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Re: Ceratonykus braincase described

Brad McFeeters <archosauromorph2@hotmail.com> wrote:

>> So I can see why Alifanov and Saveliev would not want a "typical
>> theropod" like _Haplocheirus_ to be ancestral to Late Cretaceous
>> alvarezsaurs like _Ceratonykus_ and _Shuvuuia_: it destroys their
>> arboreal hypothesis.
> No, it is just as easy to imagine that alvarezsaurs passed through their 
> hypothetical sloth-like arboreal phase in the Early Cretaceous, in forms more 
> derived than *Haplocheirus*.

Alifanov and Saveliev (2011) regard _Haplocheirus_ as a theropod, but
regard alvarezsaurs as non-theropodan dinosaurs.  So for what it's
worth, they would disagree with you.  Frankly, I find any arboreal
phase in the evolution of alvarezsaurs difficult to imagine -
especially anything resembling a modern tree sloth.  Derived
therizinosaurs have been regarded as ground sloth analogs - but that's
a whole different matter.

It's also worth mentioning that although there is no doubt that
alvarezsaurs were theropods, their placement inside Maniraptora is a
little precarious.  Choiniere et al. (2010) noted that an
Alvarezsauria-Ornithomimosauria clade required only one additional
step compared to having Alvarezsauria nested inside Maniraptora (the
most parsimonious topology).