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RE: New Deinocheirus specimens found, indicating basal ornithomimosaur



Based on the shoulder morphology, I'd have to agree with the absence of a 
raptorial prey-holding function, but then that's too easy a statement to come 
by. To hold prey to you using arms effectively, you'd have to use pretty robust 
limbs and unfortunately the muscle sites for shoulder muscles do not lend 
themselves for resisting the forces that would be brought to bear. I can make 
an offhand comment that I doubt *Deinocheirus* could resist the struggles of an 
animal half its mass, but that's an offhand comment and I can't back it up.

As others have pointed out, however, prey-restraint is predominantly foot or 
jaw based, not forelimb-based. If you can stand on your prey, you are using 
your entire body's weight against the prey animal, and as such the arms are 
even less important.

That all said, the shoulder indicates low mobility, and the wrist low 
flexibility, which would make better single-direction force resistance better, 
and in a plane parallel to the long axis of the body. As such, it looks to have 
good gripping, but not for objects of very large size. And again that comment 
above about offhand remarks, I don't think it could even pick up something a 
quarter its weight.

But for an animal with "raptorial" claws, there are many possible functions. 
Being trenchant and broad, the claws resist vertical compression at the tip and 
to some degree sheer forces and oblique sheer as the claws are roughly oval and 
not flattened towards the venter. Thus, they'd be fairly good for tearing and 
piercing. And that's about it.

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: Wed, 6 No
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: New Deinocheirus specimens found, indicating basal 
> ornithomimosaur
>
> Luis Rey <luisrey@ndirect.co.uk> wrote:
>
>
>> On top of that, it has a link to my very old Deinocheirus
>> reconstruction. I have to say: I think my head was not too far off
>> the "missing" material I might have heard the rumours of ..,
>> somewhere...
>>
>> I simply CAN't wait to have everything in my hands to do my own
>> proper reconstruction.
>
>
> Nor can I. (By which I mean I can't wait for YOU do a proper reconstruction.)
>
>
> As a large and rather bulky herbivore, the "terrible" forelimbs that
> give _Deinocheirus_ its name are incongruous. The manus is certainly
> raptorial, and the forearm was capable of much more rotation than was
> typical for ornithomimosaurs. Overall, the _Deinocheirus_ forelimb is
> fairly slender - so it was unlikely to have been used to grasp or hold
> prey (which would be odd for a herbivore in any case).
>
>
> My guess is that _Deinocheirus_ used its long "raptorial" forelimbs as
> a defensive weapon against approaching predators. Unlike the smaller
> and more cursorial ornithomimosaurs, big _Deinocheirus_ wasn't blessed
> with speed. So, like the comparably sized _Therizinosaurus_ (which
> was probably even bulkier), _Deinocheirus_ might have used its long
> forelimbs to help keep potential attackers at a safe distance.
>
>
>
>
>
>
> Cheers
>
> Tim