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A Mini-Lesson

Fossil Patterns:
Gradualism vs
Punctuated Equilibria

Original Lesson by William F. McComas and
Brian J. Alters

The original "Caminalcules" were created by Dr. Joseph H. Camin
and published by Dr. Larry Wiedman, 1991

Modifications by Larry Flammer




Two sets of simulated fossils (caminalcules) are provided as cutouts. Students arrange them on two time scales. One set produces a visual example of "gradualism", the other shows "punctuated equilibria".


1. Some evolutionary change is rapid and discontinuous, and some change is gradual.

2. Fossil patterns can provide clues to the past.

3. Speciation explains evolutionary branching and diversification.


Handout sheets

Envelopes with cut-out sets of two different groups of caminalcules.

Overhead of stratigraphic graph layouts

Overheads of results (2 keys): one for each genus


 (see end of lesson for the formatted handouts).

1. Introduction and Procedure sheet

2. Two stratigraphic sequence sheets for one genus (colored, attached end to end to form one large continuous time sequence), on which cutout caminalcules will be placed in sequence.

3. Envelope with one set of cutout caminalcules (one genus, matching the sequence sheets)

4. Sheet with Discussion questions on one side, and two small stratigraphic graph layouts on the other.


1. This lesson can be presented near the end of a unit which introduces the essential nature of evolution, or it could be used later in the course, in a more detailed treatment of the elements of speciation. In either case, it does reflect the real existence of two patterns of fossil sequences found in nature, and does provide one of several reasonable explanations for the smaller percentage of transitional (intermediate) fossils than one might expect in the fossil record.

2. Run off copies of the two sets of caminalcules (put one set on one color, e.g. pink, and the other set on a different color, e.g. yellow). Make enough sets so that there is enough of one set for half your class (one set per pair of students), and enough of the other set for the other half of your class. If you have 32 students, run off 8 sets of pink Pedivarious sets, and 8 sets of yellow Molluscaformis sets. You will only need one classroom set for re-use in all classes, and every year, but run off some extras, just in case! If the labels on your downloaded copies are not clear, email me (webmaster) and I'll send you hard copy).

3. Have your students cut the caminalcules apart, cutting as close to each animal as can be done easily (keeping age of each attached). This should be done on some day prior to doing this lesson; use any equitable time frame to do this, so that everyone in every period has a little share of the "action". For example, one class can work on 4 sheets of one genus, with every student cutting out two creatures. This would take only about 5-10 minutes total time out every class for 4 periods (to do all 16 sheets). Be sure all the creatures of each set gets into its own pre-labeled envelope. (You can have someone label 8 envelopes: "Molluscaformis", and someone else label 8 envelopes: "Pedivarious").

4. Make copies of the Stratigraphic Sequence sheets. You will need enough of one set (double sheets) for half your class, and likewise for the other set. Do this in colors which will contrast with the cut-out caminalcules. For example, run the two Molluscaformis sheets on green paper, and the Pedivarious sheets on blue. If possible, tape the two sheets of one color together, so the bottom end of the top sheet (with title) just overlaps the top end of the bottom sheet. It helps to cut off one margin or the other, so the time charts are contiguous. Keep these charts flat (not folded), so they will lay flat on the table tops when in use.

5. Make enough copies for everyone (or every team of two) of the Discussion questions on one side, and the two small Stratigraphic Sequence graphs (side by side) on the other side.

6. At the beginning of the period, hand out the lesson title sheet, with the introduction and directions, to be read by students during the taking of roll.

7. Assign your students to work in pairs, and give each pair one set of Stratigraphic Sequence sheets, and one envelope of matching caminalcules. Assign so that any two adjacent teams have different genera.

8. Before allowing your students to proceed, you might want to show an overhead version of one of the Stratigraphic Sequence charts, (not the key version), and quickly show (with marker, or small cutout pieces) how they might begin placing the fossils. For many classes, this won't be necessary; the printed directions are sufficient.

9. As students work on the layouts, circulate, offering help where needed. Make one circuit to hand out the wrap-up sheets (Discussion questions on one side, two "blank" sequence graphs on the other, for making a line diagram of the pattern they develop.

10. When all or most teams seem to be getting the patterns expected, you might want to take a few minutes to have them look at an adjacent team's pattern. Do they see the difference? You might even show them on the overhead the "key" diagrams for each genus. Do this quickly, then remove them, and let each team (or individual) make its line drawing of the patterns seen, and answer the discussion questions. Alternatively, you could walk the class through the discussion together.


1. A similar activity is offered in the "Macroevolution" lesson. Although less elaborate, it may be worth considering as an alternative. It has the strong advantage of using "real" shells (paper cutouts of real shells), as found in successive layers).

2. A different approach, with a somewhat different focus, but still looking at large paleontological patterns, is presented in a recent issue of the American Biology Teacher (April, 1999) by Anton Lawson (see reference below). The focus is more on critical thinking, forming testable hypotheses to challenge three "theories" about the origin of the diversity of life: spontaneous generation, special creation, and evolution. Many of the hypotheses can be tested simply by studying a sampling of fossils representative of the geological column, figuratively "gathered on a field trip into the Grand Canyon". Types and inexpensive sources of fossils you could use for this activity are presented in a companion article in the same issue of the ABT by James Platt (see reference). A sample handout for students, along with tips and strategies for the teacher are clearly presented. Looks like a winner. If you try this activity, please give us your feedback.

3. Use this simple "evolutionary tree" diagram to show:
.......a. how microevolution over time can result in macroevolution, ...
.......b. how classification relates to evolution, and...
.......c. the meaning of evolution.

4. SPECIAL NOTE: Click here to explore many of the different lines of evidence pointing to speciation and macroevolution.

5. MACROEVOLUTION DIAGRAM: See the Macroevolution Diagram and a page of directions for using that diagram on an overhead projector. This nicely shows how accumulated speciations can eventually form all the groups and subgroups of organisms. It also shows how classification is related to evolution. A very nice colorful version of this can be found on page 32 of that most useful resource: Teaching About Evolution and the Nature of Science, by the National Academy of Sciences (1998) (see our Resources section). A particularly interesting alternative diagram is the one Darwin included in The Origin of Species (chapter IV), the only diagram in that book! His discussion there of that diagram should be required reading for any biology teacher. Darwin's Tree makes a great overhead transparency for discussing his concept of evolution by natural selection, as well as how classification reflects that evolution.


Lawson, Anton E. "A Scientific Approach to Teaching About Evolution & Special Creation". The American Biology Teacher, vol.61, no.4, April 1999, pages 266-274).

Platt, James E. "Putting Together Fossil Collections for 'Hands-On' Evolution Laboratories". The American Biology Teacher, vol.61, no.4, April 1999, pages 275-281).

Gendron, Robert F. 2000. "The Classification & Evolution of Caminalcules." The American Biology Teacher, October 2000, pp. 570-576. Includes sharp diagrams of "living" and "fossil" caminalcules and a Caminalcule Evolutionary Tree that those caminalcule "specimens," when properly arranged, would likely display. Excellent vehicle for questions probing and analyzing fossils and phylogeny.
---> This article is available free to NABT members on the website archive. For issues archived since January 2000, CLICK HERE, click on Members Only (left column), enter email address and password, on Welcome page, click on American Biology Teacher, then find desired issue.


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 for this leson: William F. McComas & Brian J. Alters ("Modeling Modes of Evolution: Comparing Phyletic Gradualism & Punctuated Equilibrium". The American Biology Teacher, vol.56, no.6, September 1994, pages 354-356. Also in Investigating Evolutionary Biology in the Laboratory, edited by William F. McComas, 1994, NABT, pages 131-141.

2. The original "Caminalcules" are imaginary creatures created by Dr. Joseph H. Camin (1922-1979), of the Dept. of Entomology at the Univ. of Kansas. They were first published by Dr. Larry Wiedman in 1991 in his Lab Manual for College Level Oceanography (ISBN 0-314-00473-4) and West Publishing. Dr. Wiedman is currently at the Univ. of Saint Francis, 2701 Spring St., Fr. Wayne, IN 47808 (e-mail lwiedman@sf.edu).

3. This lesson (Peek at the Past) Edited / Revised for website by L. Flammer 4/99


 The following are useful worksheets for students. The first one provides an introduction and directions. The second one ask questions to be completed during the activity (one per team, or one per student, if you prefer). These are also offered in pdf format. The other sheets are offered in PDF format only (see further down), since they are diagrams.

A PEEK AT THE PAST: Fossil Patterns, Gradualism, or Punctuated Equilibria?

Every now and then, paleontologists uncover what appears to be a complete series of fossils. They find batches of fossils which seem to represent a population of one species, living at one period of time, and showing a typical range of variation, but still clearly members of one species. As they search layers of sediment above and below, they find more fossil groups of what appear to be the same species.

As paleontologists study the entire series of fossils, they tend to find two kinds of patterns. Sometimes there appear to be slight shifts in the average features of the fossils over time, eventually becoming so different from the earliest form that they have to say a new species has formed. But with another series of fossils (may be a totally different kind of organism), they find very little difference for long periods of time, then, all of a sudden,they begin to find fossils similar to the earlier ones, but showing some striking differences, clearly a new species. Sometimes, in both cases, the original species continues to exist along with the new species, and sometimes the original species can no longer be found.

The purpose of this exercise is to reconstruct these patterns, compare and contrast them with each other, and arrive at some conclusions about what happens to the species over time. (The "fossils" in this study are imaginary, for easier analysis, but they do accurately represent what we find in the fossil record). One group of fossils represents the genus Molluscaformis (elongated, sausage shaped), the other represents the genus Pedivarious (short thick body, with thick black markings on it).

You will be provided with a collection of fossils representing one of these genera. You will also be provided with a two-page layout which shows the layers of sedimentary rock from which the fossils were taken (the "Stratigraphic Sequence"). Each layer ("Formation") is identified with a unique name, and an indication of how long it took to form (its "duration").

1. Place the two "Stratigraphic" sheets so that the title sheet is above the other, and the identical parts of their ends overlap perfectly.

2. Place the fossils in the Fossil Sequence" column) according to the "Formation" from which they were taken. "Upper" means it was found in the upper (more recent) portion of that formation; "Lower" means it was found in the lower (older) portion of that formation. (The little numbers in parentheses indicate the number of fossils which are represented by that one "average" fossil shown).

3. Once all the fossils are arranged chronologically (from the oldest at the bottom, to the youngest near the top), start adjusting their horizontal positions (representing their overall morphology, or appearance of form). This usually works best if you place the lowest (oldest) fossil in the lower left corner of the work space column. If the next fossil above it is identical in appearance, place it directly above the first. If it appears slightly different, place it above and slightly to the right of the one below it. If there is a major difference in form (appearance), shift it even more to the right. Repeat this with each fossil as you move up the column.

4. If there appears to be two kinds of fossils at the same level, check the fossils further up, and look for a consistent pattern of change away from (different from) the lower sequence; locate those fossils further to the right. If the differences are very slight, show this with very slight shifts to the right. If they have major differences, shift them even more to the right.

5. Once you have your pattern developed, ask your teacher to check it. If it represents the arrangement described above, then diagram the pattern on the appropriate chart, using simple lines to represent the sequence of fossils through time. The result may look like a leaning branching tree, or it may look like a couple of vertical or near vertical lines.

6. Assign a proper species name to the original species, and to any other species which may have formed. You can invent the trivial part of the name, reflecting some unique feature of that species, e.g. "M. megawings". Print their names next to each somewhat vertical line on your chart. Use the form "M. species" or "P. species" in each case.

7. Answer the discussion questions for that particular genus.


Name___________________________________SN____ Date_____________ Per.___


Molluscaformis Fossils (color:_______________)

1. How would you describe these fossils generally through time (except for any "sudden" major change)?

[ ] static (generally unchanging), or [ ] non static (gradually changing)?


2. Have any new species evolved? _______. If so, how many?_____. In which formation did it/they first appear?


3. Have any species apparently become extinct?______ If so, which one(s)?

(For each extinction, indicate in which formation its last fossils were found?)



4. Which pattern of evolution seems to be occurring here?

[ ]"Gradualism", in which changes to new species are gradual, followed by continuous little changes, or

[ ]"Punctuated Equilibrium", in which changes to new species appear to be sudden, followed by little or no change

5. Would you be likely to find any intermediate or transitional fossils if we searched more thoroughly in the formation just below the first appearance of changed fossils?______ Why?



Pedivarious Fossils (color:______________)

1. How would you describe these fossils generally through time (except for any "sudden" major change)?

[ ] static (generally unchanging), or [ ] non static (gradually changing)?


2. Have any new species evolved? _______. If so, how many?_____. In which formation did it/they first appear?


3. Have any species apparently become extinct?______ If so, which one(s)?



(For each extinction, indicate in which formation its last fossils were found?)

4. Which pattern of evolution seems to be occurring here?

[ ]"Gradualism", in which changes to new species are gradual, followed by continuous little changes, or

[ ]"Punctuated Equilibrium", in which changes to new species appear to be sudden, followed by little or no change

5. Would you be likely to find any intermediate or transitional fossils if we searched more thoroughly in the formation just below the first appearance of changed fossils?______ Why?


Some of these files are large and may be slow-loading

 Two sheets: Intro, Directions, and Discussion Questions

One sheet: Stratigraphic graphs for two genera

One sheet: Key to Molluscaformis graph

One sheet: Key to Pedivarious graph

One sheet: Two sets of caminalcules
Print on different colored paper for each set.

High resolution (300 dpi),
slower loading pages of caminalcules (1 MB each).
Very sharp, but reduce each 50% for copies
for students to use on Tabletop Time Scales.
Be sure name labels are still readable.
Print on different colored paper for each set:
Sheet 1: Pedivarious
Sheet 2: Molluscaformis

High Resolution (300 dpi) KEYS:
Suitable for overhead projector, on which you can
trace the main phylogenetic pathways for each phylogeny,
using an overhead marker
Key: Pedivarious Phylogeny
Key: Molluscaformis Phylogeny

Two sheets: Tabletop Time Scale for Molluscaformis

Two sheets: Tabletop Time Scale for Pedivarious


 The following pages are in Adobe Acrobat pdf format in order to maintain their intended layout for easy printing of handouts. Only a "thumbnail" reduced size image of the first page is showing (if more than one page is in that file). For enlarging and copying, (and seeing other pages in that file), you will need to download the free Acrobat Reader from Adobe (unless it's already installed in your system). Then just click on the blue file name above, below, or next to the first page. You may see the "Acrobat Exchange" (Reader application) loading, then the pages will display. You might need to shift-click and drag the lower left corner of the page to enlarge it, or click the magnifying glass on the menu bar.

If this doesn't seem to work, you might need to load and/or enable the PDFViewer plug-in by following one of these protocols:

For Netscape Communicator: EDIT>Preferences>Navigator>Applications (then scroll down to "Portable Document Format (PDFViewer)", click on it, then click OK; if it's not there, click on "New", and add it in).

For Netscape Navigator: OPTIONS>General Preferences>Helpers (scroll to check for PDF on list, add it if it isn't, then click OK to activate it.

For other browsers, or problems with this, check with your browser tech support, Adobe tech support, or, in dire frustration, e-mail me. If nothing else, I will mail you hard copy of the formatted pages desired.

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