Biology 11
Evolution of the Vertebrates
Read pages 785-798 and answer the following questions
1. When did the vertebrates first evolve? More than 500 million years ago
2. Write the correct order of evolution of the following (according to the text):
2 Amphibians
4 Birds
4 Mammals
1 Lobe finned fish
3 Reptiles
3. What situations tend to cause divergent evolution to occur in mammals? If closely related evolutionary
lines are subjected to different forces of natural selection they tend to become more dissimilar as they
evolve.
4. What situations tend to cause convergent evolution to occur in mammals? If evolutionary lines encounter
extremely similar forces of natural selectin they tend to become more similar to one another.
5. Why is the ability to control temperature such an advantage in the struggle for existence? Many chemical
reactions essential to life functions occur work better at certain temperatures. These chemical reactions
run smoother when an animal’s temperature remains within a preferred range.
6. What is a general trend in the evolution of the organ systems of vertebrates? As you move through the
vertebrate groups the organ systems tend to become increasingly complex.
7. What are two trends that occur in the limbs and vertebral column in the evolution from amphibians to
mammals? First, the position of thelimbs relative to the body shifts toward the centre and secondly the
movement of the vertebral column when the animal runs changes from a side-to-side motion to and upand-down motion.
8. With what types of feeding are these skulls associated?
Hummingbird
To feed on nectar
Includes long tongue
sip nectar
Baleen whale
Filter feeding
sieve like structures
to strain food
Leopard
Sharp mouthparts to
tear meat from body
of prey
9. What increases (to improve the efficiency of gas exchange) as lungs evolve? Large chambers are divided
into smaller chambers increasing the surface area available for gas exchange.
Biology 11
10. Define:
a) Single loop circulatory system. A blood system in which blood travels from the heart to the
gills to the body and back in a single loop.
b) Double loop circulatory system A blood system in which blood vessels first carry blood from
the heart to the lungs and then back to the heart in the first loop then the blood is carried from the heart to
the body and back to the heart in a second loop.
11. How can we see the first step toward developing a second loop circulatory system? In lungfish blood from
the lungs has a direct connection back to the heart and there are partial partitions in the atrium and
ventricle.
12. Fill in the diagrams of these hearts.
Lungs
Body
13. Which animals have two atria in their hearts?
Frogs, reptiles, birds, and mammals
14. Which animals have four chambers in their hearts?
Crocodilian reptiles, birds and mammals
15. What does partitioning the heart into four chambers allow for?
Separation of oxygenated and deoxygenated blood
16. What structures are important in excretion in fish? Gills
17. What organs are used for cleaning the blood of land vertebrates? Kidneys
18. Explain why aquatic animals can eliminate wastes in the form of ammonia, whereas land animals cannot.
Aquatic animals don’t lose water through osmosis like land animals do. Urea is less toxic than ammonia
and can be concentrated (thereby keeping more water in the body).
19. What is ammonia changed into in
a) reptiles and birds? Uric acid
b) cartilaginous fishes, terrestrial amphibians and mammals? Urea
20. What happens to the cerebrum as you move up the classes of vertebrates? The size and complexity of the
cerebrum increases as you move thorough the vertebrate classes.
Biology 11
21. How do vertebrates reproduce? They reproduce sexually
22. Which animals tend to have external fertilization and which tend to have internal fertilization?
Codfish and frogs have external fertilization, while reptiles, birds mammals cartilaginous fishes and certain
amphibians reproduce via internal fertilization.
23. Define:
a ) oviparous -eggs develop outside the mother’s body
b) ovoviviparous – eggs develop inside the mother’s body but the embryos receive the nutrients
they need from the yolk that surrounds them not from the mother directly
c) viviparous – the developing embryo obtains nutrients directly from the mother’s body