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Re: pterosaur femora sprawl
If we look at birds and bats, the other volant tetrapods, both got
their wings after a bipedal phase (bats inverted).
Bats hang, sure, but I wouldn't call them bipedal. And we don't have
enough information on their ancestry (given the enormous range of
competing phylogenetic hypotheses on bat origins) to gauge what the
ancestral state was. Besides, even though bats rest while hanging from
the hindlimbs, they climb quadrupdeally. In fact, bats have
essentially arboreal limb proportions and structural strengths
(especially pteropodids): they are quantitatively like suspensory
primates in the forelimb structure from the shoulder down to the wrist.
It only diverges greatly from arboreal expectations in the hand
(Swartz and Middleton, 2008). The bat hindlimb is actually quite
unsuited for bipedal locomotion - the rotated femoral head makes for
good hanging but poor walking. They're really quite locked into quad
walking now. That doesn't mean that their ancestors were quad walkers,
but I do fail to see why we should assume a bipedal intermediate
(especially given that none of the potential outgroups to bats are
I also note that launch mechanics suggest birds as the only volant
group with bipedal ancestry: bats launch quadrupedally (if they can
launch from the ground at all), and pterosaurs very much seem to have
done the same. Birds are therefore the only one of the three that use
a hindlimb dominated launch initiation.
Peters 2000 showed, via Langobardisaurus/Cosesaurus/Rotodactylus and
Sharovipteryx that a bipedal phase was also a part of the pterosaur
story. There are no published alternate scenarios for the rotation of
the planted hand. And still no alternate genera proposed that test
closer to pterosaur origins.
The phylogenetic argument is stronger: if you're correct about the
placement of pterosaurs, and their immediate outgroups are bipedal,
then that would at least partially suggest bipedal ancestry. However,
I'm a bit confused on your last point: how is it that your favored
outgroups can be said to be objectively closer than those favored by
other phylogenetic hypotheses? Are you referring to branch support
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181