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Re: dino-lice



On 4/22/2011 5:20 PM, Jason Brougham wrote:

" ...the forelimbs of alvarezsaurids were greatly abbreviated and were certainly not 
used in locomotion..."

pg 115, Chiappe et al., 2002 L.M. Chiappe, M.A. Norell and J.M. Clark, The Cretaceous, 
short-armed Alvarezsauridae: Mononykus and its kin. In: L.M. Chiappe and L.M. Witmer, 
Editors, Mesozoic Birds: Above the Heads of Dinosaurs, University of California Press, 
Berkeley (2002), pp. 87–120.

If Chiappe did not specifically mention or consider the constrained conditions in which I posit locomotive uses for the forelimbs, then this citation is not relevant, is it?

On 4/23/2011 4:09 AM, Tim Williams wrote:

But the heavy-duty musculature indicates
the forelimbs were capable of applying a hefty force for some reason.

A locomotive use is logically attractive from the evolutionary perspective -- it explains both "excessive" musculature and progressive truncation of the forelimbs, as the generic haplocheirid morphology specializes to access constrained areas such as nests, burrows, hives, holes, hollow logs and carcass interiors with the head and neck.

Very short strong arms would be especially useful in extricating the front half of the body from cul-de-sacs and tight spaces.

Is there a specific mechanical reason this idea has been ignored? Were these animals completely incapable of moving their arms in such a way that the forces applied to the trunk were at some angle other than absolutely perpendicular to the spinal column?

I note that even in that case the arms would still be useful in the activities mentioned, although their utility would be reduced.

On 4/22/2011 12:52 PM, Jason Brougham wrote:

Now, it may appear that the processes for muscular attachment have enlarged 
from the ancestral state but they haven't. Not at all. They have only become 
RELATIVELY larger as the rest of the bone became smaller at a faster rate. I 
think that this has confused many workers, who may say that the limbs have 
become MORE robust when, in fact, they have only become wider relative to 
length  as, overall, they reduced to a tenth of their ancestral length.

Very interesting -- makes the whole question disappear. I like it, and thanks for the links. But haven't other theropods (and birds) reduced their forelimbs w/out creating a similar illusion? And don't such genetic events necessarily occur within species rather than among them?

I also read the Linhenykus paper this morning and checked the measurements on 
the forelimb. Linhenykus weighed the same as a large pigeon (C. livia), 450 
grams. It's hand was 17mm long, the same as your thumbnail, and the rest of the 
arm was about equal in length, so the whole pectoral limb was the same length 
as the last segment of your thumb. Wouldn't it take several kilograms of force 
to break the concrete - hard matrix of a termite mound? If so, if those tiny 
arms could somehow produce that much force, wouldn't the arm of Linhenykus push 
it strongly away from the termite mound before the mound cracked? The little 
fellow would be doing pushups!

Your implied point -- "The idea that these animals were using these limbs as tools to alter external objects is er, um, COUGH!, unconvincing..." seems unassailable to me...