Cladogram Construction and Vertebrate Phylogeny
University of Alaska Fairbanks
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This page first made public: May 21, 2009
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Students are given pictures of a variety of extant vertebrates. They work in groups to determine which animals are most closely related. Following a series of clicker questions and a discussion of the relationships, they place a subset of the animals on a cladogram. Finally, students add synapomorphies to the cladogram in order to justify their hypotheis.
Required undergraduate course in paleobiology
Skills and concepts that students must have mastered
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.
How the activity is situated in the course
This activity precedes a series of homework exercises in which students design cladograms to depict the relationships between three or four taxa.
Content/concepts goals for this activity
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!).
Higher order thinking skills goals for this activity
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
Other skills goals for this activity
Description of the activity/assignment
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.
Determining whether students have met the goals
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.
More information about assessment tools and techniques.
Download teaching materials and tips
Activity Description/Assignment:Cladogram Construction (PowerPoint 1.3MB Aug2 09)