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Re: Sobral and Langer 2008 (was pteros have lift-off)
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.
> 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?
> 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.)
> 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. 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. 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
> 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_.
> 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
(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.
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.