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This activity entails a basic morphometrics lab, followed up by an in-class exercise to reinforce some of the same key concepts. The lab exercise familiarizes the student with basic methods of quantitative characterization and statistical comparison through measurement of pygidia (tails) of two species of the Ordovician trilobite Bellefontia â one from New York and one from Pennsylvania. Actual specimens, while nice, are not required; data acquired by measurement from photo collages will suffice. The exercise culminates in a statistical test of significance (using the Z-statistic) of the difference in slopes of the lines acquired for data from the two species. The data also serve to pose questions and prompt consideration of growth trajectories and discrimination of isometric from anisometric growth. The in-class activity builds on the knowledge base built in the lab but applies it to species discrimination based on the cranidia (central part of the head) of three species of the Upper Cambrian genus Bartonaspis, known to be of identical age from their occurrences within the very thin (everywhere 2m or less) Irvingella major Zone of the Elvinia trilobite Zone. The importance of that subzone, which is the "critical interval" at the top of the Pterocephaliid Biomere the basal unit of the Sunwaptan Stage traceable throughout Laurentian North America, also contributes to the significance of the exercise. With the insight developed from the lab, students are able to confidently distinguish the three species of Bartonaspis (from three photo collages), but must thoughtfully evaluate the data presented in bivariate plots of cranidial morphologic data to do so. The exercise gives the students a good sense of the level of familiarity and morphologic characterization necessary to do species-level identification, and also some worthwhile practice in basic quantitative methods.
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