MYSTICETES (baleen whales) above ODONTOCETES (toothed whales) below

2. MYSTICETES (baleen whales) above ODONTOCETES (toothed whales) below What are the characteristics of modern whales?

3. How do we know that whales have evolved? Fossil evidence, which includes: 1) Whale ancestors with major structures that are homologous to tetrapods. So what does a “homologous structure” mean? Homologous structures are characteristics which are shared by related species because they have been inherited in some way from a common ancestor.

4. Vertebrate Forelimb Homologies What pattern shows that they came from a common ancestor?

5. 2) Evidence in LIVING WHALES of vestigial structures related to their ancestry. What is a vestigial structure? A structure or organ is vestigial if it has diminished in size or usefulness in the course of evolution. Such features, though no longer useful (as far as we can tell), are presumed to have been useful in ancestral species.

6. Areas in red indicate sites where fossil whales have been found. How does this relate to Geologic Uniformitarianism?

7. The shallow Tethys Sea is the likely site of early whale evolution

8. MYSTICETES – Modern Baleen Whales What is this structure? Is it functional? What does the presence of this structure tell us about whale evolution?

9. Dorudon~36 mya Scientists have found many fossils of primitive whales like Dorudon dated between 25 and 45 mya. No modern whales have been found in this time period.

10. Basilosaurus ~37 mya Hind leg found by Gingerich in Egypt, 1990

11. Rodhocetus kasrani ~46 mya Found by Gingerich in 1993. Has well-developed hip bones and large pelvis. No limb bones found. Vertebrae suggest strong tail muscles and flukes for swimming.

12. Rodhocetus and Artiocetus ~47 mya In 2001 in Pakistan Gingerich finds important new whale fossils that include leg and foot bones. What question might the foot bones answer?

13. September 2001 The journal Science publishes whale evolution articles by Gingerich, Theweissen, and Kenneth Rose. Rodhocetus Look closely. What do you see in this artist’s depiction of Rodhocetus?

14. ~48 mya Ambulocetus Found by Hans Thweissen in Pakistan in 1994. Fossil has teeth similar to Mesonychids and early whales. Each toe on the on the huge hind feet has a tiny hoof.

15. Ambulocetus natans - The 49-million year old walking, swimming whale had long hind and front legs, but had teeth and ears like more modern whales. Hans Thewissen (pictured) says the whale “was on the fence between land and sea”.

16. Ambulocetus

17. Pakicetus~50 mya Skull and teeth only Found by Philip Gingerich in Pakistan, 1983

19. Mesonychlids ~55 mya Extinct land mammals with whale-like teeth

20. LOSING THEIR LEGS Four-legged Ambulocetus (~48 mya) could walk and swim Basilosaurus (~37 mya) had reduced but well-developed hind limbs Today’s sperm whale has vestigial hind limbs

21. NASAL DRIFT Pakicetus (~50 mya) had a land mammal’s nostrils at end of the snout Rodhocetus (~47 mya) swam the seas with nostrils intermediate between those of its ancestors and modern whales A modern gray whale’s blowhole is at the top of its head

22. HEARING AIDS Ambulocetus (~48 mya) heard directly through its ears In Basilosaurus (~37 mya) sounds were transmitted to middle ears as vibrations from lower jaw In modern toothed whales the melon directs sound at an object, and the lower jaw receives echoing reply