What is the most significant diff. between Precambrian & Paleozoic lifeforms?!?

Answer 1

What we have evidence from in the PC is basically simple animals with entirely soft parts.

When you move into the Paleozoic, we get the Cambrian explosion, which basically is the sudden appearance of all but one of the major animal phyla. Hard parts also make their appearance, leading to a greatly more diverse fossil record, and multicellular life forms abound.

Answer 2

My guess would be the development of hard body parts that would fossilize.