Re: Ornithomimus had feathers and "display" winglike forelimbs

[Tim Williams <tijawi@gmail.com>]

Brad McFeeters <archosauromorph2@hotmail.com> wrote:

> I'm not 100% convinced that Ornithomimus had pennaceous feathers or 
> pennibrachia, even though the distribution and orientation of the markings on 
> the arm is suggestive of that.
> Zelenitsky et al. (2012) described the markings as evidence of "type 3 
> feathers or higher," but since there are no barbs preserved, all that can 
> really be said is that they do not
> resemble the type 2 feathers.  The morphology of the individual markings on 
> the adult Ornithomimus forearm also seems consistent with the non-pennaceous 
> type 1/EBFF display
> feathers of the new Beipiaosaurus (Xu et al. 2009), for example.  
> Beipiaosaurus is a basal maniraptoran yet has no evidence of pennaceous 
> feathers, so perhaps this is the more
> conservative interpretation on phylogenetic grounds?


A straightforward phylogenetic interpretation is somewhat complicated
by ontogeny.  Is STM31-1 (the _Beipiaosaurus_ specimen showing EBFF
feathers) fully grown?  If not, then the apparent lack of pennaceous
feathers might be due to the immaturity of the specimen.  (The
holotype of _Beipiaosaurus_ is from a subadult individual, and also
lacks pennaceous feathers).


Also, Sullivan &c's original definition of pennibrachium is "a
forelimb bearing long feathers that form a planar, wing-like surface
but are not necessarily used in aerial locomotion".  So even if the
long forelimb feathers of _Ornithomimus_ are not pennaceous or "type 3
feathers or higher", the feathered forelimb could still qualify as a
pennibrachium.






Cheers

Tim