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Re: Haplocheirus does not confirm alvarezsaurs are maniraptoran




Michael Mortimer <mickey_mortimer111@msn.com> wrote:

 
> See my preliminary blog post at 
> http://theropoddatabase.blogspot.com/2010/01/haplocheirus-jurassic-alvarezsaur-is.html
> for some early thoughts.  More detailed analysis to
> follow.


Yes, the rationale behind this latest definition of Maniraptora is not 
immediately clear ("_Ornitholestes_, _Archaeopteryx_, their most common recent 
ancestor and all of its descendants.")  The thing is, using the topology in 
Choiniere et al. (2010), the content of Maniraptora is the same as it would've 
been under Sereno's (2005) node-based definition ("Most inclusive clade 
containing _Passer_ but not _Ornithomimus_).  This is because Choiniere et al. 
(2010) recovered Ornithomimosauria as sister taxon to their Maniraptora (the 
clade bracketed by _Ornitholestes_ and birds).  I'm left scratching my head at 
this one.


The trouble is, without defining Maniraptora such that it explicitly *excludes* 
Ornithomosauria, we could arrive at a topology in which Maniraptoriformes is a 
subset of Maniraptora, depending on whether Ornithomimosauria or _Ornitholestes 
ends up as closer to birds.  Not good.


To quote the great philosopher Milhouse Van Houten: "I've said 'Jiminy 
jillikers' so many times the words have lost all meaning!"  Well, I've seen so 
many definitions of Maniraptora that the name has lost all meaning!  ;-)


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.


Cheers

Tim