Sunday, January 29, 2012


When I was a graduate student at the University of Illinois, I was a teaching assistant for a class called History of Life - a class I liked so much I developed it for the community college where I teach now.  It's an overview of the origin and evolution of life on Earth.  Why is this taught by a geologist rather than a biologist?  Because much of what we know about the origin and evolution of life is preserved in the sedimentary rock record and paleontology, the study of ancient life, is typically housed in geology departments (although there's obviously much overlap with fields like molecular biology).

At the University of Illinois, the course had a lab while at our community college it doesn't (although we do incorporate lab-like exercises into class time including the examination and classification of common marine invertebrate fossils). One of the lab exercises at the U of I had to do with the classification of caminalcules.

What are caminalcules, you may ask?   They are imaginary "life forms" invented by the late Joseph Camin, an evolutionary biologist at the University of Kansas, and used to illustrate concepts in systematics (evolutionary relationships and classification).

After Camin's death, biologist Robert Sokal, a cofounder of the field of numerical taxonomy, published four detailed papers on caminalcules for the journal Systematic Zoology (now called Systematic Biology).  See the references below but fair warning, I have these papers - don't bother getting them unless you're an academic, they will be unreadable.

The concept involved is actually easy to understand (even for children as we'll see in a minute).  What Camin did was invent 29 recent "species" and 48 fossil "species" of caminalcules (most people use a dataset today of 14 living and 57 fossil specimens).  The earliest fossil caminalcule was seen as the ancestor of all subsequent forms which evolved through a multi-branched evolutionary tree (with some lineages becoming extinct, etc.).  At left is an animated gif illustrating one sequence of 13 evolving caminalcules (from Caminalcules, Snouters and Other Unusual Creatures).

There is an official "correct" version of the caminalcule phylogenetic tree showing the evolutionary relationships between the fossil and recent species.  I would suggest ignoring it, however, since the purpose of the exercise isn't necessarily to get a correct answer but to think about the process (students absolutely hate it when I tell them for some exercises there's no "correct" answer, just a well-reasoned and supported answer).

So what exactly do you do with caminalcules?  First you get the images of living and fossil caminalcules (here and here are good sources) and then cut them all out.  Then you get some paper - preferably a roll of brown paper you can pick up at any office supply store - and roll out a couple of feet.

Note that the caminalcules are all numbered, this is so individual specimens can be referred to, but the fossil specimens also have a number in parentheses.  This is the age of the fossil in millions of years ago.  So specimen 74, for example, has the number 18 in parentheses so we can assume specimen 74 represents a fossil that was living some 18 million years ago.

On your long sheet of paper, draw 20 evenly spaced horizontal lines and label them 0-19.  These represent time lines from 0 (present day) to 19 Ma (oldest fossil caminalcule).  Then arrange your fossil caminalcules on the various time lines according to their ages.

By the way, geologists use the abbreviation Ma to denote millions of years ago (mega annum).

Now comes the fun part.  Figure out the evolutionary relationships between the various species.  The assumption, of course, in this hypothetical exercise, is that all caminalcules can trace their descent back to the original 19 Ma form.  Caminalcules evolve (and perhaps lose) various anatomical traits as they evolve.  Some become more specialized (or maybe more generalized).  Some lineages become extinct.  Some split into many branches.  Some don't.  Some persist through time as "living fossils".  It's up to you to figure it out.  When you believe you have a good phylogenetic tree, tape or glue down the caminalcules and draw lines indicating the relationships.

As I've mentioned before in this blog, my wife and I homeschool our two children.  They recently did this exercise (along with a couple of other homeschooled kids) and below is my ten-year-old son's finished product (can't see the faint pencil lines, but they're drawn in as well).

It's pretty cool that the same exercise can be used in homeschooled 5th graders as well as freshman college students (it can even be used for graduate students in conjunction with Sokal's papers listed below).  My wife reported that my 10-year-old son told her, after he did this exercise, that "This is like all life on Earth, only all of life would be more complicated."  Warms my heart to hear that.


Gendron, Robert P. 2000. The Classification and Evolution of Caminalcules. The American Biology Teacher 62 (8): 570–576.

On the Cutting Edge: Professional Development for Geoscience Faculty. Caminalcule Phylogenetic Exercise.   Teaching Paleontology in the 21st Century.

Sokal, R.R. 1983. A phylogenetic analysis of the Caminalcules. I. The data base. Systematic Zoology 32 (2): 159–184.

Sokal, R.R. 1983. A phylogenetic analysis of the Caminalcules. II. Estimating the true cladogram. Systematic Zoology 32 (2): 185–201.

Sokal, R.R. 1983. A phylogenetic analysis of the Caminalcules. III. Fossils and Classification. Systematic Zoology 32 (3): 248–258.

Sokal, R.R. 1983). A phylogenetic analysis of the Caminalcules. IV. Congruence and Character Stability. Systematic Zoology 32 (3): 259–275.

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