Caminalcules and Phylogenies
Objectives
Understand the purpose of a phylogeny.
Learn what characteristics are useful in building a phylogeny
Construct a phylogeny for a fictitious set of organisms: caminalcules
Caminalcules & Constructing a Phylogeny
A phylogeny is a ‘family’ tree linking species together based on their historical relationships.
This is similar to a family tree that links parents to children. One difference is that one species
can give rise to two daughter species rather than two parents giving rise to an offspring.
Therefore the tree begins with the single most ancestral stock and typically branches as new
species evolve.
To give you the opportunity to construct a phylogeny (without requiring you to dedicate the next
decade of your life to the task), you are provided with hypothetical creatures, both living and
fossilized, called Caminalcules. These creatures can be arranged in a phylogenetic tree based on
the characteristics of each Caminalcule. In other words, your task today will be to arrange the 14
‘living’ species into a phylogenetic tree of Caminalcules. The goal here is to build a phylogenetic
tree based on homologous characters. The trick of course, is to decide what are homologous
characters and what are analogous characters.
So what constitutes a shared homologous character? This is a characteristic shared between two
or more species because the characteristic was present in a common ancestor and then passed on
to the descendant species. An analogous character, however, can lead to false trees. If two or
more species shared a characteristic that was not derived from a common ancestor, the species
may be linked together much more closely on the tree than they would have if that character was
ignored.
For your assignment today, you are to construct a phylogeny for the living caminalcules (the ones
with no number in parentheses). In your group, discuss what characteristics you think seem most
ancestral and which seem to have evolved much later in time. Use characteristics that allow you
to decide which caminalcule species is the most ancestral (that is has changed little from the
original ancestor) and build a phylogenetic tree that includes all 14 living species. It is important
to keep track of what characters you used to decide how to build the tree.
CAMINALCULES
Modified from Robert P. Gendron
Indiana University of Pennsylvania
Caminalcules are imaginary animals invented by the evolutionary biologist Joseph Camin. They
make ideal organisms for introducing students to phylogeny. These organisms illustrate how
modern classification schemes attempt to reflect evolutionary history. In the process of doing this
exercise, students are also introduced to concepts such as convergent evolution and vestigial
structures. The pictures of the Caminalcules are copyrighted by the journal Systematic Biology
and Robert R. Sokal. They are made available here with permission.
The Classification and Evolution of Artificial Organisms
Bi102 Caminalcules I 1
