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RE: comment-therizinosaurs

  My larger concern on this point is that the pedal unguals are also strongly 
compressed mediolaterally, enlarged, and recurved. The manual and pedal unguals 
are also, unlike those of fossorial or semi-fossorial animals such as aardvarks 
and tortoises, compressed; such "digging" unguals are broad transversely, 
especially on the palmar side, and generally flat, even in the unguals, or at 
least are broadly ovate rather than narrow and thin. This is true in mammals 
and reptiles, although I am unsure precisely in birds, though some studies 
exist examining the cross-section of the bony ungual or sheath relative to 
habitus. Such imply that the transversely narrow unguals are not diggers or 
likely usable for much substrate moving. 

  Cycad penetration? No clue.


  Jaime A. Headden
  The Bite Stuff (site v2)

"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 

> Date: Mon, 10 Oct 2011 18:23:03 +1100
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: comment-therizinosaurs
> Augusto Haro <augustoharo@gmail.com> wrote:
> > Interesting ideas...
> > Although I would hesitate in that relatively straight unguals are not
> > well suited for dealing with branches:
> Yes, and the manus of derived therizinosaurs was poorly adapted for
> any kind of grasping or hooking. The forelimbs were very different
> from those of ornithomimosaurs in particular.
> The basal therizinosaur _Falcarius_ still retains a raptorial manus.
> But in the later evolution of this group, the manus (at least, the
> non-ungual phalanges) became shorter and less adapted for grasping.
> The unguals lost the dorsal lip and collateral ligament pits (or
> nearly so) and became long and thin - especially in _Therizinosaurus_.
> Plus, the glenoid shifted more laterally, probably to increase dorsal
> reach. So whatever the forelimb was used for, it was deployed against
> something fairly large and high off the ground. The idea that these
> herbivores targeted the starchy pith of cycads is intuitively
> attractive, but the cycads (and similar gymnopserms) were in steep
> decline during the time when therizinosaurs were diversifying (later
> Cretaceous).
> The hypothesis that the hand claws were defensive weapons is in
> keeping with the slow, ponderous nature of therizinosaurs, and the
> lack of any other obvious defenses (although the beak could have
> delivered a nasty nip). Even titanosaurs had body armor or a whiplash
> tail - and/or they were really, really big.
> Cheers
> Tim