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

[Jaime Headden <qi_leong@hotmail.com>]

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?