[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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.
>>> 
>> 
> 

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544