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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