Re: New alvarezsaurid

["Matthew Troutman" <m_troutman@hotmail.com>]

>snip<

>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.

  The development of a carpometacarpus is for better control during 
flight. A better support for feathers and wing stability. The 
carpometacarpus in the Avimimus chimera is basically of a volant avain 
form. A true predatory carpometacarpus, as shown by phorusrhacids, has 
more phalangal mobility and the carpometacarpus is parallel to the 
radioulna, both of which were lacking in "Avimimus". 

 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.

    Actually, metacarpals II and III were closer together and metacarpal 
III was a thin, bowed split, a bad design for predation.

>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.

    This is not so. Though III did hold the primaries and secondaries, 
all of the "manipulation" of the flight feathers was done by the motions 
of the flight stroke.

MattTroutman

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