RE: weird jurassic dinobird with very weird feathers

["Thomas R. Holtz, Jr." <tholtz@umd.edu>]

> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Jaime A. Headden

Let me first note: like Jaime, my thought on seeing this specimen was "so
this is what an adult _Epidendrosaurus_ looks like".

> 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.

In point of fact, had/if this paper had come to me for review, that is
something I would grill them on. They do not clearly have the end of the
tail, and yet they use this as major evidence of the distinction between it
and _Epidendrosaurus_.

>   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."

Agreed. Additionally, I think we are within a year or four of numerous
papers that might place Archie outside of Deinonychosauria + Avialae. Or
within that clade, but not on the bird branch...

Finally, I think that having pre-review papers available is a stupendously
BAD idea. A lot of details can get modified between submission and
publication as result of reviews, including: the name of the organism
(_Incisivosaurus_, _Eotyrannus_, and _Guanlong_ all went into their
respective submissions with different genus names, for instance), the
results of the phylogenetic analysis, and even the identification of the
homologies of the bones. Don't know what Nature is thinking...

One point, though: a dubious nomenclatural status is a shared derived
feature of -_Scansoriopteryx_ + the new guy!

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
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                        University of Maryland
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