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All these look to me as logical possibilities. I was also thinking on
the similarity between not very curved, laterally compressed unguals
and the condition in bears, which have similar claws in all limbs.
Bears, being relatively smart mammals, appear to use them in a variety
of ways, for example defense, offense, turning rocks, unearthing food
(would not this mean that these blade-like unguals can be used when
digging for food, instead of cave-making?), etc.. Less smart dinosaurs
may have used them in less varied ways, agreeing also with their less
flexible articulations. What if their blade-like shape has more to do
with resistance on a dorso-ventral sense than acting like blades?
Besides, most sloths (living and fossil) I can remember do not have
strongly curved claws, so perhaps slightly curved claws are not so bad
when dealing with branches.
2011/10/11 Tim Williams <email@example.com>:
> Augusto Haro <firstname.lastname@example.org> wrote:
>> Instructive point (congratulations dude, it's incredible how much you know!).
>> But, were there enough cycads, or similarly though plants, to allow
>> therizinosaurs prospering by eating them? Because a group which
>> declines in taxonomic diversity may still be a conspicuous element of
>> the biota.
>> If not, it has been hypothesized that ceratopsians, which also
>> diversified close in time, also dealt with though plants. Ostrom
>> considered Triceratops was feeding upon palms and cycads, later others
>> stated that they may be feeding on though ferns, which were more
>> abundant. May something like that also apply to therizinosaurs? Long
>> and blade-like claws may be useful for some plant with a robust main
>> body protected by hard (preferably flexible) walls but with some
>> softer inside.
> Even among the derived/post-_Falcarius_ therizinosaurs the function of
> the forelimbs probably varied between individual taxa. Although the
> claws of _Therizinosaurus_ were very long and blade-like, those of
> taxa like _Nothronychus_ and _Erliansaurus_ were shorter and strongly
> recurved. So it is possible that the latter used their manus to help
> procure food, whereas the extreme condition in _Therizinosaurus_ was
> tied solely to the use of the forelimb as a weapon.
> That doesn't rule out less derived therizinosaurs also using their
> hand-claws for defense - these pot-bellied herbivores certainly
> couldn't run from danger. But it may be that the trophic role of the
> forelimbs became progressively less important, and the long claws of
> _Therizinosaurus_ took on a role in defense against potential
> predators, or in sexual display (as suggested by Zanno, 2006). The
> giant claws could have been like the antlers of the "Irish elk", and
> not even used for intraspecific combat.