The period early in the Cambrian period (535 - 525 million years ago) when many phyla of living animals appear suddenly.
- Fossils of three living animal phyla appear suddenly:
- Cnidaria (sea anemones and their relatives)
- Porifera (sponges)
- Mollusca (molluscs)
Prior to the Cambrian explosion, all large animals were soft-bodied with little evidence of predation.
In a short period of time (10 years), predators over 1m in lengths emerged that had claws and other features for capturing prey; simultaneously, new defensive adaptations, such as sharp spines and heavy body armor appears in their prey.