Sarah Fowell

University of Alaska Fairbanks

Required undergraduate course in paleobiology

My students complete this exercise after they have been introduced to cladistic analysis and related terminology (e.g. synapomorphy and symplesiomorphy). However, this activity could also be used to introduce a unit on cladistics.

This activity precedes a series of homework exercises in which students design cladograms to depict the relationships between three or four taxa.

sister groups
symplesiomorphies
synapomorphies
outgroup

I originally designed this exercise to allow students to explore the answer to a question that never fails to arise as students learn the "rules" of cladistic analysis: "Why do we exclude primitive features?" It also gives my invertebrate paleontology students a chance to practice making a cladogram using a group with which they are typically more familiar (chordates!).

Formulating a hypothesis regarding evolutionary relationships and depicting it on a cladogram
Justifying the hypothesis by adding synapomorphies to the cladogram
Distinguishing shared derived characters from shared primitive characters

The first page of the presentation includes photos of 12 animals. I print this page, cut up the photos, and give a set of photos to each group of students. Working in groups of 2 or 3, the students spend ~10 minutes arranging the photos to depict the evolutionary relationships among the animals. This exercise is followed by 4 clicker questions about relationships that students commonly misconstrue due to convergence or shared primitive features. I use the clicker questions to initiate class discussion of group results. Then we discuss the evidence (anatomy, biochemistry) for current thinking about these relationships. Once we have established a consensus, students are asked to place pictures of a subset of the animals at the tips of the branches on a pre-designed cladogram. The activity gives me insight into students' preconceptions regarding vertebrate phylogeny, encourages students to identify their own misconceptions, promotes peer instruction and highlights problems associated with determining relationships based on shared primitive features. Placing the animals on a pre-designed cladogram allows students to translate their hypothesis about relationships into a visual diagram, an exercise that I hope will help students to extract the phylogenetic hypotheses depicted on cladograms in papers and textbooks. Once we have established a consensus cladogram, students must go one step further and add evidence (synapomorphies) to their cladograms. Students spend ~ 10 minutes brainstorming with their group to place synapormorphies at each node of the diagram. An example is provided for whales and hippos, groups for which the evidence of shared ancestry is difficult to recognize based on the anatomy of living specimens. After adding synapomorphies to their diagrams, students will work together as a class, contributing shared derived features to a group cladogram. If time permits, it would also be possible to complete the exercise with a gallery walk, where each group posts a copy of their cladogram + synapomorphies on the wall for other groups to examine and edit.

This is not a scored exercise. I collect the final cladogram to determine whether students have correctly translated their hypothesis onto the diagram. Students receive feedback on their cladograms.