1. Table of Contents What Is a Vertebrate? Fishes Amphibians Reptiles
Vertebrate History in Rocks

2. Ancient Jawless Fish - What Is a Vertebrate?
Look backward in time, into an ocean 530 million years ago. There you see a strange-looking creature—a jawless fish—that is about as long as your index finger.

3. Characteristics of Chordates
- What Is a Vertebrate?
Characteristics of Chordates
This lancelet shows the characteristics of a chordate: a notochord, a nerve cord down its back, and gill slits.

4. Building Vocabulary - What Is a Vertebrate?
A definition states the meaning of a word or phrase by telling about its most important feature or function. After you read the section, reread the paragraphs that contain definitions of Key Terms. Use the information you have learned to write a definition of each Key Term in your own words.
Key Terms:
Key Terms:
Examples:
ectotherm
endotherm
Examples:
chordate
An ectotherm is an animal whose body does not produce much internal heat.
All members of this phylum are called chordates.
notochord
The phylum name Chordata comes from the notochord, a flexible rod that supports a chordate’s back.
The beaver is an example of an endotherm—an animal whose body regulates its own temperature by controlling the internal heat it produces.
vertebra
You can see in Figure 2 that the backbone is formed by many similar bones called vertebrae.

5. Click the SciLinks button for links on vertebrates.
- What Is a Vertebrate?
Links on Vertebrates
Click the SciLinks button for links on vertebrates.

6. End of Section: What Is a Vertebrate?

7. Characteristics of Fishes
Most fishes obtain oxygen through gills.

8. - Fishes
Bony Fishes
A bony fish has jaws, scales, a pocket on each side of the head that holds the gills, and a skeleton made of hard bones.

9. Previewing Visuals - Fishes
Before you read, preview Figure 12. Then write two questions that you have about the diagram in a graphic organizer like the one below. As you read, answer your questions.
Structure of a Fish
Q. What is a swim bladder?
A. A swim bladder is an internal, gas-filled sac that helps stabilize the fish at different depths in the water.
Q. What is the function of the tail fin?
A. It helps provide the power for swimming.

10. End of Section: Fishes

11. What Is an Amphibian? - Amphibians
During its metamorphosis from tadpole to adult, a frog’s body changes dramatically.

12. Living on Land - Amphibians
Many adult amphibians have lungs, a heart with three chambers, and a double-loop circulatory system.

13. Sequencing - Amphibians
Make a cycle diagram like the one below that shows the different stages of a frog’s metamorphosis during its life cycle. Write each step of the process in a separate circle.
Frog Metamorphosis
Adult frog
Tail is absorbed.
Fertilized egg
Front legs develop.
Tadpole hatches.
Hind legs develop.

14. More on The Frog Life Cycle
- Amphibians
More on The Frog Life Cycle
Click the PHSchool.com button for an activity about the frog life cycle.

15. End of Section: Amphibians

16. Adaptations for Life on Land
- Reptiles
Adaptations for Life on Land
The membranes and shell of an amniotic egg protect the developing embryo.

17. Characteristics of a Lizard
- Reptiles
Characteristics of a Lizard
This lizard, a Jackson’s chameleon, has many adaptations that help
it survive in its
environment.

18. The Sex Ratio of Newly Hatched Alligators
- Reptiles
The Sex Ratio of Newly Hatched Alligators
The temperature of the developing eggs of the American alligator affects the sex ratio of the young. (Sex ratio is the number of females compared with the number of males.)

19. The Sex Ratio of Newly Hatched Alligators
- Reptiles
The Sex Ratio of Newly Hatched Alligators
Reading Graphs:
At which temperature(s) did only females hatch?
29.4ºC

20. The Sex Ratio of Newly Hatched Alligators
- Reptiles
The Sex Ratio of Newly Hatched Alligators
Drawing Conclusions:
What effect does the temperature of developing eggs have on the sex of the baby alligators?
The warmer the incubation temperature, the greater the proportion of males.

21. The Sex Ratio of Newly Hatched Alligators
- Reptiles
The Sex Ratio of Newly Hatched Alligators
Calculating:
If 100 eggs developed at 31.7ºC, about how many of the young would be male?
According to the graph, out of the 50 alligators that were incubated at 31.7ºC, about 40 (or 80%) were males. So 80% of 100 eggs (80) could be expected to hatch as males.

22. Extinct Reptiles–The Dinosaurs
Dinosaurs were the earliest vertebrates that had legs positioned directly beneath their bodies.

23. Identifying Main Ideas
- Reptiles
Identifying Main Ideas
As you read the information under the heading “Adaptations for Life on Land,” write the main idea in a graphic organizer like the one below. Then write three supporting details that further explain the main idea.
Main Idea
Reptiles are adapted to conserve water.
Detail
Detail
Detail
Reptiles have a thick, scaly skin that prevents water loss.
Reptile eggs have a shell and membranes that keep them from drying out.
A reptile’s kidneys concentrate wastes before excreting them so that little water is lost.

24. Click the PHSchool.com button for an activity about reptiles.
More on Reptiles
Click the PHSchool.com button for an activity about reptiles.

25. End of Section: Reptiles

26. Interpretation of Fossils
- Vertebrate History in Rocks
Interpretation of Fossils
Fossils most often form in layers of sedimentary rock.

27. Interpretation of Fossils
- Vertebrate History in Rocks
Interpretation of Fossils
The pattern of vertebrate evolution is branching.

28. Asking Questions - Vertebrate History in Rocks
Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions.
Questions
Answers
How do fossils form?
Fossils form from imprints or the remains of organisms.
How are fossils interpreted?
Scientists examine fossil structure and make comparisons to present-day organisms.

29. Click the SciLinks button for links on fossils.
- Vertebrate History in Rocks
Links on Fossils
Click the SciLinks button for links on fossils.

30. End of Section: Vertebrate History in Rocks

31. Graphic Organizer Main Idea
The larvae of amphibians are adapted for life in water, and adult amphibians are adapted for life on land.
Detail
Detail
Detail
Larvae have tails for swimming; adults have legs for walking.
Larvae have gills; adults have lungs.
Larvae have one-loop circulatory systems and two-chambered hearts; adults have two-loop circulatory systems and three-chambered hearts.

32. End of Section: Graphic Organizer