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Re: Theropod limbs - how mobile?



>And in the meantime he starves, doesn't he!?! -- As has been discussed very
>often onlist, that immobility is a great thing for such a predator, as this
>makes it much more difficult for prey to escape, relatively much easier --
>no muscular effort is required -- for the predator to hold it. And while
>it's holding its prey, it finishes it off by means of the sickle claw.
Looks
>like *Tyrannosaurus* likewise used its arms to hold prey in place -- not
up,
>not down, just in place -- and used its jaws to finish the job.
>
True, immobility could have served this purpose
>
>The paper in Mesozoic Vertebrate Life explains this. *T. rex* arms are
incredibly strong
>and not vestigial in any way. They are so short because this -- like in the
>mononykines -- brings maximal force at the expense of unnecessary velocity;
>dromaeosaur arms are built for maximal velocity instead, and human arms are
>a compromise for climbing. Take-home message -- unfortunately, one must
read
>the most expensive books available. :-)
>
But...there's always a "but", how incredibly strong were the arms of T.rex
and what was their limit of subduing or holding prey? Doubt they could have
held down a Anatotitan or Triceratops.
>
>The claw of *Velociraptor* isn't small at all.
>
Alright, maybe bad example, take the specialized Dromeosaurus than. It is
said at least to have a small pedal ungual II so I have to base the
following on that: like is said on HP Daniel Bensen' website, Dromeosaurus
had much more sturdies jaws than it's ancestors. A secondary specialisation,
which would have made up for the reduced pedal ungual. Different
specialisations might have occured which would have led to the reduction of
this killing tool, such as the here mentioned sturdier jaws and the
previously mentioned hands.
>
>> When something get's progressively shorter,
>
>Were they getting _progressively_ shorter? Aren't all known tyrannosaurid
>arms of pretty similar sizes?
>
Do I need to say more than: "Eotyrannus lengi"??? Second, the forelimbs of
several primitive Tyrannosaurids are not known from good material
(Alectrosaurus, Stokesaurus) or not known at all (Alioramus) to give precise
comparisons to Eotyrannus. At least, from the Early Cretaceous to the Late
Cretaceous the arms became progressively shorter within a span of about 50
milion years (maybe longer, maybe shorter) in the Tyrannosaur group.