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Re: Sharovipteryx an ornithodiran??



David Peters (davidrpeters@earthlink.net) wrote:

<Sure finger V of pteros is tiny, but that goes back to Macrocnemus. In fact
the relationship of IV to V is always much greater in every member of the
Macrocnemus > pterosaur clade than in any archosauriform.>

  I would like to remind debators that in this case, one must use evidence that
can be verified or has been verified in making one's arguments or corollaries.
The technique Dave has used to reconstruct ptrerosaurs, pterosaur ancestors,
and his subsequent phylogeny, has been questioned without a clear modus
presented on precisely using the technique used to do so. Thus we should
attempt to corroborate our data without it until it is proven.

  Similarly, arguing about "pterosauromorphs" being crocs from an abstract is
not the same as examining the material, or at least reading the dissertation
itself, which I highly recommend.

  Statements requiring at least some amounts of assumption, such as "that goes
back to Macrocnemus", in that it implies a relationship of direct comparisons,
should be elaborated if they are to be held in contention to the prevailing
theory, which does not support prolacertiforms in this case as pterosaur allies
(not that it really supports anything else right now save for a few large
cladistic analyses which have been verified and some general phyletic
comparisons).

  Anyways, I have not much to say on the matter of *Sharovipteryx*, given how
poorly it is poreserved, the difficulty of discerning much of anything about
the region anterior to the shoulders, and the details of the skull at all. The
arms are incomplete, and I do not agree with Dave's interpretation of long
arms, given the remains are also partially disarticulated and thus,
untrustworthy regarding consistency of form. In *Scleromochlus*, I have said
plenty before, and I largely agree with Benton in placing it close to the
archosaur root, but like Dave, I do also see a lot of croc-like features.
Unlike Dave, I caution myself that many of these seem plesiomorphic, and would
exist even in basal dinosauriforms deriving from a croc-like basal archosaur
which gave rise to both crocs and dinosaurs. When looking at taxa closer to
dinosaurs than *Scleromochlus* has been proposed to, we see many of these same
features. In fact, *Scleromochlus* shows them in even further reduced form, and
appears to be more dinosaurian in the structure of its pes, metatarsal
arrangement, fifth toe, and proximal tarsals, than does even *Lagerpeton* or
*Marasuchus*. That said, there are also some crocs, such as the possibly
paraphyletic grade of taxa called "sphenosuchians", that have developed some of
these features as well, and we should be concerned over how we interpret
possible convergences. And that goes for anyone proposing a feature is
indicative of some phylogenetic lineage or another, any lineage, and any
researcher. Convergences happen, deal with it.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)

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