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RE: Pterosaur origins



Dave Unwin wrote-

The long awaited paper on pterosaur origins by Hone and Benton is now out in the Journal of >Systematic Palaeontology. Hone and Benton reanalyse and reject the conclusions of Bennett 1996 >and Peters 2000, and go with the current orthodoxy that pterosaurs are 'derived archosaurs' by >which I suppose they mean ornithodirans.

Very disappointing paper.

Basically, they say Bennett's rationale for excluding hindlimb characters (which ended up dropping support for Ornithodira) was unwarranted, which is true enough. Yet this only takes two paragraphs to show and no more interesting tests (excluding hindlimb characters from other archosauromorph analyses, excluding other regions' characters, examining the homology of ornithodiran hindlimb synapomorphies) are run.

Peters' analyses get more detailed treatment, but no methodical reanalysis. They note some basic problems (unjustified exclusion of characters; characters coded differently in each analysis; Cosesaurus and Eudimorphodon treated as bipeds; outgroup issues; use of Eudimorphodon and Longisquama), but there are few critiques of specific character codings. The exception is their two paragraphs on Sharovipteryx, in which they list several characters which Peters coded that cannot be coded in the actual specimen. They then note Peters' identified Sharovipteryx arm is actually a series of ribs and that "the true arms of Sharovipteryx have now been found buried in the matrix (R. Reisz, pers. comm., 2003) and this confirms that Peters? (2000) supposed arm was incorrectly identified." Hilarious. Still, there are no data given showing how correcting these codings affects Sharivopteryx's or pterosaurs' position. An explicit list of incorrectly coded characters would have been more useful, and/or a corrected reanalysis of Peters' three trees.

The conclusions are particularly unjustified. "The results of the re-analyses of the supermatrix suggest that the Prolacertiformes should be considered the sister group to the Archosauria." And yet, no supermatrix was presented, nor was any previously published matrix reran. "The Pterosauria are not closely related to the Prolacertiformes and should instead remain among the Archosauria and probably among the derived archosaurs." Yet this has yet to be tested. Peters' analyses were flawed, but that doesn't mean a better analysis including varied prolacertiforms and archosaurs would necessarily result in archosaurian pterosaurs. "Removal of hindlimb characters has no significant effect on their position and so cannot be used as an argument for convergence and non-homology between the dinosauromorphs and pterosaurs." But, but, it did. Hone and Benton never found that exclusion of hindlimb characters left pterosaurs as archosaurs.

In conclusion, this is a good outline of a paper. It presents some valid issues but never goes further to explicitly detail most of the problems or test the hypotheses.

I should also note Renesto and Binelli's (2006) analysis suffers from the opposite problem most do. While most analyses analyzing pterosaurs' position exclude prolacertiforms, drepanosaurs and Longisquama (or just have Prolacertiformes as an OTU), Renesto and Binelli's exclude proposed archosaur relatives of pterosaurs. The only included archosaurs are Ornithosuchus, Archaeopteryx and Sinosauropteryx. A useful test would include Scleromochlus, Lagerpeton, Marasuchus and such as well. Renesto and Binelli's matrix is also quite small, only including one proximal tarsal character, for instance. There has yet to be a published matrix usefully testing pterosaurs' phylogenetic position among archosauromorphs.

Mickey Mortimer