Theories: Change in Rates of Evolution

About 565 million years ago complex traces and large complex Ediacaran creatures appeared. About 525 million years ago, the Burgess shale fauna appeared in the fossil record.

That is just 40 million years for the ancestors of all living and many extinct phyla of multicellular creatures to evolve. For a relatively short time the rate of evolution was very fast.

As of now, there are theories as to why there was such a drastic short-term increase in the rate of evolution, but no answers.