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Re: Sinocalliopteryx (Theropoda: Compsognathidae) ate confuciusornithids and dromaeosaurids

Mickey Mortimer <mickey_mortimer111@msn.com> wrote:

> But but... surely O'Connor et al. (2011) showed it's most reasonable to 
> conclude associated arboreal birds in a theropod's stomach mean the theropod 
> is probably
> arboreal.  Arboreal Sinocalliopteryx, here we come!

It's still possible that _Microraptor_ hunted in an arboreal habitat.
This doesn't necessarily make it arboreal.  If _Microraptor_ spent
most of its time on the ground, yet opportunistically ventured into
trees to snatch arboreal prey (like roosting birds), then it wasn't
actually arboreal: it was a terrestrial predator that occasionally
climbed trees.

(quoting Xing et al.):

> Confuciusornis was not as well adapted to perching as enantiornithine birds, 
> but does nonetheless
> possess long curved pedal claws and a posteriorly-facing hallux, and was 
> capable of powered flight.

According to at least two studies, _Confuciusornis_ might *not* have
been capable of powered flight:

Senter, P. (2006) Scapular orientation in theropods and basal birds,
and the origin of flapping flight. Acta Palaeontologica Polonica:

Nudds, R.L. and Dyke, G.J. (2010) Narrow primary feather rachises in
_Confuciusornis_ and _Archaeopteryx_ suggest poor flight ability.
Science 328: 887-889.

I doubt if either of these studies are the last word on the topic.
However, the assumption that basal (non-ornithothoracean) avialans
were capable of powered flight is on very thin ice.  Not just because
of the conclusions of the above two studies, but also the inferred
absence of an elevating supracoracoideus.  In any case, it is highly
unlikely that confuciusornithids (and other basal avialans) were
capable of a ground-level take-off.  So they needed to climb trees in
order to gain elevation.  It might have been at this point that these
avialans were most vulnerable to predation.

The pes of confuciusornithids suggests that they divided their time
between trees and the ground (although the hallux of _Changchengornis_
appears to be better adapted for perching than that of
_Confuciusornis_).  By contrast, the enantiornithean found in the
tummy of a  _Microraptor_ was specialized for arboreality.  Also,
_Microraptor_ was better adapted for trunk-climbing than
_Sinocalliopteryx_ - for more reasons that simply being much smaller
and having proportionally much longer arms.  So paleobiologically
speaking, _Microraptor_ preying upon an enantiornithean is not quite
the same as _Sinocalliopteryx_ preying upon a confuciusornithid.

> Avian prey is known to constitute nearly half the diet of some leopard cats 
> (_Prionailurus bengalensis_) [60],
>  which both climb trees to prey on roosting birds and ambush foraging birds 
> on the ground."

To me, this is the best analog for the behavior of _Microraptor_.  The
time-honored cursorial-vs-arboreal dichotomy is not just inappropriate
when it comes to the origin of flight, but also unnecessarily
constraining when it comes to reconstructing the behaviors of small
basal paravians and avialans - especially microraptorines,
archaeopterygids, jeholornithids, and confuciusornithids.  Climbing up
trunks, and parachuting or gliding back down to earth, seems to gel
best with the morphologies (both the integument and the skeleton) of
these taxa.