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Re: Ah ha! That's where therizinosaurs came from

Mike Keesey <keesey@gmail.com> wrote:

> The two clauses of the title and the two paragraphs of the abstract
> describe the arboreal hypothesis and the neoflightless hypothesis
> separately. They seem pretty independent to me. (The author confirmed
> this elsewhere in the thread, although of course he happens to support
> both of them.)

Yes, the two hypotheses are independent - although in GSP's they tend
to become entangled.  "Dinosaurs of the Air" is replete with
references to arboreal theropods, including (but not limited too)
restoring _Archaeopteryx_ as having a hoatzin-chick-like ability to
clamber quadrupedally in trees.  There was also GSP's _Prehistoric
Times_ article from 2003 ('Screaming Biplane Dromaeosaurs of the Air')
which advances small dromaeosaurs ("sinornithosaurs") as arboreal
("Sinornithosaurs can be viewed as the hawks of our time, perching in
tree waiting for something to come by...").  There is even an
accompanying illustration of a 'perching' sinornithosaur.  And as GSP
himself has said recently, "The strict neoflightless hypothesis does
not require arboreality. I think it did but that's another matter".

I don't mean to pick on GSP, because there is some evidence that
certain small maniraptorans were acquiring scansorial features.
Nevertheless, I can't help but think that the concept of perching
maniraptorans is inspired more by what came after (i.e., we know that
birds perch, so maybe perching behavior began long before birds
acquired a specialized perching foot) combined with the intuitive
attraction of the idea (perching dromies are just plain cool) rather
than hard scientific evidence.

For me, the arboreal-cursorial dichotomy is not only inappropriate in
terms of launch kinematics, but also from a broader paleobiological
perspective.  Small maniraptorans might have been quite adventurous,
and had a diet that targeted insects and plant products, irrespective
of whether these food sources were close to the ground or at the top
of a cycad or conifer.  So "arboreal" is not so much an alternative to
"cursorial", but an expansion.