Maybe you are referring to the Ediacaran period: https://en.wikipedia.org/wiki/Ediacaran_biota https://en.wikipedia.org/wiki/Ediacaran_biota , which happened a

Maybe you are referring to the Ediacaran period: https://en.wikipedia.org/wiki/Ediacaran_biota https://en.wikipedia.org/wiki/Ediacaran_biota , which happened a bit later. Something like it can have happened before that as well, but that is more the subject of current research like in the featured article.