RE: weird jurassic dinobird with very weird feathers

[Tim Williams <twilliams_alpha@hotmail.com>]

Jaime Headden wrote:


> I'm _sure_ I'm not the only one who is gonna say this, especially this early, 
> but I suspect this is what we can find if
> we were to look for an adult *Epidendrosaurus*.
>
> Quite just by looking at the gross number of large teeth, the apparent 
> phalanx of digit three as long as the mdII-2 
> phalanx, rather than shorter (and therefore possibly mdIII-2), and the 
> forward-oriented pubis, elongated and 
> shaft-like ischium which is nonetheless connected to its opposite, the very 
> short and broad-ended scapula compared
> to humerus, which lacks a large deltopectoral crest, and the short, 
> semi-lunate appearance of the coracoid, a broad
> U/V shaped furcula without a clear avian-esque quality (though it appears to 
> have a hypocleidal "nubbin"), and 
> certainly not least, the mandible aside from the dentition appears a 
> dead-ringer for that in *Scansoriopteryx*. 
> I think we might have the proof here that both Epi and Scan are juveniles and 
> that they are the same taxon. 
> Sadly, this taxon may need to be sunk. It certainly looks incredible.


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_.


The description also notes the similarities between _Epidexipteryx_ and 
oviraptorosaurs and (to a lesser extent) therizinosauroids.  The phylogenetic 
analysis fails to recover a 
Scansoriopterygidae_-Oviraptorosauria-Therizinosauroidea clade, or even an 
Oviraptorosauria-Therizinosauroidea clade (Oviraptoriformes sensu Sereno).  
This implies that the morphological characters in common between the three 
groups might be primitive for the Maniraptora.  I wonder if a larger 
phylogenetic analysis (including _Epidexipteryx_) might pull taxa like 
_Caudipteryx_, _Protarchaeopteryx_ and maybe even _Avimimus_ out of the 
Oviraptorosauria and into a more basal position inside Maniraptora...?


On a PT note, I like the definitions offered by Zhang &c:


Scansoriopterygidae = the least inclusive clade including _Epidendrosaurus_ and 
_Epidexipteryx_.

Avialae = most inclusive clade including _Vultur gryphus_ but not _Deinonychus 
antirrhopus_.

Aves = least inclusive clade including _Archaeopteryx_ and _Vultur gryphus_.


So Avialae is a stem-based clade that excludes deinonychosaurs, and Aves is a 
node-based clade that is anchored in _Archaeopteryx_, which has been done 
before (by Senter).  I much prefer this definition of Aves (which specifically 
includes _Archaeopteryx_) rather than limiting Aves to the crown group... but I 
know others have strong opinions to the contrary, so I won't dwell on this.  ;-)


But in defining Scansoriopterygidae it might be better to use _Scansoriopteryx_ 
(rather than _Epidendrosaurus_) in the definition.  In general it's good policy 
to include the nominative genus in a definition.  For this specific case, even 
if _Scansoriopteryx_ and _Epidendrosaurus_ can be demonstrated to represent the 
same taxon (at genus or species level), the names are not objective synonyms, 
so there will always be a chance that the two are separate genera or species.  
The chance of _Scansoriopteryx_ and _Epidendrosaurus_ ending up in different 
parts of tree are probably close to zero; but it is not zero, and the 
definition should cater for this possibility, however remote.



Cheers

Tim



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