During the Ediacaran period (635–542 MYA), life evolved more diverse and sophisticated cell chemistry, including genetic mechanisms which would be conserved through time. At the cellular level, some organisms had novelties that straddled classification. Exotic single-celled microorganisms emerged – neither bacterial nor animal – that had features like fungi and multicellular algae. The Ediacaran was a period of fundamental experimentation in life form.
Complex animals got their start millions of years before the Cambrian, during the Ediacaran. ~ American paleontologist Rachel Wood
Life forms were microscopic prior to the Ediacaran. That changed as size became a way to spread.