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Re: Microraptor hanqingi, new species from China.



GSPaul <GSP1954@aol.com> wrote:

> The evidence that S. zhaoianus is fully arboreal is so strong it is a tad
> dull.


_Microraptor zhaoianus_, you mean.  In DA, you argue quite forcefully
that _Microraptor_ and _Sinornithosaurus_ were specialized arboreal
climbers.  IMHO, the features marshaled in support of arboreality are
hardly compelling.


For example, having long and slender limbs is not necessarily an
arboreal trait; and comparing these maniraptorans to long-limbed
primates, such as spider monkeys, is drawing an anatomical long bow.
Primates have a completely different osteology to that of dinosaurs,
and are blessed with hands and feet that are consummately adapted for
grasping, and extensive mobility at all their joints.


Other characters cited in support of branch-grasping in _Microraptor_
and _Sinornithosaurus_ don't mesh with the skeletons themselves.  DA
states that the three central metatarsals (II-IV) were of the same
length; however, in both _Microraptor_ and _Sinornithosaurus_, the
third metatarsal is clearly the longest (Xu et al., 1999; Hwang et
al., 2002).


Rather than having "so many clear-cut climbing adaptations" (p.127 of
DA), the vaunted climbing adaptations in these paravians are actually
quite murky - not just discrete features, but also the various indices
(especially the phalangeal index, which comes up a lot).  Once you
drill down into the "arboreal" features attributed to _Microraptor_
etc, the connection with arboreality for most of these features is
ambiguous at best (Dececchi & Larsson, 2011; Dececchi et al., 2012).


I'm prepared to accept that some paravians were capable of climbing,
including _Microraptor_ and _Sinornithosaurus_.  Yes, the enlarged and
hyperextensible second toe could have been used as a climbing aid.
The distal migration of the hallux is certainly intriguing (although
it could just as easily be a predatory feature).  And the morphology
of the wings certainly lends itself to a parachuting/gliding function.
 But having minimal scansorial ability is a very different thing to
saying that these maniraptorans were "fully arboreal".


I know I'm having a rant against GSP's arboreal theropod paradigm
here.  It's not intended to be a personal attack - in the spirit of
free and open debate, I'm merely disputing many of the features used
by GSP and others to put _Microraptor_ and _Sinornithosaurus_ up in
the canopy.


> The situation with Archaeopteryx is much more complicated and interesting.


That's something I do agree with.  But if _Archaeopteryx_ did enter
trees, it's the kind of theropod that was clearly not comfortable in
the arboreal realm.  Same goes for any other non-ornithothoracean
theropod.  With the exception of _Epidendrosaurus_, that is.... but
that's another story.






Cheers

Tim