(13 pages) This activity includes a dichotomous key exercise, as well as materials for 16 station cards. Six different common Ordovician fossils are studied, and each station card contains four images of these Ordovician fossils. We have students work cooperatively (pairs) to identify the fossils shown on each station card. They work from one station to the next. By the time they have completed all stations, students will have developed a critical eye for subtle differences between the fossils. In addition, they will have become familiar and fluent with the fossil names. We use this as a practice activity, and post answers for students to check as they go. No grades are taken.