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An Article by
Lesson developed by Larry Flammer
|This is an easily understood article which explains what cladistics is, why it is useful, how it is applied, and its limitations.|
1. Biological classification is intimately associated with evolution.
2. There are many problems encountered in classification, evidence that the living world is a work in progress; evolution provides an explanation for those problems.
3. Cladistics is one of several ways to show relationships, each addressing different problems in different ways.
The article in Natural History Magazine, June 1995, pp.33-35, including illustrations: "Why Cladistics?" by Eugene S. Gaffney, Lowell Dingus, and Miranda K. Smith. Check your school or local library for this issue.
If you can't find this issue, try this website:
1. Copies of article: "Why Cladistics?" for each student (see Materials)
2. Copies of Reading Guide for each student.
3. There is a shorter version of the Reading Guide, which might be suffiicient for your needs. This Reading Guide requires a password to access, which you can request from the webmaster using your school email address.
1. See "The De-riving Force of Cladogenesis" by Andrew J. Petto, on this site. It is a clear and concise explanation of the concepts and terms of cladistics. This could be copied and printed as a student handout. (Click on the "Back" button of your browser to return here.)
2. The UCMP (University of California Museum of Paleontology) has an excellent presentation of cladistics, phylogenies, and modern systematics (what, why, when, and how). Take a look at it: (<http://www.ucmp.berkeley.edu/exhibit/phylogeny.html>).
3. See the excellent online tutorial by the UCMP: "What did T. rex taste like?" It makes an excellent introduction to classification, phylogenetic trees, and cladistics. This could be given as a homework assignment (online).
4. For an excellent tutorial to introduce phylogenetic (evolutionary) trees, see our review of an article in the American Biology Teacher.
Some of the ideas in this lesson may have been adapted from earlier, unacknowledged sources without our knowledge. If the reader believes this to be the case, please let us know, and appropriate corrections will be made. Thanks.
1. Original Source: Larry Flammer, 7/95
2. Reviewed / Edited by: Martin Nickels, Craig Nelson, Jean Beard: 12/15/97
3. Edited / Revised for website by L. Flammer 3/24/98
The following is a useful worksheet for students to complete while reading the article, to help focus and direct their reading. A KEY follows, for teacher use, or for use by students as a self-check. These pages are also available in PDF format for easy downloading and printing using the FREE Adobe Reader (scroll to bottom of this screen).
An Article in Natural History Magazine, 6/95, by Gaffney, Dingus, and Smith
DIRECTIONS: Read the article, and answer all questions on separate sheet, in ink
1. Why is cladistics so popular right now?
2. What IS cladistics?
3. What kinds of problems does cladistics help us to solve?
4. In what way does cladistics differ from older methods?
5. What would a "hierarchy of nested groups" look like?
6. What is one of the shared derived characteristics by which the "dinosaur" group is included in the larger "vertebrate" group?
7. What is each group in an evolutionary tree called?__________; By what is it defined?
8. If cladistics is not a perfect method, why is it used?
9. If we relied on relative geological age, what relationship between dromaeosaurs and birds would be indicated?
10. What would cladistic analysis indicate regarding that relationship (#8)?
11. If cladistics does not specify ancestors and descendants, what does it do?
12. If geological age by itself is not a reliable basis for indicating relationships, what IS it used for?
13. Which features do we use to determine the evolutionary relationships between living animals?
14. Which features do we use to determine the evolutionary relationships between fossil animals?
15. What is wrong with using "armor" as an indicator of relationships in dinosaurs?
16. What is wrong with using "four limbs" as an indicator of relationships in dinosaurs?
17. How many shared derived characters are usually used, in real studies, to show evolutionary relationships?
18. What is done if patterns of character distribution conflict with each other?
19. What is the graphic depiction of the evolutionary relationships called?
20. Which cladogram version is considered the "best" (out of several which could be made for a particular group of organisms)?
21. Once the "best" cladogram is determined, what happens to it?
22. What are "primitive" features? Why?
23. What are "derived" or "advanced" features? Why?
24. The character "hole-in-hip-socket" is found only in what vertebrate groups?
25. Within what group is that feature (hole-in-hip-socket) a derived feature? Why"?
26. Within what group is that feature (hole-in-hip-socket) a primitive feature? Why"?
1. Best current scientific method for reconstructing evolutionary relationships.
2. (="phylogenetic systematics"); A method of determining evolutionary relationships of organisms.
3. Biological problems of evolutionary relationships, e.g. the origin of birds, and the geographic distribution of animals.
4. Uses distribution of features (shared derived characteristics) to test relationships.
5. Smaller groups contained within larger groups.
6. Backbone [spinal column].
7. Clade (not "phylogenies"); it is a set of shared derived characters inherited from a common ancestor.
8. It's more reliable and objective than geological age for determining relationships.
9. Earliest birds produced animals like Deinonychus and Velociraptor, etc.
10. A Deinonychus-like animal produced both birds and later to the dromaeosaurs, including Deinonychus and Velociraptor.
11. Tells us (hypothesizes) which animals are most closely related (most likely).
12. Provides context in which phylogenies can be placed.
13. Genetic, chemical, and behavioral characteristics.
14. Morphology [form] of the skeleton.
15. It's too limited (it's in only one group).
16. It's too widespread to be useful.
18. Specimens are re-examined carefully to see if they are well-enough preserved, and if the characters are really the same.
20. The one supported by the greatest number of characters.
21. It is subject to further scientific testing and possible revision (it's never final).
22. Those which define larger groups...thought to have evolved earlier.
23. Those shared by smaller groups...they evolved later.
24. The Dinosauria (all dinosaurs and birds).
25. All vertebrates (it's unique to the Dinosauria, so it's derived with respect to other vertebrates).
26. Sub-groups within the Dinosauria (since it's common to all Dinosauria, it must have evolved in the earliest Dinosauria).
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