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Re: Ceratonykus braincase described



 Augusto Haro <augustoharo@gmail.com> wrote:

> Nice... good eyesight seems not very suggestive of social insect
> hunting or excavation in general... Although it is not said how good
> sight it had relative to the non-alvarezsaur ancestral state.


Just when you thought it was safe to go back to the DML...    :-)


Good eyesight would be appropriate for scavengers that keep an eye out
for carcasses in the distance... either by sighting large carcasses
directly or the pterosaurs above heading in the direction of
carcasses.


On another alvarezsaur-related issue, Alifanov and Saveliev poo-poo
the proposed alvarezsaur affinities of _Haplocheirus_.  I initially
didn't understand their reasoning: "because the manus of this species
displays typical theropod features."  But it's apparent later on in
the paper that the authors have some pretty heterodox views on the
evolutionary history of alvarezsaurs.  Front-and-center is their idea
that the ancestors of alvarezsaurs were arboreal.  Thus, the authors
also the tip the bucket on the hypothesis that the forelimbs of Late
Cretaceous alvarezsaurids were specialized for digging, instead
proposing that the forelimbs were truncated as part of the adoption of
cursorial behavior, as in ostriches.  The monodactyl forelimbs,
according to Alifanov and Saveliev, are a relict of that arboreal
lifestyle: alvarezsaur ancestors were tree-climbers, and so had long
immobile forelimbs tipped with a large claw for hooking branches.
(They must be thinking of sloths; most arboreal mammals have highly
mobile forelimbs that are quite often prehensile as well.)
Alvarezsaur forelimbs shrunk when the creatures shifted to a
cursorial/terrestrial ecology, but they retained the immobile,
monodactyl morphology.


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.


Instead, _Haplocheirus_ is "tentatively" regarded by Alifanov and
Saveliev as a relative of the Coeluridae or Compsognathidae.
Personally, I would love to see compsognathids on the line leading to
late Cretaceous alvarezsaurs: it would fill in the Late Jurassic -
Early Cretaceous ghost lineage, and show key steps in the
transformation of the forelimb.  But, alas, a
compsognathid-alvarezsaur clade is not what current phylogenetic
analyses are showing (although certain phylogenies show
Compsognathidae and Alvarezsauria as successive outgroups, which is
interesting IMHO).  In any case, a compsognathid-alvarezsaur link is
not what Alifanov and Saveliev are arguing, because they remove
Alvarezsauria from Theropoda altogether!  Outside of the work on the
_Ceratonykus_ brain cast, the ecomorphological component of the
Alifanov and Saveliev paper is bad science.  Linking alvarezsaurs to a
hypothetical, arboreal, non-theropod ancestor reminds me of the
efforts by Feduccia &c to link birds to a hypothetical, arboreal,
non-theropod ancestor (presumably not the same imaginary ancestor).



Cheers

Tim