Possible Clues:

• Epoch that produced the earliest primate fossils
• Geological time the Executive Officer's seen, we hear
• Epoch of mammals' appearance
• Seen at last to sound an age
• Epoch when modern mammals appeared
• Epoch in which modern mammals first emerged
• Epoch 50 million years ago
• Epoch of modern birds and mammals
• In old age the one gets broken in ease, by the sound of it
• Formed in the second epoch of the Tertiary period