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RE: weird jurassic dinobird with very weird feathers



Tim Williams wrote:

<For _Epidexipteryx_ to be a 'grown-up' version of 
_Epidendrosaurus_/_Scansoriopteryx_ would require a profound ontogenetic change 
in the development of the tail.  As the authors mention in the Diagnosis of 
_Epidexipteryx_: "tail 70% of trunk length in _Epidexipteryx_, compared to more 
than 300% in _Epidendrosaurus_; 16 caudal vertebrae in _Epidexipteryx_, 
compared to over 40 in _Epidendrosaurus_; caudal prezygapophyses reduced in 
_Epidexipteryx_ but significantly elongated in _Epidendrosaurus_."  In short 
(pun intended), the length and morphology of the tail appears to be enough to 
distinguish Epidendrosaurus_/_Scansoriopteryx_ from _Epidexipteryx_.>

  I actually don't think the tail length is appropriately calculated, since it 
appears there are disarticulated proximal caudals (about 4), which are 
separated by an articulated distal accumulation of 6 or so caudals from which 
arise the "ribbons". I would suspect the tail length to have been assumed by 
the authors to be based soley on the preserved caudals, but based on Epi and 
Scans, this would arguably be a case for disarticulation and a missing segment 
of tail. My first impression was that the body and tail are on different 
sections of a slab that was reassociated, but this is reaching. As in 
*Beipiaosaurus*, I merely think the tail is disarticulated and missing about 
10-15 segments. This does not allow the animal to have the hyper-shortened tail 
of avians.

  Incidentally, I agree with Keesey and others that Aves should be limited to 
the crown, and not use *Archaeopteryx* as a specifier. This is a historical 
referent for the origin of Aves, but there is no reason to assume it MUST be a 
part of the classic living groups. This is even more important because several 
of the "avian" features of *Archaeopteryx* have been slowly whittling away, 
from the absence of a reversed hallux, apparent absence of tertial feathers, 
absence of a strongly reflexed coracoid, no apparent ossified sternum and no 
apparent reason it was capable of supporting large pectoral flight musculature, 
and thus no reason to assume Archie was capable of any form as guaranteed 
powered flight. Many of the skeletal features are in fact known in 
dromaeosaurids and oviraptorosaurs, so it might be best to restrict Aves to the 
crown and not to use *Archaeopteryx* as a specifier. I am not 100% on this 
conclusion, but right now, Archie is loosing that
 "birdy" thing it used to have to argue for it as an "avian."

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)