Horse Evolution Author: Sharon Janulaw

Overview: In this lesson the teacher describes horse evolution using illustrations of horse ancestors and modern horses.

Lesson Concepts:

• Life forms have changed over time.

Grade Span: K–2

Materials:

• Illustrations of horse ancestors and modern horses (HTML or pdf). You can also copy them from almost any biology textbook or from this site: members.tripod.com/cavanaughc/id94.htm (Note: This site has useful illustrations, but the accuracy of the text may be problematic.)

Advance Preparation:

— Read some information about horse evolution so you can tell a reasonable story.
— Prepare illustrations of horse ancestors and modern horses.

Time: 30 minutes

Grouping: Whole class

Teacher Background:

Horses evolved from small browsing animals, with four toes on each front foot and three on the rear, to the modern horse (including horses, donkeys and zebras), which are grazing animals with one toe on each foot. Characteristics, such as single toes, larger size, and modified teeth are all apparently adaptations to running fast on grassy plains and eating grasses instead of browsing on shrubs. This url, chem.tufts.edu/science/evolution/HorseEvolution.htm, gives an excellent account of up-to-date information about horse evolution. Note that examples of horse “ancestors” in textbooks are not necessarily in the direct line that led to modern horses. Some are cousins of horse ancestors. Nevertheless, these fossils illustrate transitional forms that can reasonably represent the actual horse lineage.

Teacher Resources:
— Useful for illustrations of horses: members.tripod.com/cavanaughc/id94.htm
— Information about horse evolution: chem.tufts.edu/science/evolution/HorseEvolution.htm

Teaching Tips:

Children will not grasp the vast expanses of time required for the story you tell them, but they can get the idea that types living things can change over time. The idea is that horses’ ancestors did not look or act exactly the way horses do today.

Vocabulary: browsing, grazing, hoof

Procedure:

1. Show the Picture of Hyracotherium (eohippus) and ask them to tell something they notice.
2. Tell the students that this little animal is what horses looked like 55 million years ago. They had four toes on each front foot and three on each rear foot. They stood about as high as a student’s knee and lived in the forest, eating leaves from bushes. Have students stand up and hold one hand flat (horizontally) at knee level. Ask them to show with their other hand how tall they think horses are today. Then show them with your hand.
3. Present, in turn, each of the illustrated stages of horse evolution. As you go, ask them to observe and tell the differences they notice. Tell them that the ancestors of modern horses got bigger and changed in other ways. They lost toes, ending up with only one on each foot, and their teeth became better adapted to eating grass. All the horses of today are large and live on open plains, eating mostly grasses.
4. Place the horse ancestors and modern horses in a line on the wall (or on a timeline) so students can look at them occasionally. As you place them in a line, briefly review the changes that occurred over time. This will aid in absorption of the idea of change over time.