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.