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RE: weird jurassic dinobird with very weird feathers
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
Avialae = most inclusive clade including _Vultur gryphus_ but not _Deinonychus
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.
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