Do you have a citation for the claim that breathing in general pre-dated heartbeat as an indication of life?

I actually did make that up based on my intuition on the matter. However I was able to find some support via google. Here is a book that claims that cold body and cessation of breath are predate cardiac criteria: Trauma: Critical Care By William C. Wilson, Christopher M. Grande, David B. Hoyt, pp. 1218

I would say that while social norms regarding what is unacceptable treatment of a corpse vary, there seems to be a prevailing theme of cultures adopting strong norms regarding such treatment. Sky burial is just one such norm. I see no reason cryonics (including neuro) could not be another.

It is interesting that the Wikipedia article claims that the Pirahã do not have a social hierarchy. Perhaps this supports my position that treatment of corpses is primarily status-related (as opposed to a method of avoiding inflicting trauma on the living).