Re: At long last! Turner, Makovicky & Norell on dromaeosaurids

[Tim Williams <tijawi@gmail.com>]

Jason Brougham <jaseb@amnh.org> wrote:


> Note that it has all kinds of information for those of us who study bird 
> origins. It finds no support for the phylogeny of Xu et al., 2011; it moves 
> Xiaotingia into the
> Troodontidae, and moves Archaeopteryx back into Avialae.


Having _Xiaotingia_, _Anchiornis_ and _Jinfengopteryx_ at the base of
the Troodontidae means that (unsurprisingly) basal troodontids were
the most "bird-like" troodontids, complete with long arms and a fairly
"modern" plumage.  Derived troodontids were better adapted for
cursoriality, and tended to have much shorter arms.


> Furthermore it recovers Epidendrosaurus as a basal avialan (the MOST basal 
> one, before Archaeopteryx), and places Epidexipteryx as just outside the 
> split between
> Avialae and deinonychosaurs, possibly giving us a glimpse or a model for what 
> the ancestral paravian looked like.


Only one additional step is required to put _Epidexipteryx_ in the
Oviraptorosauria; so I doubt if we'd heard the last of where
_Epidexipteryx_ belongs in the Maniraptora tree.  _Epidendrosaurus_ is
problematic because of the juvenile nature of the specimen(s).
Another unsettled taxon is _Pedopenna_, which jumps all around the
tree.


> It also recovers the most basal dromaeosaur as Mahakala, a short - armed 
> form. In this study, when we look at the most basal paravians and their 
> closest sister groups,
>  we see many forms that do not look extremely flighty (Epidexipteryx, 
> Incisivosaurus, Mahakala). This may renew the possibility that the ancestral 
> paravian did NOT
> glide or fly, nor even necessarily have long wings. Only an ancestral state 
> analysis can assess this question empirically.


_Mahakala_ was certainly not "flighty".  But it seems certain that its
short arms were secondary - as in _Caudipteryx_, _Tianyuraptor_, and
derived troodontids.  Forelimb length is highly variable among
maniraptorans, but I think there's abundant evidence that a long
forelimb was the primitive condition. for Paraves  For me the question
is: Why long forelimbs?


The postcranial skeleton of _Incisivosaurus_ is not known, so the
possibility remains that _Incisivosaurus_ may have had some aerial
locomotory ability.  _Incisivosaurus_'s closest relative,
_Protarchaeopteryx_, has very long forelimbs (forelimb feathers are
not preserved - although pennaceous feathers are preserved along the
tail).  _Protarchaeopteryx_ might have been some form of parachuter or
glider, in which case this might also be true of _Incisivosaurus_.


Recall that there are biomechamical studies which indicate that true
flapping flight did not arise until fairly late in avialan evolution -
after confuciusornithids.  According to Turner &c, the osteological
features involved in bracing the shoulder and re-directing compressive
forces first appear in forms like _Jeholornis_ and _Jixiangornis_, and
after _Archaeopteryx_ and _Sapeornis_.   I kinda wonder what these
derived pectoral characters (strut-like coracoid; ball-and-socket
scapula-coracoid; ossified sternum, etc) were used for in proto-birds
that couldn't flap...


> I look forward to a fruitful DML discussion on this pivotal piece.

Be careful what you wish for.   ;-)


Brad McFeeters <archosauromorph2@hotmail.com> wrote:

> Strangely for a paper that sets out to review all known dromaeosaurids, there 
> is no mention of *Luanchuanraptor henanensis* Lü et al. 2007.


No mention of _Hulsanpes_ either.  Still, these are minuscule quibbles
in an excellent body of work.






Cheers

Tim