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As Senter pointed out, the olecranon increased moment of the forearm extensor
lever, advancing with the claw morphology a "hook-and-pull" mechanism. This
does not necessarily translate to a "tear things apart" mechanism. While Senter
disavowed "hugging" as the limbs could not actually close on one another, the
large sternum seems to brace muscles (M. pectoralis) that have little to do
with the "hook-and-pull," as this is further advanced by muscles of the
posterior humerus and scapula, not medial brachial muscles. It should be noted
that other predominant diggers lack such a keeled sternum, including anteaters
or aardvarks or moles, while possessing the remaining limb-based adaptations.
This implies the sternum has little to do with the arm-based behavior being
M. pecotralis expanded onto a sternal ridge might actually increase the
strength of the muscle when the limb is retracted if the arm were also slightly
rotated, forcing the angle to pull the humerus forward as well as medially. How
this works in a clutching or "hook-and-pull" mechanism, I have no idea.
Jaime A. Headden
The Bite Stuff (site v2)
"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
> Date: Wed, 20 Apr 2011 21:11:06 -0400
> From: GSP1954@aol.com
> To: firstname.lastname@example.org
> Subject: Re: dino-lice
> 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
> does not explain any of the features.
> In a message dated 4/20/11 2:46:08 PM, email@example.com 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.