[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

RE: pterosaur femora sprawl




I don't have too much to add to Mike's post.  (It's one of those posts that 
says everything I would have wanted to say, only more articulately).   As a 
postscript, I'll only mention that if the origin of avian flight had an 
arboreal component, then such pre-avian maniraptorans would probably have 
climbed trees in a quadrupedal fashion, and may have employed all four limbs in 
gliding (microraptor-style).  Either or both may have influenced the evolution 
of the flight apparatus of early birds.


Cheers

Tim



>> 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
> bipedal).
>
> 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
> methodologies?
>
> Cheers,
>
> --Mike
>
>
> Michael Habib, M.S.
> PhD. Candidate
> Center for Functional Anatomy and Evolution
> Johns Hopkins School of Medicine
> 1830 E. Monument Street
> Baltimore, MD 21205
> (443) 280 0181
> habib@jhmi.edu

_________________________________________________________________
Change the world with e-mail. Join the i’m Initiative from Microsoft.
http://im.live.com/Messenger/IM/Join/Default.aspx?source=EML_WL_ChangeWorld