[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Large last gasp of pterosaurs
John Bois wrote:
> > It
> > seems likely that there was a period of several weeks at the boundary
> > when conditions were unsuitable for soaring flight. After that, voila
> > -- no pterosaurs, but some continuously flapping birds survive.
> > Flap-gliders don't.
> Here is where I think circular thinking creeps in: Catastrophic mass
> extinction is evidence of a hostile environment created by the
> bolide-->pterosaurs became extinct at the same time so it must have been
> because of the hostile environment. I don't think you can have both be
> evidence for each other, can you?
I don't recall mentioning the bolide impact above, but don't object to
the implication that it was connected to a weather change either. But I
also don't see the circular reasoning. I don't think the demise of the
pterosaurs caused the impact. :-)
Essentially, I do think the impact triggered a period of weather
unsuitable for soaring flight. Pterosaurs in general were unable to fly
continuously by other means. If they can only 'crow hop', they don't
feed. If they don't feed, they don't survive. That's not circular.
Note that 'crow hopping' is intended in the sense of GA jargon, and has
nothing to do with hopping crows.
> This might be an ignorant question, but: how does any particular method of
> flying enhance a bird's/pterosaur's competitive ability?
It's not an ignorant question. The method of flight impacts the amount
of energy that has to be produced by the animal in an effort to cover
his territory (to stay aloft while feeding or traveling). This further
impacts a lot of other things, required aerobic capacity, basal
metabolic rate, relative proportions of aerobic and anaerobic muscle
tissue, the amount of food required, the amount of food (fuel) burned
during a flight (a soarer can cover more geographic area on less fuel
burn while searching for a gas station -- more food). Its sort of like
the advantage that a person with a Volkswagen has over a Humvee owner
relative to the contents of their wallet. Find a niche where you can
search a larger area than the competition while simultaneously needing
less food to do so seems a definite advantage to me. Think about the
interface between the flight mechanics and the biomechanics. Colin
Pennycuick has done good work on the subject.
> I understand
> about vultures being able to stay aloft, and eagles diving on prey--but
> how do you see this in relation to Q. and would-be bird
See above. Also think about the competition between vultures and
> Albatrosses are large and have a large range, geese--I suppose I mean the
> ability to stay aloft for a long time--w/out stopping. Is this relevant
> to Q.?
No more than it is relevant to hummingbirds and butterflies, both of
which are capable of crossing the Gulf of Mexico nonstop. As an aside,
geese use a very different means of traveling than Q and will burn off a
larger fraction of their body weight while doing so.
> > I'm saying that all midsized to large pterosaurs were relatively immune
> > to some causes of extinction that might apply to small pterosaurs.
> Which causes? Reproductive failure? In extant species predation (in
> birds, particularly during reproduction) is the primary limiting factor,
> not head to head competition for food.
You're making the implicit assumption that pterosaurs are more subject
to predation by birds than birds were subject to predation by birds.
Why is that?
> If you are big and cannot hide your nest very well, as well as being
> somewhat limited in your terrestrial agility,
What makes you think that pterosaurs were particularly limited in their
terrestrial agility? I've not seen any evidence of that in either their
skeletons or their trackways.
> you would want to distance
> yourself from predators--this is especially true if you are migratory and
> have the choice of remote/low predator density locations, e.g., geese,
> albatrosses, penguins.
Should I take this as an expression that access to remote locations
provide equal advantages to both pterosaurs and birds capable of making
the flight? I have no problem with that.
> No. I don't make such a clear distinction. Birds and pterosaurs had
> different strengths.
Thanks for the clarification. I agree.
> I think the real
> problem for pterosaurs--if small/medium species became extinct
> earlier--was their terrestrial existence--a relative ineffectiveness to
> defend/protect/hide/locate nests for their progeny on the ground.
What evidence is there for that?
> Of course I'm just guessing.
Oops. I wrote my last response above before reading your last
sentence. There's no harm in speculation. I think speculation can be a
very useful tool in conjunction with techniques to research that
speculation for purposes of modifying it or rejecting it as new
information comes to light.
> But the guess is informed by the problems
> and amazing solutions supplied by extant birds. I do feel that in an
> Olympic games of nesting, birds would win.
This is a leap of faith that I can't follow. Show me solid proof and
I'll let you lead me by the hand. This appears to me to be the essence
of your argument. Is it?
> This is not to say
> that pterosaurs did not also have amazing abilities--just that birds may
> have had the edge here.
This is not to say
that birds did not also have amazing abilities--just that pterosaurs
have had the edge here.
This is an equally valid (or invalid) statement. Note that I don't
necessarily believe either one of them. It'd be an interesting avenue
of research. If you have time to investigate it, I'd strongly encourage
you to do so.