New genes appeared in many different organisms through a mechanism that has not been identified. These are associated with new body plans.
Several duplications of the homeotic genes that control major characteristics in body plans apparently arose about 540 million years ago, creating new body plans and appendage configurations.
Many mutations accumulated due to high exposure to UV radiation, creating many new kinds of organisms.
Reproductive isolation was nearly nonexistent; many "species" interbred to form hybrids that went on to become new species.