Re: Gigantoraptor stuff

[Tim Williams <twilliams_alpha@hotmail.com>]

Pedro Andrade wrote:

> Even if Gigantoraptor is not Deinocheirus,

In the most recent analysis, _Deinocheirus_ came out as a gigantic 
ornithomimosaur, close to _Harpymimus_.

> this thing
> bugs me: is there any special reason why Late
> Cretaceous maniraptoriforms in Mongolia grew so large?
> Apart from Gigantoraptor and Deinocheirus there's also
> giant therizinosaurids and Achillobator.

Yeah, it bugs me too.  Maniraptoriforms appear to have radiated into the 
"large herbivore" role dominated by sauropodomorphs and ornithischians.  In 
Iren Dabasu, for example, there are plenty of theropods, a few runty 
hadrosaurs, but no sauropods (AFAIK - if I'm wrong on this, please let me 
know).  Derived therizinosauroids appear to have been herbivores, and the 
same might be true of at least some oviraptorosaurs (hence my previous 
comparison of _Gigantoraptor_ to _Dinornis_).  I don't know about 
_Deinocheirus_ - although its placement among basal ornithomimosaurs 
suggests that it was perhaps not a ferocious predator... but I wouldn't want 
to go too far with that.  Somebody had the intriguing suggestion that 
_Deinocheirus_ was specialized for digging up small ornithopods from their 
burrows (which, if nothing else, would make for a great illustration).

But _Achillobator_ was certainly a predator.  It had plenty of big 
herbivores to go after.

> Why did this happen in Mongolia and not say, North America?

It might have - especially if tyrannosauroids are maniraptoriforms.  North 
America also had large dromaeosaurs (e.g., _Utahraptor_), some 
therizinosauroids, and at least one large oviraptorosaur (undescribed; and 
not as humongous as _Gigantoraptor_).

Hope that helped.

Cheers

Tim

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