It is also important that any significant Archie predators were terrestrial.
Small mammals do not use elevated lookouts today as much as they could, because
of the aerial threat. But even so, except for the smallest, they do so -
marmots, prairie dogs, black-footed cats, meerkats and so on. Even with no
flight capability at all, the advantage gained by using even the slightest
elevation to get a better view of your surroundings is immense.
It is a better null hypothesis to assume Archie did use elevated lookouts too,
than to assume it didn't, given how widespread and phylogenetically
noninformative such behavior is among animals of comparable size even today,
under more adverse circumstances. And as soon as it did get up somewhere, it
would have been in the perfect position to maximize the usefulness of its
marginal flight capability.[**]
In essence, that would make Archie (and anything with a similar anatomy) a
* I can find no published reference for estimates of Archie's glide ratio. A
good study would now be more important than ever, and I think a rather accurate
estimate can be made, given the quality of the fossil record. But it is really
important to consider ground effect, because there would not have been an easy
way for Archie to get out of it - with no significant vertical-climbing ability
nor powered-flight capability, it would have by default been largely limited to
the ground-effect zone, where the glide ratio is (IIRC) better. (Lilienthal,
Pilcher and Montgomery all found it problematic to get out of ground effect,
and it may be significant that Pilcher suffered fatal structural failure and
Lilienthal fatally stalled just above the ground effect zone)
** That such an approach is very useful even to perfectly volant theropods can
be seen when approaching birds resting on a slightly elevated position, e.g.
seagulls on breakwaters. If yo do not run at them but approach at a slow but
steady pace, they will usually choose to glide some distance away, rather than
flying up and leaving the area for good. There is little point in expending
energy for powered flight as long as simply putting some distance between you
and the disturbance by a far more energy-efficient way will do.