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"Celocanths also have a very low metabolic rate in order to conserve energy."

Thanks for jumping in. I'm not really interested in starting this up again. But in case the other guy is still listening, this is kind of argument I was looking for.

Yet in the spirit of the thread, I am forced to ask, if low metabolic rates are such an advantage we do we not see a preponderance of species with low metabolic rates?

There other species that have to conserve energy due to scarcity of nutrients and are substantially unchanged from their ancient ancestors; Crocodiles, Sharks, Tortoises and the Black Sea Sturgeon come to mind.

The relationship between slow evolution and slow metabolism is by no means conclusive on it's own so I'm not putting a great deal of emphasis on it.

Yet in the spirit of the thread, I am forced to ask, if low metabolic rates are such an advantage we do we not see a preponderance of species with low metabolic rates?

Because few creatures live in the precise type of environment that Celocanths inhabit.

Evolution does not happen in a vacuum - it is driven by environmental pressures. That's why two isolated populations of a species (for example, finches) will evolve differently - what works in one environment may not work in another.

It was mentioned that the Celocanth lives in an environment with extremely low predation. That's unusual, and might be a reason that the low metabolic rate developed. An organism in constant danger from predators is less likely to have a slow metabolic rate - it doesn't have that luxury, if you'll forgive the expression. I seem to recall that Great White sharks also have a slow metabolic rate, and they don't have much pressure from predators either. Just a guess.