Review Questions for Biology 404

HOL Ch. 15: Origin of Mammals

1. What significance does the masseter muscle of mammals have? How does Thrinaxodon (Fig. 15.1) compare with mammals with respect to its jaw? Explain how the articulation of the jaw (i.e., the joint) differs in reptiles and mammals. How do the teeth compare?

2. Why is hearing related to the changes in the jaw in question 1 above?

3. Compare a reptile, Thrinaxodon, and a typical mammal with respect to stance, locomotion, rib cage, and breathing, and be able to explain how these features are all related.

4. What is Charles Darwin's hypothesis of how suckling evolved in mammals? What is viviparity? How are monotremes, marsupials, and placentals different with respect to birth of their offspring?

5. Describe the earliest known mammal, Morganucodon. When did it live? What was its size, morphology, and ecology? What were its teeth like? (See Fig. 15.6.) What were the kuehneotherids and the multituberculates? What is the significance of Tribotherium?

6. Why was the oldest monotreme fossil threatened when it was found? What evidence supports the hypothesis that we are more closely related to the extinct multituberculates than we are to the still-living platypus (which is certainly not a "primitive" mammal in many respects)?

7. What is the trophoblast in marsupials? Do placental mammals have it? What are the advantages and disadvantages of a placenta? How do thermoregulation and metabolic rate differ in marsupials and placentals?

8. Did mammals outcompete the dinosaurs?

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