Answer:

eocene

Answer	Crossword Clue
EOCENE	Epoch when modern mammals arose
EOCENE	Period of great climate change
EOCENE	Epoch characterized by the rise of mammals

EOCENE	Epoch when horses first appeared
EOCENE	Epoch when mammals arose
EOCENE	Epoch when bats first appeared
EOCENE	Epoch in which mammals arose
EOCENE	Dawn-of-mammals epoch
EOCENE	Epoch 50 million years ago
EOCENE	Epoch of the Tertiary period
EOCENE	Epoch of 50 million years ago

EOCENE	Occurring 40 to 55 million years ago
EOCENE	Epoch in which mammals became dominant
EOCENE	Tertiary Period part
EOCENE	Epoch in which mamals arose
EOCENE	Epoch in the Cenozoic Era
EOCENE	Tertiary Period epoch