What is a paleontological species?
Deborah K. Anderson
St. Norbert College
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In this specimen-based activity, students study ischyromyid rodent molar cusp morphology and develop their understanding of the morphological species concept as applied in paleontology.
Introductory paleobiology course.
Skills and concepts that students must have mastered
Experience with a compound microscope, knowledge of the morphological species concept, and taxonomic hierarchy. Experience with a graphical program and basic statistics is helpful, but can also be part of the learning experience.
How the activity is situated in the course
This is one of the first laboratory exercises, it follows a lecture-discussion of species concepts.
Content/concepts goals for this activity
A constructivist approach to developing an understanding of the species concept as it applies to fossil specimens.
Higher order thinking skills goals for this activity
Pattern recognition: using common morphological elements (e.g. molar cusps, cingula, crests) to differentiate among taxa. Evaluation of the significance of variation in molar metrics within and between species.
Other skills goals for this activity
Writing: describing patterns using qualitative data. Microscope: using an optical micrometer to collect data. Data analysis: conducting basic statistical analyses (e.g. means, SD, CV), presenting data graphically using Minitab.
Description of the activity/assignment
In this two-part laboratory exercise, students explore the paleontological species concept by studying fossil rodent specimens and classifying them. This lab exercise follows a discussion of the species concept and is the first lab exercise in the course that gives students experience with fossil specimens. Part I: Students begin by studying casts of fossil mammal molars from which they construct clay models. This develops their ability to recognize the cusp pattern. Next, students are given 5 specimens that belong to a single species. First, they write qualitative descriptions of each specimen and then use an optical micrometer fitted to a microscope to collect data about molar length and width. Each group of students has a distinct species of the same rodent family, Ischyromyidae. Part II: The quantitative data is entered into a spreadsheet in Minitab, basic statistics are calculated and students plot molar length vs. width and/or molar area ln (LxW) vs. biostratigraphic level (if you want to include the time factor). (Class data is combined for the statistical analysis and graphing. An alternative approach, for a small class size, is to provide students with additional data points.) Each student pair must explain how they would classify each of the fossil specimens that they studied and the basis for their decision.
Determining whether students have met the goals
During a follow-up classroom discussion students explain what they have discovered about the morphological species concept. Students hand in their raw data, qualitative descriptions, and graphs in the form of a mini lab report. Finally, students answer questions in the next unit exam directly related to the concepts applied and/or skills developed in this exercise.
More information about assessment tools and techniques.
Teaching materials and tips
Activity Description/Assignment: What is a paleontological species student handout (Microsoft Word 31kB Aug2 09)
Enough clay for students to work individually or in groups of three to make the molar model.
A model to follow (I use large casts of rodent molars) for the clay modeling part.
Fossils and/or casts
Hand lenses or microscopes
Access to a computer and Minitab or other graphical software, possibly graph paper.
Other taxa: I recommend using a taxonomic group that you are most comfortable with and one that you have ample fossils and/or casts for the exercise.
Basic statistics: The statistics can be as simple or involved as you choose. I include the mean, standard deviation, standard error, range and CV.
Common pitfalls: Be prepared for some students to work more quickly than others. Extensions of the exercise, such as creating more graphs or looking at more specimens to increase sample size will keep these students busy.
Add time as another part of the data set.
Incorporate an investigation of intraspecific and interspecific variability.
Suggested opening to lab (one possibility):
Yesterday, we discussed several species concepts. We focused on the morphological species concept because it is often the one followed in taxonomic identification. While each of the species concepts have their merits, there are many challenges when it comes to a practical application of the definitions.
In today's lab, you will experience some of those challenges firsthand.
As a result of participating in this laboratory activity, you will be able to . . .
1. Describe the species concept as it applies to fossil specimens.
2. Use common morphological features (e.g. cusps and cingula) and metric elements (e.g. length and width of molars) to differentiate among taxa. (Interchange features to fit the type of fossil specimens you are using in the exercise.)
3. Use Minitab for basic statistical analyses and graphing.