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



I think the point about the modified fingers is a good one, but ratites
retain the claws, of course. Hoatzins either retain or reversed back to
mobile finger joints. Ratites don't have pygostyles.

I think there'd be more anatomical support for the idea that ratites had
flying ancestors if ratites retained the large flat flanges on the first
phalanx where the primaries anchor.

We could write a scenario, and I think maybe someone (Thulborn?) has,
where ratites evolve directly from, say, ornithomimids, and neognathous
birds spun off from, say, oviraptorids much later. Ratites would still
have the three fingers, at least as embryos, and claws, and the rest could
be explained by disuse. Ratite fingers aren't highly fused nor modified to
support a rigid wing.

Also a rigidly feathered wing, or pennibrachium after Sullivan et al.
(2010), doesn't have to be used in flight.

Perhaps it is the very notion of adaptive explanations that I'm skeptical
of. I have more faith in sober surveys of the distribution of characters
rather than coming up with speculative explanations for the apparent
pattern. A lot of elegant adaptive explanations, ones that thousands and
millions of words have been written about, have been proven false by later
evidence. The idea that dinosaurs (they didn't say non-avian then) went
extinct because they were cold blooded and the world got too cool for them
is just one such doozy.

But it is fun to speculate. I do appreciate the contributions of everyone
on the DMl along these lines because the speculation is pretty fun, and
jogs the imagination.

-Jason


Dr. Ronald Orenstein wrote:

> Has anyone come up with an adaptive explanation for the degree of fusion
> and finger reduction in the avian hand (including the hand of living
> ratites) that does NOT involve supporting a more or less rigid feathered
> wing?  I suppose someone will point to alvarezsaurids, but the similarity
> does not seem very great (and I suppose they could be secondarily
> flightless too).  This is not a question of reducing forelimbs (as seen in
> tyrannosaurids), which I suppose can be explained as a consequence of a
> shift in a bipedal animal from manipulating or catching food with the hand
> to using the mouth - but of the very specific type of fusion seen in
> modern birds.  I admit this point isn't proof of anything (it might be
> characterized as an argument from incredulity) but surely it is at least
> suggestive of secondary flightlessness in ratites.  Could the same thing
> be said of the pygostyle, or could this be explained as an adaptation to
> support and manipulate a
>  display structure?
>  
> Ronald Orenstein
> 1825 Shady Creek Court
> Mississauga, ON L5L 3W2
> Canada
> ronorenstein.blogspot.com
>
>
>>________________________________
>>Jason Brougham wrote:
>>
>><But cladograms don't tell us the actual ancestors. They tell us the
>>sister groups, and if you found an actual ancestor, as improbable as
>>that is, it would show up in a cladogram as a basal sister group. So, I
>>guess, this debate is outside science. There is no rigorous or empirical
>>scientific method that can demonstrate if an animal had a flying
>>ancestor or not.>
>>


Jason Brougham
Senior Principal Preparator
Department of Exhibition
American Museum of Natural History
81st Street at Central Park West
212 496 3544
jaseb@amnh.org