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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 the phylogeny.


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.


Cheers,

--Mike




Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280-0181 habib@jhmi.edu