Mammalian Locomotion & Habitat Adaptation

Mammals: Locomotion & Aquatic Habitats

• Mammals have reinvaded the sea 7 times, with 5 lineages still extant.
  • Cetacea (whales, dolphins, porpoises): Evolved in the Early Eocene (56 to 34 mya).
  • Sirenia (manatees, dugongs): Evolved in the Early Eocene.
  • Pinnipedia (seals, sea lions, walruses): Evolved in the Late Oligocene (34 to 23 mya).
  • Polar bear: A very recent adaptation.
  • Sea otter: A very recent adaptation.
    • Note: Polar bears and sea otters retain terrestrial forms but spend a great deal of time in water.

Marine Habitats and Adaptations

• Initial adaptations involved feeding in water.
• Eocene Epoch (56 to 34 mya):
  • Cetacea and Sirenia evolved in warm, shallow, productive seas with abundant resources.
• Oligocene Epoch (34 to 23 mya):
  • Pinnipedia evolved when oceans had more dramatic temperature gradients and concentrated productivity.
• Examples of transitional fossils:
  • Puijila darwini: A potential