Complex sentence: During the late Eocene, the Australian/New Guinean continent began a period of drying that caused a retreat in the area of rainforest, which forced the ancestral pademelons to begin living in a dryer, rockier environment.
Split into simpler sentences: During the late Eocene the Australian/New Guinean continent began a period of drying that caused a retreat in the area of rainforest. The retreat of the rainforest forced the ancestral pademelons to begin living in a dryer, rockier environment.