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RE: Alvarezsaur spurs (was Re: dino-lice)

If the feathers were vibrating with some force, perhaps they were used for 
acoustic communication instead of or in addition to visual display.  

> Date: Wed, 20 Apr 2011 09:54:28 -0400
> From: jaseb@amnh.org
> To: tijawi@gmail.com
> CC: dinosaur@usc.edu
> Subject: Re: Alvarezsaur spurs (was Re: dino-lice)
> My favorite interpretation of alvarezsaur pectoral limbs has always been
> that they supported fans of long feathers or ribbon- like keratinous
> straps (like ETFs in scansoriopterygids) for display. In figure 18 of the
> Patagonykus monograph (Novas, F. E. 1997. Anatomy of Patagonykus puertai
> (Theropoda, Avialae, Alvarezsauridae), from the Late Cretaceous of
> Patagonia. Journal of Vertebrate Paleontology 17(1); 137-166.) there
> appears to be a lateral groove on Ph I 1 of the right manus, and the
> groove is over 40mm long. This feature, possibly combined with the ulna,
> may have served well in anchoring follicles.
> One virtue of my hypothesis is that it explains why flapping musculature
> may have hypertropied while the hand was reduced in both size and
> function. The shorter arm should have been able to flap or even vibrate at
> much higher frequencies and with some force. I picture the feather fan
> trembling not unlike the rectrical fan of the peacock. Another virtue of
> this hypothesis is that it is consistent with archosaur biology in that
> birds have arrived at a diversity of bizarre morphological adaptations for
> display, while none that I know of have been highly modified for digging.
> The problems include that the arm morphology doesn't really suggest a way
> to fold such a fan for fast running, and that the hands are not clearly
> modified for strong feather attachment with lateral flanges. But it is
> possible that the follicles lay in a soft tissue "remigial bulb".