Complex sentence: Since the late Eocene, about 40 million years ago, cetaceans populated the subtropical oceans of the world and had no connection to land anymore, such as the long "Basilosaurus", sometimes referred to as "Zeuglodon".
Split into simpler sentences: Since the late Eocene, about 40 million years ago, cetaceans populated the subtropical oceans of the world and no longer had any connection to land. An example is the long "Basilosaurus", sometimes referred to as "Zeuglodon".