Scholars mark the emergence of animal life as the beginning of the Fourth Epoch, the second of the two epochs in the Second Era. This Epoch is subdivided into multiple Ages, each denoting the emergence of the first types of creatures for that age. It should be noted that additional creatures of each type continue to emerge through subsequent ages and even into the present. Each Age described here is meant to note the first of those forms of life, not the last.
Unlike the Ages in the Third Era, the Era of Hominids, the six Ages of the Fourth Epoch are named rather than enumerated. Those Ages include:
- The Age of Insects
- The Age of Sea Creatures
- The Age of Worms
- The Age of Reptiles
- The Age of Megalife
- The Age of Mammals
The emergence of intelligent hominid life – humans, elves, orcs, and the like – mark the end of the Fourth Epoch and Second Era, and the beginning of the Third Era.