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Ground-up vs Trees-down... here we go again (was Re: titanosaurs )



Dinogeorge wrote:

> For one thing, most birds are a >lot< heavier than insects, which have 
> significantly different aerodynamic properties from birds. The origin of
> flight in insects cannot be closely related to the origin of flight in
> birds and is pretty much irrelevant to it. I don't know why you even 
> bring this up, except to add a straw man to your list of "flaws" in my 
> reasoning.

The origin of insect flight is certainly relevant to avian flight - insofar
as mathematical models have been constructed for both that demonstrate that
the evolution of flight is possible without the aid of gravity in producing
lift and airspeed.

> I would say that evolution >always< takes the easiest course, which is 
> determined by the raw material available. This is because the chance of 
> finding the easiest course is much greater than that of finding a 
> harder course. That, indeed, is the definition of "easiest course." 

You've either deliberately or accidentally misrepresented what I said.  From
a biomechanical standpoint, evolving flight with the assistance of gravity
is less bioenergetically expensive since the animal ("pro-avian", if you
will) does not have to exert itself as much working against gravity.  Thus
it is "easier".  However, a ground-hugging pro-avian does not baulk at
launching itself aerially from the ground because it would be "easier" to
launch itself from an elevated position.  As I said, the creature can use
what it's got; and selection can only act on that.

> In flight origins, gravitational energy is there for the taking. 

Let me make something clear: I tend to favor a hypothetical pathway in which
pro-avians used gravity to their advantage in the evolution off flight.  But
my preference is not based exclusively on what "feels right" to me, but is
based on the corpus of available evidence.

> It's ["ground-up" vs "trees-down" argument] is only considered outdated 
> by those who cannot mount a convincing argument that "ground-up" works. 

Bulldust.  Unless you can provide evidence that a non-avian maniraptoran
could not leap into the air from both the ground or a tree, then the
"ground-up" vs "trees-down" dichotomy should be regarded as an artificial
and arbitrary constraint.

That's enough from me for today.  Back to work...



Tim