Introduce students to cladistics. Point out that people trace their family history by compiling a family tree — a diagram that identifies the ancestors they are descended from and those they are related to. In a somewhat similar way, scientists use a method called cladistics to show how animals are related. Their findings are recorded in a cladogram, a type of chart. Each branching point on a cladogram represents a physical feature that evolved. For example, the feature that characterizes dinosaurs is a hole in the hip socket. All dinosaurs inherited this feature from a common ancestor — the first animal with a hole in its hip socket. Scientists may not know what this animal looked like, because they have not found fossils of every animal that ever lived. But they do know the animal had a hole in its hip socket because they can see this feature in its descendants.

Using cladistics, scientists can reconstruct an animal's family tree and show how animals are related to one another through a history of evolutionary changes. Tell students that they will examine the features of various coins to determine how they are related. This exercise will introduce them to how cladistics work. Remind students that cladistics, however, is used to determine relationships among organisms, and not necessarily objects. Have students work in small groups for this activity. You will need a penny, a nickel, a dime, and a quarter for each group. Click here to view the Using Cladistics activity sheet, then print, duplicate, and distribute. Have students complete the activity and compare their cladograms. Discuss how they arrived at their conclusions and any differences among the cladograms.