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RE: for David M.: Scleromochlus ankles + Brusatte et al. supertree
David Peters wrote:
> Everyone has known for a long, long, time, pterosaurs don't quack
> like an archosaur.
Everyone except me, apparently. I thought pterosaurs can quack like an
archosaur, and (more importantly) can walk like an archosaur - especially
> To quote an esteemed expert on pterosaurs, Chris Bennett 1996 (and
> also quoted by Hone and Benton 2007): "“… few characters can be found
> that unite [pterosaurs] with any other clade among the archosaurs.“
Be aware that Bennett (1996) actually *excluded* hindlimb characters from his
analysis. Given the important role accorded to hindlimb characters in
archosaur evolution (especially those pertaining to the ankle), this might be
viewed as a little unfair.
Bennett's rationale was that hindlimb characters were associated with bipedal
digitigrade locomotion, and were therefore homoplastic between dinosaurs and
pterosaurs. Given that this was an untested *a priori* assumption, the
exclusion of hindlimb characters makes this study less esteemed than it might
otherwise have been. Moreover, it's unsurprising that "few characters" were
found to unite pterosaurs with other dinosaurs, given that many/most potential
synapomorphies were chucked out before the analysis was even run.
> To quote another esteemed expert on pterosaurs, David Unwin 2004, "
> But there are difficulties with this suggestion [that Scleromochlus
> is the closest known relative of pterosaurs] and with the more
> general idea that pterosaurs are ornithodirans."
I don't think these difficulties (should they exist) are insurmountable. Also
it's worth noting that pterosaurs can be ornithodirans without first
establishing a _Scleromochlus_-Pterosauria sister group relationship.
> Now would be a good time to listen to what Chris and David say.
It might be worth giving Kellner a hearing too, lest you be accused of
cherry-picking quotes. Says Kellner (2004):
"Assuming that the PAJ [pterosaur ankle joint] is representative of
Pterosauria, it adds support to a close relationship of this clade of volant
reptiles and Dinosauromorpha. The lack of an astragalar posterior groove and
the reduction of the calcaneal tuber (absent in Pterosauria) are some of the
features shared among members of both clades."
This is based on examination of the well-preserved ankle-joint of two
pterodactyloid species. As Kellner argues, there's no reason that this tarsal
morphology (PAJ) isn't typical of pterosaurs, including basal forms which have
ankles that conform to PAJ, although the details are often absent or poorly
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