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RE: New paper on pre-Archaeopteryx coelurosaurian dinosaurs



  At least *Therizinosaurus cheloniformis* is known from multiple claw and one 
forelimb/shoulder specimens, and one referred hindlimb of a segnosaur of such 
size to match the forelimbs relative to what is known in smaller segnosaurs; 
*Deinocheirus mirificus* is supposedly supported by additional undescribed 
material.

  A reduction or low variety in known sauropods from the Mongolian sequence 
implies a lack of support for the ecological niche or that other taxa were 
filling it, and competing with said sauropods (which, despite Mike's 
favoritism, are not the all-time hottest dinosaurs around ;)); this latter fits 
in with what Tim suggests to a degree, but it requires some better 
understanding of the potential feeding habits of said dinosaurs.

  *Deinocheirus mirificus* -- if correctly identified as a large 
ornithomimosaur -- would likely have had a small, narrow, and shallow skull, 
and this would agree with *Therizinosaurus cheloniformis* (again, assuming 
correct identification and correlation despite size). But in *Gigantoraptor 
erlianensis*, the skull (as implied by the jaw) is short, and very broad, and 
also very deep. This is similar to some sauropod jaws (as in *Brachiosaurus 
brancai*) but not others (as in *Nemegtosaurus mongoliensis*) in which the jaw 
is relatively shallow, narrow, and the dental arrangement further restricted. 
If the toothless theropods supposedly occupying the "sauropod niches" were 
doing so on a consistent basis, they should match said sauropod's jaw forms, or 
compensate adequately, but I do not recall any sauropod matching a narrow, 
shallow, and small skull design on the order or therizinosaurs or 
ornithomimosaurs. Aside from the degree of rostral edentulousness in the 
theropods, skull shape implies that some of these theropods were feeding in a 
manner unlike sauropods, and this implies some degree of variation from the 
"sauropod niche" that is mid- to high-browsing. If what I argue is true, then 
only one theropod (*Gigantoraptor erlianensis*) closely conforms to a jaw 
design that would compete with sauropod jaw design, while those of other 
theropods indicate a different ecology.

  As such, I would then state that the brevity of sauropods probably has 
nothing to do with the appearance of mid- to high-browsing herbivorous 
theropods being more plentiful in the later Mongolian Mesozoic sequence.

  Of course, this means nothing unless we can even closely approximate dietary 
ecology in these particulars: a lot of this makes the broad (and I think 
intrinsically problematic) claim that sauropods were selective high-browsers, 
or that even their dentition was suited to this, or that they were so 
high-browsing as to be vertical necked, and approximating this with some 
reconstructions of ornithomimosaurian, therizinosauroid, or oviraptorosaurian 
theropods. Getting the physical biology and the general ecology straight would 
go a long way to helping compare the two groups of animals before we make more 
claims to speculating on their out-competing one another.

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





----------------------------------------
> Date: Fri, 29 Oct 2010 10:00:18 +0100
> From: mike@indexdata.com
> To: tijawi@gmail.com
> CC: dinosaur@usc.edu
> Subject: Re: New paper on pre-Archaeopteryx coelurosaurian dinosaurs
>
> On 29 October 2010 07:21, Tim Williams  wrote:
> >> Nevertheless, _Gigantoraptor_ is a BIG theropod.  You have to wonder
> >> what it was with Late Cretaceous Mongolia that prompted the emergence
> >> of such massive theropods.  More importantly, forms like
> >> _Therizinosaurus_, _Deinocheirus_, _Gigantoraptor_ were probably
> >> non-carnivorous.
> >
> > If these big-ass coelurosaurs were browsing herbivores, what factors
> > allowed them to occupy these large-bodied-herbivore niches in the
> > first place?  Why weren't the sauropods doing it instead?  After all,
> > the sauropods had been feeding this way since the Late Triassic, and
> > they let themselves get shoved aside by some opportunistic
> > johnnies-come-lately.  Sauropods are slackers, that's what I think!
>
> Oi! Let's not forget our buddies Nemegtosaurus, Quaesitosaurus (if
> distinct) and Opisthocoelicaudia. I'm prepared to admit that, known
> as they are from one specimen each, they were not exactly dominating
> the landscape like they did in the Morrison, but then Therizinosaurus,
> Deinocheirus and Gigantoraptor are also known from one specimen each.