When God spoke to dry bones in Ezekiel 37:4, he was not talking to fresh bones that were in living people. The bones in living people like the skull, cranium, femur and fibula are still in shape.
He was talking to dry bones that were already decomposed. And so, no matter how dry, even the driest of bones which the cremated bones represent, God can speak to them and say, "... Behold I will cause breath to enter into you, and ye shall live." (Ezekiel 37:5).
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