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Re: Sobral and Langer 2008 (was pteros have lift-off)

On Jan 22, 2009, at 6:40 PM, Tim Williams wrote:

David Peters wrote:

Sobral, G. and Langer, M. 2008 JVP 28: supplement to (3):
145A A supertree approach to prolacertiform phylogeny

Thanks. However, I can only re-iterate David M.'s message that supertrees do not contain any new data. They pool together pre- existing trees.

Understood, and yes indeed.

No taxon appears suddenly in the fossil record!

Sure they do. It happens all the time. How many basal bats (chiropterans) do we know of, for example?

We know of several basal bats. I'm sure you're asking, what came before them? I've done the comparative studies, so I know the best candidates in bats and pterosaurs, which I've mentioned before on the list and elsewhere. As in any taxa, when you include the right candidates, the mystery becomes less of a mystery. All anyone has to do is look. And not a priori exclude.

There are always clues to ancestry.

I agree. But in the absence of basal forms, these clues often arise indirectly - such as by examining the character states that derived members of a clade share with members of other clades. This is what we're forced to do with pterosaurs. (And bats as well.)

Actually, no. The literature listed in the previous post pretty much nails it. When pterosaurs are given the opportunity to nest with certain non-dino, non-archosaur, non-archosauromorph taxa --- they do. And anyone can repeat the experiment. Anyone.

That's a very bad
sign when the 'preferred' cladogram can't nail
down a sister taxon.

It does indeed give us a sister taxon. Pterosauria (or a _Scleromochlus_ + Pterosauria clade) comes up as the sister taxon to Dinosauromorpha.

Only when fenestrasaurs are EXcluded. Senter is the exception, but he made several mistakes.

A cladogram will always provide a sister taxon (more than one in the case of a polytomy). The issue here is the degree to which the recovered sister taxon helps elucidate the ancestral morphology or ecology of pterosaurs. So far, it hasn't helped a great deal.

To the contrary! That list of characters I provided earlier can be found in basal pteros, but also in various fenestrasaurs. And some surprises are coming up. Watch the skies.

But that's not the fault of cladistics, or of Hone and Benton; it's the fault of the fossil record, which hasn't yet yielded basal pterosaurs.

To the contrary!

Yes! Tim, good work!
If you're referring to Pteromimus, it is indeed related
to pterosaurs. It's a langobardisaur The first one
recorded for North America, but cladistically its
pre-Cosesaurus but it shows they too had an antorbital
fenestra. Very important.

If Procoelosaurus is also on your Tecovas list, it's a
basal croc. Both interesting specimens.

Yes, I was referring to 'Pteromimus' and 'Procoelosaurus'. Interesting stuff regarding their respective affinities - though I look forward to something on this in the published literature. From what you say of _Pteromimus_, I wonder how much material potentially overlaps with _Protoavis_.

Good question. The literature mentions cervicals that were drepanosaur-ish. Pteromimus had long cervicals of a different morphology, more like Tanytrachelos and Langobardisaurus, which are sister taxa).

Yes, you're right, but let's take it up a notch.
Forelimb length is about 100% of the hindlimb length in
Archaeopteryx. i'm still wondering, what is the
explanation for such an extension on this taxon -- or any
pre-Archaeopteryx taxon -- with such elongated forelimbs,
non-supinating/pronating antebrachia and trenchant manual
unguals if not for arboreality?

Two other alternatives:

(1) Prey capture. Longer forelimbs allowed increased reach. Targeting large prey that was grasped with both hands allowed a decrease in supination/pronation.

(2) Gliding (or some other form of non-powered aerial locomotion). Longer forelimbs allowed a larger flight surface, and the arms were used for climbing vegetation. This is partly concordant with your scenario.

Good thoughts. Scott Hartmann also had some good thoughts. I like them all.

I'm not necessarily advocating either of these scenarios. I'm only saying that alternate hypotheses to arboreality/brachiation do exist as an explanation for further forelimb elongation in the line leading to birds.

That's what I needed to know. Thank you! Good stuff.




David Peters davidpeters@att.net