Systematics of some enigmatic "fossils"

Allison Tumarkin-Deratzian
Temple University
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Students and instructor work through a guided exercise to construct a character matrix and cladograms describing relationships between different types of paper clips. Students then break into small groups to complete a related exercise with a larger set of different types of pasta.

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Designed for an intermediate (2000-level) combined course in paleontology and stratigraphy for undergraduate geology/environmental science majors. The course has traditionally had no prerequisites within the major, but assumed students had taken either a general education course within the department or introductory physical geology. Prerequisites have recently been updated to include an intermediate-level facies models course.

Skills and concepts that students must have mastered

Students have already been introduced to basic structure and interpretation of cladograms and key concepts essential for cladistic analysis (shared derived characters, principle of parsimony, outgroups and character polarities). Students are also familiar with sources and types of intraspecific morphological variation (e.g. ontogenetic change, sexual dimorphism).

How the activity is situated in the course

Currently this exercise is done during the first lab period of the semester, following a lecture that introduces basic principles of taxonomy, systematics, and phylogenetic reconstruction. Discussion of the results from analysis of the pasta data sets occurs during the following week's lab period.


Content/concepts goals for this activity

Phylogenetic analysis, cladistics, character definition and coding, convergent evolution, parsimony analysis, morphological species concept, sources of intraspecific variation

Higher order thinking skills goals for this activity

Comparison of different outcomes derived from different interpretations of the same data set

Other skills goals for this activity

Group work and active class participation

Description of the activity/assignment

Students are given sets of different shaped fasteners (staples, paper clips, tacks, etc.) and work with the instructor through a guided exercise in which they construct a character matrix and cladogram depicting the phylogeny of the "organisms". Students are then divided into small groups; each group receives a set of various shapes/colors of pasta. (The sets are all the same.) Each group must decide how many species are present in their sample (considering the potential for ontogenetic and sexual variation within species), choose and define characters for a cladistic analysis, and construct a character matrix. The instructor runs the matrices through cladistic analysis software, and the following week the students receive the results from analysis of each group's data. The class then discusses the effects of species definition, character choice, etc. on phylogenetic hypotheses. The activity allows students to directly confront issues of identifying and distinguishing morphological species. Conflicting results obtained by different groups analyzing the same data set drive home the complicated nature of character choice and definition in construction of a character matrix for cladistic analysis, and underscore the fact that individual cladograms represent phylogenetic hypotheses subject to modification by further analysis. (This last point becomes necessary background as students encounter different/competing hypotheses of phylogenetic relationships during study of fossil invertebrates.)

Determining whether students have met the goals

Students turn in the written results of the paperclip exercise and each group turns in the character definitions and matrices from the pasta exercise. Evaluation is largely based on participation in the activity and follow-up discussions, as this is more an exercise in experiential learning than an assignment with correct or incorrect answers.

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