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Re: More on Argentavis



Evelyn Sobielski wrote:

Problem is that basically each dataset provides a
different tree. Even different sequence-based trees
don'tr eally agree well. Also, fossil evidence beats
inference from any kind of data hands-down. It's rare
that a fossil say "ain't so", but if it does, that's
that.

Ah, but that's not really fair, is it? ;-) Let's say that you argue that loss of flight occurred more than once in ratites; but I argue that loss of flight only evolved once in ratites (in the most recent common ancestor of all extant ratites).


If you find a fossil ratite that was volant, then you are right and I am wrong. My hypothesis is refuted by the discovery of a ratite that shows characters consistent with flight.

But if we do NOT find any volant ratites, and fossil flightless ratites keep on piling up, then you can still argue that your hypothesis has not yet been refuted. You could claim that fossil volant ratites existed, and we just haven't found them yet.

In short, the "absence of evidence is not evidence of absence" argument works in your favor, but not in mine.

The morphology-based phylogenetic analyses tend to support a single origin of flightlessness in ratites (though the spotty fossil record for ratites doesn't help). But I agree that Cooper &c's mitochondrial phylogeny is not the final word on the matter. Still, it can't be ignored, and it does seem to agree with the morphological evidence.

Any hypothesis must deal with _Palaeotis_ and possibly
_Remiornis_, the lithornithids, etc (even if not
ratites, they're too close for comfort).

I don't see how these make any difference at all. AFAIK, _Palaeotis_ and _Remiornis_ were both flightless. As such, if they are ratites (i.e., within the crown-group) they have no impact on the question of how many times ratites lost flight - except to demonstrate that ratites were flightless as far back as the early Palaeogene.


As for the lithornithids, they were flighted, but even if they are within crown-group Palaeognathae, they are almost certainly outside the ratite crown-group.

Ideally, it
must also find a place for _Limenavis_

Why? _Limenavis_ is not even within the Neornithes crown group. It has no effect whatsoever on the issue of flightlessness in ratites.


and deal with
assorted touch-me-nots like  USNM 336103, _Wyleyia_,
_Paleocursonis_, etc (the latter may be easy as it
could just as well be non-avian).

USNM 336103 is the "Green River Palaeognath". I don't know much about this one, but unless it's a volant palaeognath AND within the ratite crown-group, it's a red herring. As for _Wyleyia_ and _Palaeocursornis_... you're really drawing a long bow there.


Yes, these are the guys I thought of (+ _Leipoa
gallinacea_

I'd forgotten about _Leipoa gallinacea_ (formerly _Progura_), the giant extinct malleefowl from Australia. Thanks for the reminder.


It seems to boil down to what evolved faster:
wing reduction or size increase.

Yep, good point.

In any case, in _L. gallinacea_, _Megavitiornis_ and
_Sylviornis_ we have evolution towards giant size and
flightlessness on large to largish landmasses

Australia is certainly BIG. New Caledonia is decently sized. But Fiji ??!!

Cheers

Tim

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