RE: The Men Who Stare At New Papers

[Tim Williams <tijawi@yahoo.com>]

Responding to two posts in one...

David Marjanovic wrote:


> One obvious activity that requires firmly attached feathers is flight.
> But there are others (WAIR, stability flapping...).


Exactly.  And maybe "grappling with large prey" could be added to the list, 
especially where _Velociraptor_ is concerned.


Penguins (and apparently plotopterids too) also require firm attachment of 
remiges, for subaquatic locomotion.  However, these flightless birds have pits 
rather than nodes to help secure attachment of these feathers.


> Do any extant flightless birds have quill knobs? I think not...


Apparently some flightless birds do have quill knobs.  I've heard dodos do 
(though I'm darned if I know why).  Many flighted birds actually lack quill 
knobs.  Nevertheless, Turner et al. (2007) demonstrate that there is a 
statistically significant correlation between quill knobs and powered flight in 
modern birds.  However, all modern birds are descended from a most recent 
common ancestor that was flighted (and so presumably possessed quill knobs), so 
this correlation probably shouldn't be extended to non-avians such as 
_Velociraptor_ and _Rahonavis_ (IMHO).

Erik Boehm <erikboehm07@yahoo.com> wrote:


> I thought flight (gliding or powered) came before the
> enlarged breastbone, and that primitive birds (which clearly
> could at least glide) didn't have them?


_Archaeopteryx_ lacks an ossified sternum, but dromaeosaurs have one.  An 
enlarged sternum has been considered diagnostic for maniraptorans, although the 
sternum of non-avian maniraptorans pales in comparison with the huge, keeled 
breastbones of advanced birds.  As David puts it: That's another level of 
"enlarged".  :-)


> Unless, of course, Velociraptor had flying/gliding
> ancestors / was secondarily flightless, which appears
> likely.


So according to your logic, if _Velociraptor_ has a flight-related feature 
(such as quill nodes), it must be because it retained this feature from a 
flying ancestor.  But if it lacks a a flight-related feature (such as strongly 
bowed metacarpal III), it must be due to secondary loss, because it "appears 
likely" that _Velociraptor_ evolved from a flying ancestor.


This strikes me as circular reasoning.  To me, if a non-flighted, non-avian 
maniraptoran such as _Velociraptor has a feature that is otherwise seen only in 
birds, then it makes me wonder if that feature really evolved for flight in the 
first place.




Cheers

Tim