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RE: Haplocheirus does not confirm alvarezsaurs are maniraptoran

The trick with fossorial animals is to expel earth _posterior_ or_lateral_ to 
the animal, so that the refuse of the effort does not fill the hole to be 
produced.  The classic theropod manus position has the palm face medial and 
towards its opposite, while the arm's action is arguably stronger 
mediolaterally than cranioposteriorly.  Typical mononykids manus orientation 
seems to be medial-facing, with the action of the arm folding being 
cranioposteriorly, so that the manus orientation was perpendicular to the arm's 
action.  In a recent SVP (2007?) there was a result that rotated the arm and 
scapulocoracoid of at least onem alvarezsaurid could be oriented so that the 
manus faced caudally, but at this point the arm action/manus action are still 
not aligned which begs comparison to other diggers.


Jaime A. Headden

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> Date: Fri, 29 Jan 2010 11:51:45 +0100
> From: david.marjanovic@gmx.at
> To: dinosaur@usc.edu
> Subject: Re: Haplocheirus does not confirm alvarezsaurs are maniraptoran
>> Enough grousing... _Haplocheirus_ is a really, really interesting
>> critter. It would seem that the peculiar functionally monodactyl
>> manus of derived alvarezsaurs evolved *after* the forelimb had
>> reduced in size. This is strange, because if the forelimbs were used
>> to rip open insect nests (either mounds or soft wood), why was the
>> reach of the manus *decreased*? This goes against the playbook of
>> extant ant-eaters.
> Ant-eaters don't need reach. (They can just walk closer.) They only need
> power.
> The trick is that all extant ones are (to varying degrees, but still)
> quadrupedal. To be useful in locomotion, forelimbs need a minimum
> length. Compromises result that the bipedal alvarezsaurids simply didn't
> need.
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