This is very interesting.
Just read a very good book on the Cambrian Explosion by Erwin and Valentine and it delves into Ediacaran and Cryogenian evidence for multicellular life.
It also looks at genetic and biochemical environmental changes which may have allowed life to diversify-including changing O2 and carbon levels and Redox changes in biofilms with phosphate and iron reactions.
Certainly molecular clocks hint at a number of shared genes which have the basics for complex life going way back into 700MA territory.
There are a number of simple microbes today that still have the genes for bilateral symmetry and triploblastic development including basic muscle and nerve tissue- this is hints at a common ancestor to all way before the Cambrian explosion of body plans/crown phyla. There are suggestions that some species actually simplify body plans and turn off genes to evolve more adaptability to niche environments.
Some of the deep biology was a bit intricate but it's a damn good read and nicely illustrated with fossils and art work.
Graz