In which historical period did Japanese funeral customs begin?

Funeral custom began in primitive Japan. There is a record in the Japanese history book "Ancient Stories" that "the boy in the sky died, singing and dancing for eight days and eight nights", which reflects the situation of Japanese primitive ancestors singing and dancing when they died. After death, there is no hurry to be buried. First, several women sang and danced in front of the body, and beat the pestle and rice before burial.