[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Steadman's review of Mesozoic Birds

John Pourtless wrote-

> I agree that the vast majority of work by adherents of various thecodont
> hypotheses is rather poor, but I feel it poor from lack of factuality, not
> from some inherent flaw in the methodology or philosophy behind it.

I assume you've read Padian (2001) and Padian and Dyke (2001) from the
Ostrom Symposium volume on the methodological and philosophical flaws behind
ABSRD.  If so, I really don't have anything to add.

> As for the paleognaths...the neotenic nature of the paleognathous palate
> been known since de Beer's 1956 work, and the case for the polyphyly of
> paleognaths was considerably bolstered by Houde's 1988 work on
> Lithornithiformes.  The molecular data, is at best problematic.  While
> molecular systematics has some utility in ornithology, it appears to
> primarily reside at the subordinal level, as indicated by some glaring
> defecsts in commonly accepted molecular phylogenies (e.g., Sibley &
> Ahlquist's "tapestry").  The morphological data suggesting that
> is holophyletic, is equally dubious.  Time and again we see characters
> advanced as synapomorphies of this assemblage to be plesiomorphic or
> neotenic.  For instance, Cracraft & Clarke's (2000, IIRC) six "unambiguous
> synapomorphies" of Paleognathae, present just this sort of problem.  There
> just seems to be irreconcilable problems with the view that Paleognathae
> represents a clade.  The cautious route might be to draw an agnostic
> conclusion, but I feel the data supports the modernist consensus reached
> Wetmore and his colleagues in the latter half of the 20th Century, that
> Paleognathae is a) polyphyletic, and b) secondarily derived from within
> Neognathae.

Well, I don't actually know enough about paleognaths to argue specific
points (my knowledge sort of peters out around Ornithurae), but I do have a
couple observations-
1. Houde's work is fifteen years old.  Not that it's age means it's wrong,
but anything from 1988 is not going to impress me as being what "the data
supports" currently.  And though I've not read Houde's book (it's at the
library, I should sometime), I find it probable Livezey and Zusi's huge
analysis of many characters and taxa is going to convince me more than
Houde's most probably much smaller selection of taxa and characters.  But my
coelurosaur analysis had different results before it included forelimb and
pelvic data, so maybe Livezey and Zusi's will have a polyphyletic
Paleognathae once it's complete.  And of course to be truly "convinced", I'd
have to examine the characters and codings myself, which could always be
flawed in some way.  Still, many characters and taxa are better than a few,
and more recent work can incorporate more and better data.
2. Though there are undoubtedly problems with molecular analyses, I would
find it odd that the vast majority (all?) have found monophyletic
paleognaths (even if they are closer to most neoavians than the latter are
to passeriforms in some, or they are the sister taxon of Galloanseres in
others) if the clade were really polyphyletic.  After all, these different
genes are all virtually independent datasets.  Doesn't their congruence mean
something to you?

Mickey Mortimer