Re: pectoral muscles

["Matthew Troutman" <m_troutman@hotmail.com>]

<<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.>>

According to Terry Jones, it is possible that the galliform resting 
metabolism is lower than most other birds, presumeably because of the 
incised sternum which would mean that the airsacs are not being 
ventilated to the same as other birds.  The same is maintained for 
tinamous.  The deeply incised sternum may also preclude very strong 
forces being exerted by the pectoralis and supracoracoideus.  The low 
hemogobin count is probably due to many factors, the most obvious is 
that the "disuse" of the forelimbs (when a muscle is not used the blood 
supply to it diminishes, hence making it "white").  

<<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.>>

The large muscle attachments are indicative of strong muscles, in 
galliforms the muscle attachments are comparatively weaker than other 
birds (with the exception of Megapodidae and Quercymegapodidae).  As I 
have noted above the low hemoglobin count is due to the "disuse" of a 
body part (this counts only for bird muscles as far as I know).  What is 
seen in phorusrhacids is a rearrangements of the flight muscles that 
they inherited to a musclature that would be advantageous to a predatory 
animal.  

>PS. Where can I get a detailed article about Robert Chandler's work >on 
Titanis?

He has something coming out soon in JVP.  And he published some thing in 
a Florida museum journal (I lost the ref).

Matt Troutman

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