for by Jeffrey Scott Coker, Department of Biology, Elon University, Elon, NC Jimmie D. Agnew, Physics Department, Elon University, Elon, NC

Transcription

1 CASE TEACHING NOTES for The Story of Dinosaur Evolution by Jeffrey Scott Coker, Department of Biology, Elon University, Elon, NC Jimmie D. Agnew, Physics Department, Elon University, Elon, NC INTRODUCTION / BACKGROUND Teaching using a case study typically involves providing a story to students which they use to learn and/or make informed decisions. The Story of Dinosaur Evolution is unique in that it explores a reverse pedagogical strategy by providing students with information and then having them write their own stories. This case was designed as a challenging exercise for introductory science courses. We developed it specifically for non-science majors, but see no reason why it could not be used in majors courses as well. In either situation, The Story of Dinosaur Evolution will take a single class period and should be preceded by one or two classes which deal with the basic concepts of evolution. Before attempting this case, it is essential that students understand that evolution leads one to think of life in terms of a tree. A tree of life for a specific group of organisms represents gradual change over time from a common ancestor, and includes both speciation and extinction events. The Story of Dinosaur Evolution emphasizes the nature and complexity of the tree of life as well as teaches the specific evolutionary stories and anatomies of dinosaurs. The content of this case is taken directly from a review article by Paul Sereno entitled The Evolution of Dinosaurs (Science 284: , 1999). Instructors (and students) will find the original article very useful. A news article by Parsell (2002; along with a description of dinosaur hip anatomy by Boulton ( provide short, preliminary readings for students. Objectives Students will: Distinguish between ornithischians, sauropodomorphs, and theropods on the basis of physical characteristics. Trace the ancestry of individual dinosaur species from the common ancestor. Interpret a complex evolutionary tree which includes extinctions, speciation events, and changes in the number of taxa over time. Write The Story of Dinosaur Evolution. CLASSROOM MANAGEMENT This case is taught using an interrupted approach as described in the table below. Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 1

2 Table 1. Suggested Case Study Breakdown (55 80 mins) Step Task Time 1 Read case objectives (see above). 1 2 Break up into groups of 3 4 students such that each group becomes one of the three dinosaur groups. 3 As a class, become familiar with the names of 3 groups of dinosaurs: ornithischians ( bird-hipped croppers ), sauropodomorphs ( long-necked titans ), and theropods ( bipedal predators ). 4 Receive Handout I, which is copy of Figure 3 from the research article by Sereno (1999). As a class, address the question Which dinosaur is yours? by visually identifying each as either an ornithischian, a sauropodomorph, or a theropod. 5 In groups, create a list of Distinguishing Characteristics for a group of dinosaurs based on the figure in Handout I (all student groups make a list for their specific dinosaur group). The figure legend uses highly technical language, so use the Anatomical Dictionary provided and also focus attention on the pictures. 6 As a class, briefly share work from step # Receive Handout II, which is a copy of Figure 1 from the article by Sereno (1999). The 5 6 instructor provides a brief explanation of how to interpret each part of the figure. 8 Using the figure in Handout II, create a list of Evolutionary Events that took place during the evolution of a group of dinosaurs (all student groups make a list for their specific dinosaur group). In other words, What has happened to your group of dinosaurs over time? As a class, briefly share work from step # Write a story about the evolution of your group of dinosaurs based on the following criteria: Pretend that you are a particular dinosaur describing your family history. Tell your evolution story from the common ancestor of all dinosaurs all the way to your extinction. Include dates ( million years ago ). Include the word ornithischian, sauropodomorph, or theropod. Include at least 3 characteristics of your dinosaur (from Figure 3 provided in Handout I). You may choose to tell the story of your entire group or an individual family (i.e., Ornithurae) within your group Read stories aloud for open critique and comment by the class As a class, address the question, What are the commonalities of all stories of evolution? Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 2

3 BLOCKS OF ANALYSIS The following explanations correspond with the steps in the table above. Step 3 Students are asked to repeat the dinosaur names (ornithischian, sauropodomorph, and theropod) to become familiar with them. Instructors then briefly describe the 3 classes in the context of their names. The meaning of the descriptors for sauropodomorphs and theropods is obvious enough ( long-necked titans and bipedal predators, respectively). Bird-hipped croppers (the ornithischians) might be a little more confusing. Cropper refers to eating vegetation using a horny bill. Bird-hipped refers to the configuration of the hip joint where the pubis bone points backward, an important characteristic of later ornithischians which resembles the anatomy of modern birds. By contrast, the sauropodomorphs and theropods were both lizard-hipped because their pubis bone points forward (also called reptile-hipped ; for diagrams of hip structures, see Despite the descriptor birdhipped, note that birds did NOT evolve from the ornithischians. The prevalent explanation is that birds evolved from the theropods, as shown in the figure in Handout II from the Sereno article. For instructors who are a little more daring, you could ask students from each group to repeat their descriptor every time they hear their dinosaur name (throughout the entire class period). For example, every time the theropod group hears theropod, they should say bipedal predator. This is a bit juvenile, perhaps, but many students will find it humorous and learn the dinosaurs immediately. Also, prepared name tags for each dinosaur group may help students become comfortable with the unfamiliar names. Step 4 As explained in the legend for Figure 3 from the Sereno article in Handout I, the dinosaurs from left to right are examples of (A) an ornithischian, (B) a theropod, and (C) a sauropodomorph. Step 5 Many students will be able to generate a list of distinguishing characteristics using only Figure 3 in Handout I and its original legend. Nevertheless, the Anatomical Dictionary (Poling, 1998), which is specific to dinosaurs, will be very helpful for all of the students. Providing one color copy of the dictionary per group is sufficient. This may be collected at the end of class. Step 6 The legend for Figure 3 in Handout I explains many characteristics of each dinosaur, but in very technical language. Some key characteristics include the following: Ornithischian Horny beak for eating vegetation Long, flexible neck Hip joint resembles modern birds (pubis points backward) Theropod Large hands capable of grasping Mouth, teeth, and bite for eating other dinosaurs Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 3

4 Hollow skeleton to reduce bone weight (possibly related to the evolution of birds) Sauropodomorph Very large, in general Broad, fleshy feet to support weight Small head (relative to body) with mouth and teeth for slicing vegetation Step 7 Most introductory students will find Figure 1 in Handout II to be complex. In the context of this case, this complexity is intentional and will present a challenge for students in their groups as they struggle to interpret the story of their group of dinosaurs. Instructors must provide enough guidance for students to feel comfortable with Figure 1 while still allowing students to work through the particular evolutionary events in their groups. A possible explanation might go as follows: Figure 1 has four different parts to it. We ll briefly look at each part to help you orient yourselves before you examine the figure more closely in your groups. First, focus your attention on the dinosaur silhouettes at the top of the figure. Sauropodomorph group, which silhouettes represent your group? [The three long-necked titans in the middle, which stem from the Sauropodomorpha branch.] Theropod group, which silhouettes represent your group? [The seven bipedal predators on the right.] Ornithischian group, which silhouettes represent your group? [The thirteen bird-hipped croppers on the left.] Now focus your attention on the tree itself. At the bottom is the common ancestor of all dinosaurs. As you move up the tree, you move through time. Sometimes a species branches into multiple species, and sometimes species go extinct. In any event, you can trace evolutionary history from the common ancestor of all dinosaurs to the dinosaurs at the top which were present before the great extinction. Now focus your attention on the time scale at the far left. It starts in the Triassic and ends in the Cretaceous, spanning about 170 million years. Finally, focus your attention on the bar graph which is just to the right of the timescale. The bar graph estimates the number of different types of known dinosaurs (or genera). As you can see, dinosaurs experienced their greatest diversity just before their extinction. We also have to keep in mind that the knowledge in Figure 1 comes from the fossil record, and fossilization varies with species, location, and timing. Are there any questions? Does everyone feel comfortable with Figure 1? Note that this explanation does not include the shading of the bars in the tree, which is explained in the original figure legend. This point can be brought up in later discussions or, if the students are handling the figure well otherwise, it could be mentioned here. Step 8 Students may need to be reminded that evolutionary events include extinctions, speciation events, and changes in the number of taxa over time. Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 4

5 Step 9 Groups quickly share a couple of things that have happened to their group of dinosaurs over time. This step ensures that groups are headed in the right general direction before they attempt to write their stories. Step 10 While the students work in groups to write their stories, the instructor moves around the room to check drafts of their stories and address questions. Step 11 The stories will showcase student creativity as well as demonstrate what students do and do not understand. In particular, the stories often reveal misunderstandings about evolutionary relationships within Figure 1. It is important to correct students and guide them towards accepted interpretations. One unedited, humorous student story is provided below as an example: Back in the good old Triassic days, 235 million years ago, the dinosaurian was the ruler of the land. After much practice, it evolved into a sauropodomorpha. This was the very beginning of the Sauropoda family/dynasty. There was the Godfather, Sauropoda, and his two sons, Vulcanodon and Eusauropoda. Vulcanodon was attacked by an Eoraptor from the Theropod dynasty and killed because of insider trading and money laundering. Eusauropoda got with some broad and had Neosauropoda and the family continued with Titanosauriformes. And that was all in the Jurassic period. Then I was born, the Brachiosauride, in the Cretaceous period, 97 million years ago. I have a large body size (but I don t let it bother me) and a huge tail which is very intimidating as I must carry on my family s legacy. I take much pride in my arched ligament-bound metacarpus for digitigrade manual posture. After witnessing the deaths of some of my friends, I became a vegetarian. Step 12 Commonalities for all stories of evolution include the following: a common ancestor, gradual change over time, speciation events, and extinction events. Furthermore, evolution leads one to think of life in terms of a tree. Although The Story of Dinosaur Evolution is just one example of the tree of life, it demonstrates the common elements found on all major branches. REFERENCES Boulton, H. Dinosaur Evolution Classification of the Dinosaurs. Parsell, D.L. Scientist s Finds Spur New Thinking on Dino Evolution, National Geographic News, February 19, Poling, J. Anatomical Dictionary. October 19, Sereno, P.C The Evolution of Dinosaurs. Science 284: Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 5

6 FURTHER READING Boulton, H. Dinosaur Evolution. Acknowledgements: This case was developed with support from the National Science Foundation under Grant No as part of the Case Studies in Science Workshop held at North Carolina A&T State University on June 13 17, Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The authors thank Clyde Herreid, workshop participants, N.C. A&T students, Elon University students, and anonymous reviewers for their valuable feedback. Copyright 2005 by the National Center for Case Study Teaching in Science. Originally published 12/09/05 at Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work. Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 6

7 Handout I Fig. 3. Skeletal innovation in the three major clades of dinosaurs (Ornithischia, Theropoda, and Sauropodomorpha) as shown by contemporaneous species from the Upper Jurassic (Kimmeridgian) Morrison Formation of North America. Labeled features evolved at various nodes as described in the text. Scalebar, 1m. (A) Camptosaurus dispar, an ornithischian. (B) Allosaurus fragilis, a theropod. (C) Camarasaurus lentus, a sauropodomorph [after (44)]. Skeletal innovations are as follows: 1. horny beak for cropping; 2. predentary bone for lower bill support; 3. cheek depression for oral processing of plant matter; 4. leaf-shaped crowns with wear facets and a symmetrical enamel for shearing plant matter; 5. coronoid process for attachment of robust jaw-closing muscles; Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 7

8 6. opisthocoelous cervicals with reduced neural spines for flexibility; 7. ossified tendons to stiffen trunk; 8. rigid digit I with subconical ungual for defense; 9. pubis with prepubic process and posteroventrally directed postpubic process opening posterior trunk; 10. pendant fourth trochanter for enhanced caudal hindlimb retractors; 11. intramandibular joint for flexible bite; 12. metacarpal extensor depressions for manual raking; 13. hollow skeleton to reduce bone weight; 14. semilunate carpal simplifying wrist action to maneuver large hands; 15. manual digit II longest, emphasizing inner digits; 16. long penultimate phalanges enhancing grasping capability; 17. pubic foot for body support at rest; 18. astragalar ascending process uniting tibia and tarsus; 19. elongate prezygapophyses unite distal tail forming a dynamic stabilizer; 20. crowns with regular V-shaped wear facets indicate precise occlusion for slicing vegetation; 21. nares enlarged and retracted; 22. columnarlimbpostureforweightsupportatlargebodysize; or more opisthocoelous cervical vertebrae composing a longer neck; or fewer dorsal vertebrae shortening the trunk; 25. bifurcate neural spines accommodating a robust median elastic ligament; 26. arched ligament-bound metacarpus for digitigrade manual posture; 27. manual/pedal phalanges reduced in number for a more fleshy foot pad; 28. manual digits I and V weight-bearing to broaden support; 29. manual digit I ungual enlarged possibly for intraspecific rivalry; 30. distal tarsals unossiþed increasing shock-absorbing cartilage in joints; 31. elephantine pes for weight support at large body size. Credit: Reprinted with permission from The Evolution of Dinosaurs by Paul Sereno, Science 284, 25 june 1999, Copyright 1999 aaas. Readers may view, browse, and/or download the material on this page for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or in part, without prior written permission from the publisher ( Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 8

9 Handout II Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 9

10 Fig. 1. Temporally calibrated phylogeny of Dinosauria, showing known temporal durations (solid bars), missing ranges (shaded bars), and ranges extended by fragmentary or undescribed specimens (dashed bars). At left is tabulated the number of recorded nonavian dinosaurian genera per stage and an estimated curve of generic diversity, taking into account available out crop area (87). Basal or primitive taxa, in general, appear earlier in time than more derived members of a clade. Long missing ranges result from preservational bias against small body size (less than 2m), which truncates the early record of many clades, and from intervals for which there is little corresponding exposed terrestrial rock (such as the Middle Jurassic). The shaded zone (bottom) indicates the initial stage of the dinosaurian radiation before their dominance of land faunas in taxonomic diversity and abundance. Credit: Reprinted with permission from The Evolution of Dinosaurs by Paul Sereno, Science 284, 25 june 1999, Copyright 1999 aaas. Readers may view, browse, and/or download the material on this page for temporary copying purposes only, provided these uses are for noncommercial personal purposes. Except as provided by law, this material may not be further reproduced, distributed, transmitted, modified, adapted, performed, displayed, published, or sold in whole or in part, without prior written permission from the publisher ( Case Teaching Notes for The Story of Dinosaur Evolutions by Coker & Agnew Page 10