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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".