Monday, February 15, 2010

Pterosaur Relationships

Pterosaurs on a theropod blog?!  What has the world come to?  Well, a consequence of having a blog based on material for my website and projects is that when I'm too busy to work on them, the post count lightens.  But I had some thoughts based on a recent DML message that's been repeated numerous times in the past.  It concerns the sister taxon to Pterosauria.  In the literature, we find two hypotheses- David Peters thinks they're related to protorosaurs within Lepidosauromorpha; everyone else thinks they're related to dinosauromorphs within Archosauromorpha.  Now it would be easy enough to just say Peters is a fringe researcher and that we should go with the professional consensus view.  But I don't believe that's justified here.  Certainly Peters has methodological problems.  His Photoshop method has been shown to fail multiple times (Bennett, 2005) and I don't believe half the things he sees are real.  Plus he doesn't understand how to perform a phylogenetic analysis correctly in multiple respects.  So do I trust his analyses?  Absolutely not.  But does that mean he's wrong?  No.  The ironic thing, and the point of this post, is that the other side is almost as bad.  Oh sure they (probably) make less anatomical errors and have a better understanding of correlation and ordering for characters, but their matrices are flawed in other ways.  Bennett (1996) had Lepidosauromorpha and Prolacertiformes (now recognized as polyphyletic) as OTUs, and the former was the outgroup.  Sereno's (1990, 1991) "analyses" never include conflicting data so are demonstrations of hypotheses instead of tests.  Benton (1999) only included archosauriforms.  Hone and Bennett's (2008) supermatrix method oddly included both lower level taxa (e.g. Squamates, Champsosaurus) AND the higher level taxa they belong to (e.g. Lepidosauromorpha, Choristodera), but even stranger these taxa did not group with themselves, showing the matrix is highly flawed.  One obvious way is actually the exact thing I complained about earlier on this blog- many taxa are only coded for a small percentage of characters.  What good are 324 characters if Dinosauria is only coded for 90 of them, or Lepidosauromorpha for 78 of them?  Thus no published study is a useful test of pterosaur origins and they might as well be left as Sauria incertae sedis until someone takes the time to do an analysis properly.

4 comments:

  1. I agree.
    Italy has the oldest pterosaurs and several basal saurians and archosauromorphs: I would like to perform a large-scale phylogeny of permo-triassic saurians, in order to test ALL conflicting hypothesis about pterosaur evolution (... after publishing my theropod phylogeny).
    Senter's PhD Thesis is probably the only good analysis testing pterosaur position among Sauria because it included drepanosaurs, lepidosaurs, basal archosauromorphs/forms and basal dinosauromorphs. Its study focused on bird position among Sauropsida, and placed pterosaurs (the analysis included 2 basal forms) in Avemetatarsalia, but would be a good starting point, that could be expanded adding more basal reptiles and more characters.

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  2. I'd get rid of your photos. No need to scare people away.

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  3. "I'd get rid of your photos. No need to scare people away."

    Excellent. They'll keep all the bigots away.

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  4. David MarjanovićFebruary 20, 2010 at 9:15 AM

    I would like to perform a large-scale phylogeny of permo-triassic saurians, in order to test ALL conflicting hypothesis about pterosaur evolution

    When do you intend to publish Megamatrice? I propose a collaboration with my postdoc project which is supposed to start this fall (amniote phylogeny with emphasis on turtle origins and based on a matrix that will be so huge I'm almost scared of it myself).

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