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RE: Eosinopteryx, new paravian from China

How short are the arms?
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Tim Williams 
Sent: Wednesday, January 23, 2013 9:27 PM
To: dinosaur@usc.edu
Subject: Re: Eosinopteryx, new paravian from China

Gregory S. Paul  <GSP1954@aol.com> wrote:

> I cannot overemphasize, having examined a whole bunch of claws, that using
> the bony unguals to estimate the curvature of the living claw is extremely
> unreliable, and definitely will often give errant results, and should never,
> ever be done. I can also tell, just looking at the keratin sheath of the
> Eosinopterx claws, that they are very straight, and unless something is very
> wrong with the specimen they are much more indicative of terrestrial than
> arboreal habits. This makes sense considering the short arms.

Proximodistally decreasing pedal phalanges, straight claws, and short
arms are certainly *consistent* with terrestrial habits.

However, the opposite is not always true regarding arboreal habits.
It does not necessarily follow that having proximodistally increasing
pedal phalanges (especially longer ungual-bearing phalanges), recurved
claws, and long arms indicate arboreal habits.

It is extremely tricky sorting small non-avialan maniraptorans into
"arboreal" or "terrestrial" simply based on postcranial characters
such as phalangeal proportions, claw curvature (by whatever metric),
or intermembral indices.  This is especially problematic when it comes
to predatory taxa.  Characters that are *assumed* by some people to be
"arboreal" characters might just as equally be used for grasping or
immobilizing prey.  It's interesting that many of the "arboreal"
characters ascribed to _Microraptor_ also pop up in _Deinonychus_.

Some exaptation might be at play here... but that's a whole other can of worms.