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Re: dino-lice



On 21 April 2011 02:11,  <GSP1954@aol.com> wrote:
> The extreme musculature indicated by the ossified keeled sternum and big
> olecranon process combined with an enormous claw leave little doubt that
> alvarezsaur arms where for tearing something apart. The shortness of the arms
> increased their power via leverage. I like to think it was termite mounds,
> which I believe have been discovered from that time. Display feather 
> fluttering
> does not explain any of the features.
>

The big olecranon is interesting (anyone done any mechanics on it?
compared it quantifiably to fossorial mammals?), especially with, as
GSP says, the short outlevers.   But the very large disparity between
the limb lengths does mean it would have to be squatting on whatever
it was digging, or pressed right against it. And it undeniably already
has two large, powerful pelvic limbs to dig with.

Hmm. Problem with the feather fluttering (which does go some way to
explaining large pectorals) is that the lever ratio should be the
other way around at the elbow. Although a short humerus decreases the
moment arm at the shoulder, which equals more rapid movement (although
you'd need to actually measure the distance from the glenoid to the
deltapectoral crest, could be relatively lengthened). Problem with
digging is that the rest of the body doesn't really fit, and things
with relatively enlarged, muscular hindlimbs that need to be do a lot
of heavy work would probably use their hindlimbs.

> In a message dated 4/20/11 2:46:08 PM, jaseb@amnh.org writes:
>
> << The problem with imagining Mononykus tearing open conifer cones with its
> arms is the same as picturing it digging into insect mounds. It couldn't
> reach the ground from a  standing position. Its arms, fully extended,
> could not even reach the knee.
>
> Present company considered I'll engage in a little a priori speculation
> and say that it seems unlikely that there would have been selection
> pressure toward shorter, reduced, arms in your scenarios. If shorter arms
> went along with clawing behaviors then we are imagining an animal that
> would have to squat down on top of an anthill and then dig under its
> belly, as a storm of angry hands poured out over its body. The arms could
> have maintained their ancestral, long, state and functioned just fine in
> opening insect colonies, bark, or pinecones.
>
> According to Senter(2005) Mononykus also could not hold anything between
> its hands.
>
> Selection pressure could have driven shorter arms with larger muscular
> processes if there was selection for high frequency fluttering of a fan of
> feathers or ribbons.
>
>  >>
>
> </HTML>
>