1. Early Cetaceans:
During the early Tertiary period, known as the Paleocene and Eocene epochs, cetaceans were transitioning from land-based mammals to fully aquatic creatures. Archaeoceti, considered the earliest whales, still retained hind limbs but had already adapted to a marine lifestyle. Some notable examples include Pakicetus, Ambulocetus, and Basilosaurus.
2. Whalebone Whales (Mysticeti):
The Miocene epoch (23 million to 5 million years ago) witnessed the emergence of baleen whales or mysticetes. These whales, characterized by the presence of baleen plates instead of teeth, thrived in various oceanic environments. Some well-known mysticetes from the Tertiary period include Balaenoptera (blue whales, fin whales), Eschrichtius (gray whales), and Megaptera (humpback whales).
3. Toothed Whales (Odontoceti):
The Tertiary period also saw the diversification of toothed whales or odontocetes, which include dolphins, porpoises, and sperm whales. These whales relied on echolocation and specialized teeth to hunt and navigate in the vast oceans. Notable examples from this period include Kentriodon, Xenorophus, and Squalodon.
4. Geographic Distribution:
During the Tertiary period, whales inhabited a wide range of geographic locations, including the Tethys Sea, the Pacific Ocean, and the shallow seas that covered parts of modern Europe, Asia, and North America. Their distribution was influenced by factors such as food availability, climate conditions, and competition from other marine predators.
In summary, during the Tertiary period, whales underwent significant evolutionary transformations, diversifying into various groups such as baleen whales and toothed whales. They inhabited diverse oceanic environments and played crucial roles in the marine ecosystems of their time.