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Subject: pectoral muscles
I just read Carl Zimmer's cover story about the armed Titanis in the June 1997
of Discover. He mentioned that, due to the large pectoral muscles Titanis
inherited from its forebears, its arms must have prodigious strength that would
have been handy in grasping prey.
At first glance, it is a logical conclusion. But then I thought about chickens.
Galliform birds like chickens have large pectoral muscles like most other birds
but are generally weak flyers (except for migratory quail) as they spend much
of their time on the ground and fly in short, quick bursts. Anyone who savors
chicken breasts can appreciate the white meat of the pectorals, which is the
result of a lower hemoglobin content than, say the legs.
So now the question is raised. Are large muscle attachments on bones sufficient
evidence to say that the associated muscles could be used strenously over a
long period of time? Or is this the wrong way to approach it? Titanis may have
had large pectoral muscles, but perhaps they weren't high in hemoglobin. Would
such muscles be sufficient to allow Titanis to swipe at its prey and pin it
down? If we envision a scenario between Titanis and a pronghorn antelope (the
scene depicted in the article), Titanis would be swiping at the antelope,
taking stabs with its large dagger-like main claws and trying to grasp unto
its victim by pinning it between the large and small claw. Such a death
struggle would hardly have been a long, protracted event, so perhaps Titanis
didn't need "hemoglobin rich" breast muscles. Maybe "white meat" muscles were
sufficient for the job.
What is the relative size of a chicken's pectorals compared to a flying bird of
similar size? If they are close, then perhaps it is suspect to assume that
large muscle attachments support "hemoglobin rich" muscles that can function
continously over a long period of time. I remember a debate some time ago (not
necessarily on this list) about just how strong tyrannosaur arms really were.
I'm just speculating here so I don't know how much of my arguments really will
Mines and Geosciences Bureau
PS. Where can I get a detailed article about Robert Chandler's work on Titanis?
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