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Re: dino-lice



I think the straight face test me need to be invoked here.

On 23 Apr 2011, at 15:06, Don Ohmes <d_ohmes@yahoo.com> wrote:

> 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...