RE: New Deinocheirus specimens found, indicating basal ornithomimosaur

["Thomas R. Holtz, Jr." <tholtz@umd.edu>]

The manual claws of Deinocherius are most definitely NOT raptorial! However, I 
understand when just viewing them from a distance
they might appear so. Handling the actual specimens (or casts), you find they 
are much thicker, much less pointed, and so forth than
people commonly think: more like the claws of basal therizinosauroids.

Torvosaurus, Suchomimus, megaraptorans, etc., are much better models for what a 
giant raptorial claw actually looks like: far more
tapered, far more pointed, more elongate compared to the articular facet, etc.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA
> -----Original Message-----
> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of 
> Jaime Headden
> Sent: Tuesday, November 05, 2013 9:32 PM
> To: Tim Williams; Dinosaur Mailing List
> Subject: 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