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Re: Steadman's review of Mesozoic Birds






From: "David Marjanovic" <david.marjanovic@gmx.at>
Reply-To: david.marjanovic@gmx.at
To: "DML" <dinosaur@usc.edu>
Subject: Re: Steadman's review of Mesozoic Birds
Date: Sat, 31 Jan 2004 14:12:42 +0100

> As for the viability of the thecodont hypothesis...I do not not think it
> viable, that much is obvious, but there is enough data to suggest that
> perhaps, in some strange twist, it could be correct, and our understanding
> on the origin of birds and their evolution can only grow through continued
> debate on that very topic.


It should be mentioned that a) "Thecodontia", the group which included all
archosaurs sensu lato ( = archosauriforms) except crocodiles, pterosaurs and
dinosaurs, has been dissolved, because cladistics has discovered its
phylogeny (about which nobody seemed to care before -- a rhizome taxon was
just too convenient); b) neither *Longisquama* nor *Megalancosaurus* nor
*Cosesaurus* are archosauriforms, and none of them has thecodont dentition.
*Cosesaurus* is most probably a prolacertiform (and thus part of the
sistergroup of Archosauriformes); *Megalancosaurus* is not even a
crown-group diapsid (!); and *Longisquama* seems to be either a
prolacertiform or to be related with *Megalancosaurus* (and the rest of
Drepanosauridae, and Weigeltisauridae).



We are all well aware of the dissolution of Thecodontia in the past 20 years or so.


> If the theropod hypothesis is allowed to reign
> triumphant without challenge it ceases to be science and becomes precisely
> what Feduccia at his worst as called it, simple dogma.


I wouldn't say so. The theory of evolution does reign triumphant (no
scientist has challenged it in the last 130 years or so), and it's still
science.
It goes without saying that "the theropod hypothesis" is actually a
plural. Which theropods (OK, which derived coelurosaurs) are the closest
relatives of birds? Dromaeosaurs? Dromaeosaurs + troodontids? Just
troodontids? Or even oviraptorosaurs + segnosaurs? Do we need the frameshift
hypothesis, or not?


> Indeed, revisions to the theropod origin of birds have
> arisen via the challenges presented to that hypothesis,

I'm having a little blackout... could you remind me of such a revision?


I was under the impression that the criticism that the semilunate carpal element was not homologous between theropods and birds, largely prompted a revision of Ostrom's interpretation of this structure, display that it is in fact a distal carpal in both theropods and birds, therefore rendering them homologous.


> Prum's 2002 and 2003 articles in The Auk bother for me
> one principal reason, they propose [...] that ornithologists
> are just too ignorant of paleontology to know the difference
> between hollow rhetoric and real science.

That Feduccia and Martin and Olson are just too ignorant of nonavian
dinosaurs to know the difference between hollow rhetoric and real science,
you mean.


Feduccia, Martin, and Olson are too ignorant of non-avian dinosaurs, indeed, but they are not bungline idiots. All of them have done important and incisive paleornithological research in their careers.


JGK

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