Cambrian explosion

The Cambrian explosion or Cambrian radiation was the relatively short evolutionary event, beginning around in the Cambrian period, during which most major animal phyla appeared, as indicated by the fossil record. Lasting for about the next 20–25 million years, it resulted in the divergence of most modern metazoan phyla. Additionally, the event was accompanied by major diversification of other organisms. Prior to the Cambrian explosion, most organisms were simple, composed of individual cells occasionally organized into colonies. Over the following 70 to 80 million years, the rate of diversific
Ver en Wikipedia.org