Re: New alvarezsaurid

["Jaime Headden" <jaemei@hotmail.com>]

Matthew Troutman writes:

< <<Regardless, a mobile manus is not a predatory design. A manus where 
the phalanges are parallel to the radioulna is better for "prey 
handling" because it resists strain and is inheritantly more stable.>>

<I don't think that this has ever been demonstrated or even can be
demonstrated; I don't even know what "better" means in this context.>

I mean mobile in the way the semilunate makes it mobile. "Better" 
in this context means 'more suitable'. 

<If all you have is a mobile manus as a predator--inherited from 
ancestral forms that had a mobile manus for grasping and climbing in 
trees, for example--then that is what you have, and you make the best of 
it. If you believe that a manus such as you describe is "better" than a 
mobile manus, you should show why you believe this.>

In phorusrhacids, the ancestral manus was of a flying form, and it 
did not stay that way. I ask _why_ did phorusrhacids lose the ability 
for the manus to "swivel"?>

No need to "snap" the manus out from the folded position. In fact, not 
being able to perform the folded position. The block would have served 
in the form it did in primitive theropods like coelophysoids, just 
curling the manus in, palm oriented caudorostrally. _Why_ is beyond be, 
but atavism from such a form as flying is a specialization that also led 
to redevelopment of separate phalanges and claws, the paedomorphic 
characters that *Phorusrhacos* and *Titanis* enjoyed (or was it just the 
latter?) and the only obvious reason would be predation that did not 
neccesarily need to use the massive beak to totalized. Did this mean the 
prey it sought was large, aggressive, or powerful enough to require 
_arms_ to subdue? or did he just use them as tools that had nothing to 
do with meal-catching? Rending flesh (post mortem), courtship (I have no 
idea!), rivallry, etc..

To continue:

<Attention must be put on the function of the forelimb and manus of 
phorusrhacids. They both were used for subduing prey; using this exapmle 
you can see that a manus with limited rotation can be used for prey 
seizing. Most birds have a rounded carpal block, which allows them to 
tuck their wing. Phorusrhacids have a squared carpal block, which means 
that the manus lies parallel to the radioulna. Using the phorusrhacids 
as an example, it can be shown that a stiffened manus in the sense of 
rotation, is very advantageous for bipedal predators that are similiar 
to theropods. 

I am not saying that maniraptorans were not predators, just that the 
manus is incongruent with the notion that it can be used for grasping 
and prey handling.>

Such a manus would have reduced the shock of prey trying to escape, 
where the reflex to being hit would be to back away or "fold", the bird 
would keep its grip (a fisher, perhaps?) by resisting that reflex, and 
that would help subdue the struggling prey as the enormous beak snapped 
down on the neck, or brained the creature.

Jaime A. Headden

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