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



On Mon, Aug 15, 2011 at 4:52 PM, Tim Williams <tijawi@gmail.com> wrote:
> Mike Keesey <keesey@gmail.com> wrote:
>
>> That's only a problem if you assume that "trees-down" is an essential
>> part of the neoflightless hypothesis.
>
> http://gspauldino.com/JVP01.pdf
>
> (Entitled: "Increasing evidence for an arboreal origin of
> dinosaur-avian flight, and for losses of flight in post-urvogel
> dinosaurs")

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.)

This makes for four possibilities:

1) Both are false. The lineage from the maniraptoran ancestor to the
avialan* ancestor does not include arboreal members (although some
offshoots may have acquired arboreality), and the acquisition of
flight in the avian lineage (i.e., the avialan* ancestor) postdates
the eumaniraptoran ancestor.

2) Both are true. Arboreality is the ancestral condition for most or
all of Maniraptora, and the acquisition of flight in the avian lineage
predates the eumaniraptoran ancestor.

3) Arboreal yes, neoflightless no. Arboreality is the ancestral
condition for most or all of Maniraptora, but the acquisition of
flight in the avian lineage postdates the eumaniraptoran ancestor.

4) Arboreal no, neoflightless yes. The lineage from the maniraptoran
ancestor to the avialan* ancestor does not include arboreal members
(although some offshoots may have acquired arboreality), and the
acquisition of flight in the avian lineage predates the eumaniraptoran
ancestor.

* apomorphy-based sense

-- 
T. Michael Keesey
http://tmkeesey.net/