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Re: Theropod limbs - how mobile?

David Marjanovic wrote:
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.
Can somebody please tell me why they think this is so? But first, try these simple experiments. You'll need a pair of hands and an angry cat. Holding your fingers rigid, and your hands facing inward, try to grip the struggling cat.  After applying ointment and plasters, try again, this time with your full range of mobility. Which works better?
Secondly,  partially bend your right index finger. Now press it against your  left hand. Move your left hand about a bit. You'll notice that the flexibility of your digit improves both contact and safety. If you try it again, this time with your finger straightened and bent back till it is immobile, not only is it less use, it is also in serious danger of getting broken!
David Marjanovic also said:
*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.
Tom Holtz has shown that Tyrannosaurs had skulls, teeth and necks designed to take serious torsional loadings - they didn't need to hold prey with their arms. Big theropods in general are not built to grapple with prey, they don't have the flexibility of mammalian carnivores.
David Marjanovic also said:
Were they getting _progressively_ shorter? Aren't all known tyrannosaurid
arms of pretty similar sizes?

A quote from PDW "in Tyrannosaurus and even more so in Albertosaurus the forelimbs became ever smaller with time and were on their way to complete loss"

Just to start even more debate, if we follow Greg Paul and view Archaeopteryx as a basal dromie, then with things like the new feathered dromie, Bambiraptor, Sinornithosaurus and on through Dienonychus and Velociraptor, then dromie forelimbs seem to be reducing with time (and also size?)

Any thoughts?