Ans

1. Chapter 33 Comparing Chordates
Observing Vertebrate Skeletons
Introduction
The body plans of all vertebrates are similar in some ways. One
characteristic shared by all vertebrates is the presence of a skeleton.
The skeleton of a vertebrate is an endoskeleton, or internal skeleton.
It is made up, in part, of living cells and thus is able to grow. It is not
shed as are many exoskeletons. The endoskeleton provides support,
protects the internal organs, and is a site for the attachment of muscles.
Skeletal similarities are evidence that these different animals have
evolved from a common ancestor. Structures such as bones that have a
common origin but different function are called homologous
structures.
In this investigation, you will compare the skeletons of several
different vertebrates and look for evidence of homologous structures.
You will also classify unknown bone specimens.
Problem
What are the similarities and differences among vertebrate skeletons?
What homologous structures can be identified on these skeletons?
Pre-Lab Discussion
Read the entire investigation. Then, work with a partner to answer
the following questions.
1. What will you be comparing in this investigation?
The skeletons of a human, a frog, a crocodile, a pigeon, a cat, and an unknown animal.
2. What do the animals you will be studying in this investigation all
have in common?
They are all vertebrates.
3. What evidence will you be looking for to demonstrate that
vertebrates share a common ancestor?
The presence of homologous structures
4. Based on the investigation title and the other animals you will be
studying in this investigation, from what group of animals will the
mystery bones come?
The mystery bones are part of a vertebrate.
5. How will you determine which parts of the skeleton the mystery
bones come from?
By comparing them to the bones in the skeletons that are illustrated
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Name______________________________ Class__________________ Date ______________
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You may want to refer students to
Section 33–3 in the textbook before
performing this investigation.
Time required: 45 minutes
If actual skeletons or models are available, they should be used in conjunction with this
investigation. Vertebrate skeletons can be obtained from a biological supply house.

2. Materials (per group)
set of “mystery” bones
Procedure
1. Carefully examine the labeled human skeleton in Figure 1. The
human skeleton contains more than 200 bones. Become familiar
with the names and structures of the bones in Figure 1.
Human Skeleton
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Ribs
Sternum
Humerus
Radius
Ulna
Carpals
Metacarpals
Phalanges
Femur
Patella
Fibula
Tibia
Tarsals
Metatarsals
Phalanges
Scapula
Vertebrae
PELVIC
GIRDLE
Ilium
Cranium
SKULL
Maxilla
Mandible
Clavicle PECTORAL
GIRDLE
HAND
FOOT
Pubis
Ischium
Figure 1
The “mystery” bones can be made by boiling a chicken and removing the meat
from the bones. For a more challenging problem, you can obtain pig, lamb,
or cattle bones from a butcher or grocery store; cook the bones to destroy
pathogens. Each group should be given several bones from the same type of
animal to identify.

3. 2. Look at the frog skeleton in Figure 2. As you examine the skeleton,
compare it to the human skeleton in Figure 1. Label the bones of the
frog skeleton using the names from Figure 1.
3. Repeat step 2 with the skeletons of the crocodile, pigeon, and cat in
Figures 3, 4, and 5.
4. Obtain a set of “mystery” bones from your teacher. Identify the
bones by comparing them to the bones of each skeleton observed in
this investigation. Wash your hands with soap and warm water
before leaving the lab.
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PELVIC GIRDLE
Femur
Sternum
Vertebrae
Pectoral girdle
Humerus
HAND
Radio-ulna
SKULL
Tibio-fibula
Tarsus
FOOT
Metatarsus
Phalanges
SKULL
Scapula Vertebrae
Ulna Tibia
FOOT
Fibula
Femur
HAND
Radius
Humerus
Frog Skeleton
Figure 2
Crocodile Skeleton
Figure 3

4. 218 Biology Laboratory Manual B/Chapter 33
©Prentice-Hall,Inc.
Ulna
Humerus
ScapulaRadius
SKULL
Cranium
Mandible
Vertebrae
Clavicle
Sternum
Patella
Fibula
Femur
HAND
Tibia FOOT
PELVIC GIRDLE
Pigeon Skeleton
Figure 4
KULL
Cranium
Vertebrae
Scapula
Ribs
Femur
PELVIC
GIRDLE
Mandible
Humerus
Radius
HAND Ulna
Patella
Tibia
Fibula
FOOT
Cat Skeleton
Figure 5

5. Analysis and Conclusions
1.Comparing and Contrasting What are three characteristics that all
of the skeletons share?
Answers may include a bony skeleton, four limbs, a skull, presence of vertebrae in the backbone,
jaws, and an internal skeleton.
2.Comparing and Contrasting What are three differences that exist
among the skeletons?
Answers may include number of bones, presence of a tail, shape of bones, overall size, and type of teeth.
3.Drawing Conclusions How do the functions of the forelimbs differ
among the five vertebrates you have examined?
The forelimbs of humans are used for grasping objects, the forelimbs of frogs are used in landing after a jump,
the forelimbs of pigeons are used for flying, and the forelimbs of crocodiles and cats are used for walking.
4.Analyzing Data What type of evidence would indicate that
the human hand, pigeon wing, and cat paw are homologous
structures?
These structures contain bones of similar shape, number, and arrangement.
5.Classifying Which of the skeletons is most closely related to the
human skeleton? What evidence supports your answer?
With the exception of the tail, the backbones of humans and cats are most alike in the number and
arrangement of vertebrae.
6.Classifying To what type of animal do you think your “mystery”
bones belong? On what evidence do you base your conclusion?
Answers will depend on the unknown skeleton bones provided. If chicken bones are used, students may
recognize the flat sternum and the fused metacarpals.
7.Drawing Conclusions Are bones that are similar in structure
always similar in function? Give an example to defend
your answer.
No. While the forearms of cats and humans are similar in structure, the cat generally uses its forearms for
walking, and the human uses its forearms for grasping objects.
8.Drawing Conclusions What evidence have you obtained in this
investigation to support the theory that vertebrates evolved from
a common ancestor?
All of the vertebrates examined in this investigation had homologous structures within their skeletons.
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6. 9.Comparing and Contrasting How do the bones in the limbs of the
frog differ from those in the other four skeletons?
The frog has only one bone in the forearm (radio-ulna) and one bone in the lower leg (tibia-fibula).
10.Observing Describe the “mystery” bones in your collection.
Answers will depend on the bones provided.
11.Drawing Conclusions To what parts of the skeleton do your
“mystery” bones belong?
Answers will depend on the bones provided.
Going Further
Using reference materials, find examples of other vertebrate skeletons.
How are these skeletons similar to and different from those you have
studied in this investigation? How are the skeletons of these other
vertebrates adapted to the environments in which they live?
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