Re: New alvarezsaurid

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

Dinogeorge writes:

<In a message dated 98-03-23 16:49:22 EST, m_troutman@hotmail.com 
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. 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 BCF, the manus becomes 
elongate and stiff because this is a clear aerodynamic advantage...>

Is this in any way similar to the carpometacarpoid form of *Avimimus'* 
manus? In Kurzanov 1981 (or 1983) the metacarpals are shown partially 
fused to one another. This would definately have stabilized the manus, 
for the metacarpals would not have slid against each other as they do in 
our hands, a proven grasping method. All grasping mammals (raccoons and 
kin, primates and kin, etc., many marsupials) all have freely set 
metacarpals, that allow movement of each bone independant of one 
another, while Archie and dromies all had the first and second 
metacarpals rigidly set to each other, strengthening the resistence of 
countering force applied the manus at large (I'm not a physicist, but I 
think I've got the concept put through right :-) ) and only mc III was 
free of the manus's restrictions.

And even though ornithomimids had the mc I-II phalanx turned slightly 
inward and could thus perform a marginal grasping effort, the 
metacarpals are locked against each other, making the mc's immobile of 
each other, but still offered a fair usage on the wrist and digits.

Anyway, this form in Archie allowed digit III to flex the skin that 
wrapped the "palm" of the hand and manipulate the feathers (flight 
feathers), or to pull that digit partially inward towards the others in 
a sort of reversed thumb. How far it could do this, I don't know, but 
the proximal end of mc III is loosely set to mc II.

Try this: take the first knuckle of each finger and wobble it around 
(its easier on digit V and gets harder towards II, and is most flexible 
at I {i.e, the thumb}). MC's II and III are set against each other in a 
more or less broad articulation, while IV and V are much less broad and 
looser by consequence. Now, take a small rubber ball (or any object that 
can fit in you hand) and wrap your fingers around it; notice that the 
knuckles follow the fingers to a degree, actually wrapping around the 
object themselves. Archie's hand could do this, but the palm was so long 
and narrow that it would have served no other purpose than to give the 
finger a better position when grasping something, such as a branch, 
lizard, bug, or whathaveyou. Even to modulate the flight feathers, such 
as shaking them, fanning them, or whatever.

Jaime A. Headden

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