Geology 105 - Paleontology
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Reading: Ch. 5, Web & Gould

For this assignment, we will use four reading resources:

Chapter 5, p. 129-135.

Gould, S. J., 1983, What, If Anything, is a Zebra?, Hen's Teeth and Horse's Toes: Further Reflections in Natural History, New York: W.W. Norton & Co., pp.355-365.

Evolution 101: Patterns - click through all the web pages in this section of Evolution 101

Biological Diversity: Classification



taxon - a grouping of organisms
taxonomy - sorting organisms into groups
systematics - the study of the diversity of organisms, including evolutionary patterns
shared derived characters -
clade -
homologous -
analogous -


Key Concepts and Questions:

1. Basics of biological classification (Biological Diversity: Classification)

A. Hierarchical groups:

Kingdom, Phylum, Class, Order, Family, Genus, Species

natural groups:

Kingdom; fundamentally different kinds of creatures (e.g., plant, animal, fungus, etc.)

Phylum - different body architectures (e.g., Arthropods have jointed appendages, segmented body, chitinous exoskeleton)

Family - recognizable kind of organism; e.g., squirrel, cat, human

Species - specific kind of organism; red squirrel, Asiatic lion, modern human


B. Naming: Suppose you find a fossil brachiopod? What do you have to do to name the species?




2. Why Classify? Read the Gould Article for these questions.

A. To identify morphologic groups - organisms that look like the "same kind" of creature.

E.g., it's easier to refer to "fish" than to "vertebrate organisms with gills and fins that live in the water"

B. To represent evolutionary relationships.

Are all fish more closely related to each other than to other groups?





C. To create a database for answering biological questions, e.g., biodiversity


3. Changing approaches

Traditional biological classification is hierarchical, resulting in a system that looks like this.

This approach puts organisms with similar characteristics in similar boxes, and lumps some boxes together into higher level boxes, but does not tell us how related the boxes at the same level are to each other.

So paleontologists produced diagrams of evolution through time that looked like trees, like this one of horses.

But the linkage between the two kinds of diagrams is messy. Where are the hierarchical boxes on the horse evolutionary tree?

And our classification system does not automatically tell us about how the organisms are related to each other.

In the past few decades, biologists have come up with another approach: cladistic analysis, well described in Evolution 101: Patterns (be sure to click through all the pages in the Patterns section)

A. Briefly describe the sequence of steps in doing cladistic analysis (let's call the diagrams that are produced phylogenetic trees or cladograms).






B. How is a cladogram different from the evolutionary tree of the horses?




C. How would classification derived from cladistic analysis be different than the traditional Linnean groups (family, order, etc.)?





Short Answer: Compare the three schools of biological classification (traditional taxonomy, cladistics, phenetics) based on goals, methods, use of characters, and areas of objectivity/subjectivity.


Debate over cladistic classification has been particularly bitter among paleontologists working on ancient reptiles, dinosaurs and birds. Here is a statement from the Web page of an evolutionary biologist:

Of [the three] basic approaches to taxonomy, I prefer the evolutionary (traditional) approach. The reasons for this are summarized as follows:

  1. The information content is higher.
  2. It promotes greater stability.
  3. It enhances ease of use.
  4. It results in a more balanced classification.

Discuss this statement first from the viewpoint of an traditional taxonomist, then from a cladistic viewpoint. Use the example of the classification of reptiles, birds and mammals to argue each side. Be sure you address each of the points listed above for each of the classification systems.