Several different hypotheses attempt to explain the sudden appearance of animal diversity during the Cambrian Explosion. One suggests that oxygen levels prior to the Cambrian Explosion may have been too low to support the metabolism of larger and more active animals. Rising oxygen levels must have led to this sudden burst in in animal life and diversity, in which animals with higher metabolic rates and larger bodies were able to survive and flourish. Another theory is that the explosion of animal diversity was driven by the emergence of predator and prey relationships. Once predators started to evolve new mechanisms to track down prey, huge selection pressures forced prey to evolve better defenses, which further encouraged predators to adapt
