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Re: A question concerning the BCF hypothesis



In a message dated 2/25/01 10:36:42 AM EST, henri.ronkko@kolumbus.fi writes:

<< "A sprawling diapsid such as Mesenosaurus effectively becomes an upright 
animal when climbing a tree and will suffer a momentary disadvantage until 
its blood pressure is able to partly compensate for the change. Any 
adaptation, such as a four-chambered heart, that removes this disadvantage 
will enable the animal to climb faster and easier and escape from a predator 
more effectively."
 
 Why should an erect stance be an adaptation to arboreal life? There are 
many, many climbing lizards today and I think all of them sprawl. Well, there 
are chameleons, but then again, they have the usual heart.
 
 I don't think the logic here is good at all, really. Is this really how the 
BCF goes? >>

No. Evolution of a four-chambered heart would represent an >improvement< to 
an arboreal animal but is certainly not a >prerequisite< for arboreality. It 
would also represent an improvement to a terrestrial animal, however. 
Separation of pulmonary circulation from systemic circulation seems to have 
been a good thing all around. Probably more important to the evolution of 
dinosaurs and birds than endothermy, for example.