Name: ____________________________________________________________ Date: ________ Period: _____
HOMOLOGOUS STRUCTURES WORKSHEET
Directions: The diagram below shows the forelimbs of different animals. Use the diagram and the
Vertebrate Fact Sheet to answer the following questions.
1. How many bones make up the arm of a human? _____
2. Compare the human upper limb with the forelimbs of the lion, the bat and the whale. Record your
observations in the space below.
3. Which of the animals shown in the diagram has a forelimb most like the human arm? Describe the
observations that lead you to this conclusion.
All of the animals shown in the diagrams are vertebrates.
4. What is a vertebrate?
5. List some characteristics – other than the structure of their forelimb – that vertebrates share.
6. Compare the human to the animal with the most similar forelimb (see your answer to question 3). What
specific characteristics do these two animals share that the others do not.
7. Darwin and other scientists looked at the bone structure of vertebrate animals, along with other
characteristics, and inferred that all of these animals had shared a common ancestor. Write a short
paragraph that describes the evidence Darwin used to come to this conclusion?
Vertebrate Fact Sheet
Vertebrates are animals with an internal backbone or spinal column. There are over 85,000
species of vertebrate animals such as amphibians, birds, fish, mammals and reptiles. Most
large land animals are vertebrates. Even large sea animals, such as the whale, are vertebrates.
However, only about 5% of all animal species are vertebrates. The remaining 95% of animals
are invertebrates that don’t have an internal backbone (e.g., insects, mollusks and
arthropods).
The defining characteristic of all vertebrates is the vertebral column or backbone. This
vertebral column is a strong series of bones extending through the core of the body. Near the
front end of the backbone is the mouth, with the anus opening near the back end of the
backbone. In vertebrates with a tail, the vertebral column extends beyond the anus to the end
of the tail. Above the backbone is the spinal cord, a major component of the nervous system.
Below the backbone is the gastrointestinal or digestive tract.
The vertebral column is made up of many individual vertebrae interconnected with
intervertebral discs. These vertebrae and intervertebral discs provide for flexibility and
movement of the spine.