1. National Geographic, Nov. 2001

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

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

4. CLUE # ~36 mya
Dorudon 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.

5. Extinct land mammals with whale-like teeth
CLUE # ~55 mya
Mesonychlids
Extinct land mammals with whale-like teeth

6. Areas in red indicate sites where fossil whales have been found.

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

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

9. Basilosaurus Hind leg found by Gingerich in Egypt, 1990
CLUE # ~37 mya
Basilosaurus Hind leg found by Gingerich in Egypt, 1990
Philip Gingerich

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

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

12. Hans Thewissen with colleague Ellen Williams

13. 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”.

14. Ambulocetus

15. CLUE # 7 Between 1983 and 1997 DNA and protein “finger printing” studies indicate artiodactyls such as deer, pigs, cattle, and hippos are closely related to whales.
Artiodactyls are mammals with an even number (2 or 4) of toes

16. Hippos
How many toes can you count in these artiodactyls?

17. CLUE #8 ~47 mya
Rodhocetus and Artiocetus In 2001 in Pakistan Gingerich finds important new whale fossils that include leg and foot bones. What question might the foot bones answer?

18. 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?

19. Astragalus Ankle Bones (in circles)
Rodhocetus
Astragalus Ankle Bones (in circles)
Artiocetus
Rodhocetus

20. Comparison of Ankle Bones
astragali above
calcanei below
Primitive whales
Mesonychians
Artiodactyls

21. Fossil Hind Limb of Rodhocetus Showing Ankle Bones
1 Fossil Mesonychid astragalus 2 Modern artiodactyl astragalus Fossil Rodhocetus astragalus

22. FAMILY TREE OF CETACEANS shows the descent of modern odontocetes and mysticetes from extinct ancestors

23. Branching diagrams illustrate various hypotheses of the relationship of whales to other mammals
Hippos = Hippopotamids Mesos = Mesonychids Artios = Artiodactyls other than hippos

24. 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

25. 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

26. 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