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Re: Campbell's even crazier than a MANIAC? (archeopteryx
It IS easier to become airborne from an elevated position and you
can also travel much further. Even if theropod could jump really
high, it would still only be falling from a few feet, which would
only give it a tiny fraction of the air time it would get from
jumping out of a 50 foot tree. Plus after jumping it would
immediately begin to slow down, and in the end it would have been
better off simply running.
Ah, and it returns. This came up in another recent discussion, which
sadly became rather more heated than it ought to have been. In any
case, I suggest being careful with the term "easy" in this context.
It does, indeed, take less power to drop from a height (assuming you
are already there), than to leap from a substrate. However, what is
"easy" in terms of biological systems depends entirely on the
ancestral state. Birds inherited highly powerful hindlimbs from their
ancestors, which were mechanically capable of powering leaping
launches. This doesn't mean that the origin of flight in birds was
purely cursorial in nature, but it does indicate that an arboreal
stage isn't mechanically required.
Incidentally, the airspeed in leaping launches is generated from the
leap, not a subsequent fall from the top of the jump. It is also
worth noting that arboreal birds tend to launch by leaping from the
elevated substrate, so arboreal launches are probably only rarely
simple "falls". There is also the issue of the phylogenetic timing of
the power stroke versus the timing and pace of airfoil evolution - a
great deal depends on how these features map relative to each other in
No, the intermediary stage proceeding flight DOES NOT have to be
gliding. It might have been; but this cannot be assumed.
I think it does, simply because there has to be a transition between
a simple fall and powered flight, and gliding is much less energy
consuming than flapping your wings to achieve what is basically a
prolonged fall. Yes I guess an animal could flap its wings to
prolong its fall, but why waste the energy when it could achieve the
same thing by evolving a larger wing surface to simply glide.
A fall to flapping transition is only one of the possible array of
transitions. What consumes the most energy is actually rather
complicated, since the climbing costs have to be included, but in any
case, biological transitions don't always follow a low-energy path.
The flapping stroke might have evolved secondary to airfoil expansion,
but it also could precede airfoil expansion or evolve in synchrony.
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205