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Re: Changyuraptor, new big microraptorine theropod from Early Cretaceous of China



Mike Habib <biologyinmotion@gmail.com> wrote:

> We don't exclude other functions in the manuscript. Rather, the focus is on 
> the performance effects the feathers would have related to aerial locomotion 
> (sustained or not). These effects occur regardless of the selective landscape 
> of
> the feathers. Since some of the performance outcomes are potentially 
> advantageous (control of pitch, for example) we felt that referring to these 
> as likely aerodynamic functions was warranted. Display-related or not, they 
> will still
> produce fluid forces. Furthermore, the allometry of the feathers and tail 
> length relative to body size is consistent with a pitch control hypothesis. 
> This does not exclude display as an additional (or even primary) function.


With regard to the 'selective landscape' behind the control and
stabilization conferred by the aerodynamic plumage.... The study does
make mention of it being possibly "critical to a safe landing or
precise attack on prey."  I think this is important.  First and
foremost, dromaeosaurids were predators.  The idea of dynamic leaping
and attacking goes back to John Ostrom's pioneering work on
_Deinonychus_ in the 1960's and 70's, with the suggestion that the
stiffened tail served as a "dynamic stabilizer".  IMHO it might make
more sense to put the inferred aerodynamic abilities of dromaeosaurids
into a predatory context.  An arboreal context (such as descents from
trees, or WAIR-style running up trunks) is much harder to argue for
_Chiangyuraptor_ than it is for the much smaller _Microraptor_.


Thus, it's even possible that predatory paravians like _Deinonychus_,
_Velociraptor_ and _Yixianosaurus_ were "four-winged", complete with
aerodynamic hindwings ("trousers") as well as rectrices ("tail fan")
as in _Chiangyuraptor_.  _Yixianosaurus_ had large forelimb feathers,
and _Velociraptor_ at least had quill knobs.


Returning to _Chiangyuraptor_, the apparent absence of metatarsal I
and its attached digit (hallux) is odd.  Rather than the absence being
preservational, it might be real - especially since both feet are
preserved and articulated.  Loss of the first toe is typical of highly
cursorial theropods - but the hindlimb proportions of _Chiangyuraptor_
certainly aren't those of an ornithomimid-esque speedster.  According
to the description, the second toe of _Chiangyuraptor_ lacked the
raptorial specializations typical of dromaeosaurids, so loss of the
first toe might somehow be connected with that (especially if the
first toe served a predatory function in grasping large prey, as
suggested by some studies on dromaeosaurids).  Secondary loss of the
foot's prey-grasping function might have led to the complete loss of
the first toe in _Chiangyuraptor_, rather than it simply being
secondarily shortened or elevated on the foot.  In any case, loss of
the first toe (if real) would be highly unusual for an arboreal
theropod.







Cheers
Tim