1. What were whales like 40 million years ago?

2. Indohyus

3. Pakicetus

4. Ambulocetus

5. Rhodocetus

6. Protocetus

7. Blue whale (Balenoptera musculus)

8. But how do we know?

9. Evolution of Cetaceans
Name comes from “Cetus” the seamonster in Greek mythology
Evolved from a predator on land 40 million years ago
Special adaptations:
Lack of external hind limbs
Streamlined shape and tail
Fluid filled jaw for hearing
Echolocation (in toothed cetaceans only)
Baleen for feeding (in baleen cetaceans only)

10. How do we know they were once land mammals?
1. Skeletal structure
They have the same bones in their flippers as we have in our hand
Their tails move in a horizontal motion like land mammals’ tail bones

11. Gray Whale skeleton

12. Evolution of Echolocation

13. Blowhole evolution

14. 2. Vestigial structures Hip and leg bones
(Structures that once served a purpose but no longer do)
Hip and leg bones

17. Vestigial hind limbs on a living bottlenose dolphin

18. 3. Embryological relationships - vestigial structures that occur during development of the fetus Human fetus 

19. Spotted dolphin fetus

20. 4. DNA Similarities
Cetaceans show much greater similarities in their DNA to land mammals (e.g. the hippo) than to fish or other aquatic animals