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RE: Alvarezsaur spurs (was Re: dino-lice)



While there are some similarities, including the development of a single 
digital claw, the distinctions are also marked:

  Alvarezsaurids have a humerus, ulna, and radius was extremely developed 
attachments for associated muscles, and are also developed in such a way that, 
aside from the ulnoradial-humeral joint, there was absolutely no movement 
possible in the major arm joints. At the manus, a short, highly reduced 
carpomet block is joined with [rather than a reduced] an extremely enlarged 
first digit and ungual with developed proximal (read: metacarpo-phalangeal) 
flexor processes, while the unguo-pahalngeal joint shows indication of high 
mobility, but limited or absent flexor processes. The ulna possesses a highly 
derived olecranon process, almost 1/3 the bone's length, and instead of being 
slender, the humerus is short and nearly as broad across the epicondylar crests 
as it is long. It is also unlikely the limb could extend or fold in an avian 
manner: virtually all mobility, despite an unrestricted ulnoradial-humeral 
joint, occurs between two areas: the humerus and the scapula, and MDI-1 and 
MDI-2. alvarezsaurids have a fixed coracoid, and a keeled sternum, and the 
coracoids according to sternal morphology approach one another closely, fairly 
distinct from the brachial arrangement in kiwis.

  It should be noted that the angle of action by which motion between the above 
two joints occurs almost 90 degrees from one another, such that they could not 
act in the same plane of motion. Forelimb retraction, through the 
scapulo-humeral joint, pulls the manus into a nearly vertical position, while 
phalangeal flexion folds the digit in on itself. As Senter noted, the limbs 
could not touch one another (I know, neither can kiwis). The primary issue here 
is that the forelimb in alvarezsaurids is developed in such a way that large 
degrees of motion are inhibited, the limb is just as tiny as in kiwis, but the 
bones are excessively developed.  

Cheers,

Jaime A. Headden
The Bite Stuff (site v2)
http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)





________________________________
> Date: Thu, 21 Apr 2011 02:51:02 -0600
> Subject: Re: Alvarezsaur spurs (was Re: dino-lice)
> From: paleeoguy@gmail.com
> To: qi_leong@hotmail.com
> CC: d_ohmes@yahoo.com; dinosaur@usc.edu
>
> Not to be blunt, but has no-one here ever seen a Kiwi skeleton?
>
>
> Lee Hall
> Paleontology Undergraduate
> Museum of the Rockies
> Montana State University
> Bozeman, MT
> lhall@montana.edu
> http://sites.google.com/site/leehallpaleo/Home
>
>
>
> On Thu, Apr 21, 2011 at 2:07 AM, Jaime Headden
> > wrote:
>
> Here's an idea (probably not an original one, but it comes to me when I
> read this):
>
> Alvarezsaurs are almost certainly hyper-precocial, meaning they are
> independent and highly active from hatching, including hunting and
> avoiding predators, without parental care. This would result in
> advanced fusion of vertebral and limb elements, but not necessarily in
> cranial and accessory elements (sternum, advanced development of the
> forelimbs, development of the cnemial crest, etc.). We should be able
> to test this by analyzing size-independent development criteria, which
> can discern precocial from altricial young, and extrapolate these
> criteria onto alvarezsaurids. I suspect, although am not certain, that
> some taxa named from Mongolia and northern China may be precocial
> young, and the seeming odd trend of decreasing size during evolution of
> the _Alvarezsauridae_ is an artefact of recovering young.
>
> An additional effect would be partitioning of food choices by age and
> forced development of cursorial features that would be retained in
> as-yet-undiscovered adults, while earlier morphologies that were not
> required in adulthood would become more vestigial. This occurs with
> tooth morphologies, jaw mechanics, etc., associated with varying
> feeding changes through ontogeny, and occurs in limb design, but
> assigning this concept to the anterior limbs requires finding
> differential morphology in them among ages which differ from those of
> the hindlimbs, and so far all alvarezsaurids -- or rather, for some,
> "parvicursorines" -- have the same form of the forelimbs across
> specimens.
>
> Food for thought, perhaps.
>
> Cheers,
>
> Jaime A. Headden
> The Bite Stuff (site v2)
> http://qilong.wordpress.com/
>
> "Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
>
>
> "Ever since man first left his cave and met a stranger with a
> different language and a new way of looking at things, the human race
> has had a dream: to kill him, so we don't have to learn his language or
> his new way of looking at things." --- Zapp Brannigan (Beast With a
> Billion Backs)
>
>
>
>
>
> ----------------------------------------
> > Date: Wed, 20 Apr 2011 10:09:50 -0400
> > From: d_ohmes@yahoo.com
> > To: dinosaur@usc.edu
> > Subject: Re: Alvarezsaur spurs (was Re: dino-lice)
> >
> > On 4/20/2011 3:46 AM, Tim Williams wrote:
> >
> > > I don't want to extrapolate too much from this,
> > > because alvarezsaurs are not mammals; but an exclusively
> > > myrmecophagous diet is hard to accord with the high BMRs indicated by
> > > the highly cursorial proportions of alvarezsaurs.
> >
> > Ah yes, the tall, bipedal, highly cursorial, long-necked, long tailed
> > anteater with nest-destroying arms just slightly longer than it's head
> > and considerably shorter than it's neck -- who could not be convinced by
> > such a picture? :)
> >
> > To take a slightly different tack -- is there support in the extant
> > biosphere for a scenario in which the arms were relatively longer and
> > hence more useful in this creature's early lifestages? In other words,
> > do we know of animals (preferably avian) wherein one part of the body is
> > necessary when juvenile but is outgrown by the rest of the body and
> > becomes "vestigial" as they become adults?
>
>