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Fwd: Senter 2006, Confuciusornis, and humeral mobility
>>> Thank you, Eike, for encouraging me to read Senter's 2006 paper on flapping
>>> flight. I had never gotten around to it before:
>>> I'm curious what everyone on DML makes of it. It gives some good
>>> measurements, but leaves some out also. I would bet that Mei's furcula is
>>> about the same measurements as Confuciusornis, and I have examined those
>>> glenoids very carefully. I believe they faced laterally. They are also
>>> nearly identical to the type of Microraptor gui.
>>> The paper makes two assumptions that I question:
>>> 1) the glenoid and scapula of extinct taxa must have the same
>>> configuration as in volant neornithines in order for the humerus to be
>>> raised above the dorsum.
>>> 2) the humerus must be raised to 90 degrees above horizontal during the
>>> recovery stroke in order for flapping flight to be effective.
>>> I don't see why 1 must be true. There must have been transitional phases
>>> leading from the anteroventral glenoid of lower theropods to the lateral
>>> one of birds, and very subtle changes, maybe even just longer ligaments,
>>> could effect greater mobility in the humerus.
>>> But I'm especially skeptical of assumption 2, not qualitatively but
>>> quantitatively. Consider the paper by Sokoloff et al. (The function of the
>>> supracoracoideus muscle during takeoff in the European Starling (Sturnus
>>> vulgaris). New Perspectives on the origin and early evolution of birds,
>>> Gauthier, 1999.)
>>> In their experiments they surgically destroyed the supracoracoideus muscles
>>> of test subject starlings, then filmed them taking off and flying. The
>>> starlings' normal range of humeral motion during the recovery stroke was 90
>>> degrees above horizontal. After surgery, this range was reduced to just 50
>>> degrees above dorsal. Yet the birds could still take off perfectly well
>>> from the ground and fly just slightly less well than normal.
>>> Again, modern birds have superlative aerodynamic capabilities and highly
>>> derived anatomies. They also have a wide safety margin built in. In many
>>> cases the basic functions of powered flight may be possible with far less
>>> refined equipment.
>>> Any assumption that one feature or another is necessary for powered flight
>>> is a hypothesis, and it should be tested if we are to say anything
>>> meaningful about it.
Senior Principal Preparator
American Museum of Natural History
(212) 496 3544