Biology 4344 (Evolution and Systematics)
Spring 2020
Dr. Starkey
Part I: Introduction to Classification
All life on Earth is descended from simple life forms that arose approximately 4
billion years ago. When all living organisms are examined, they can be placed
into what is commonly referred to as the Tree of Life (TOL). In this tree, there are
organisms that “branched” out early whereas others branched out much more
recently. This suggests that some branches on the TOL represent organisms that
are “closely” related (recent Common Ancestry) whereas as other are “distantly”
related and may no longer show any indication that the organisms were once
related (no recent common ancestor). The overall history being illustrated by the
TOL can be difficult to “see” because, in most instances, we are only looking at
extant (living) organisms. In other words, we are trying to figure out what the tree
looks like but only looking at the tips of the branches. As a result, the true
structure of the tree is hidden and can only be revealed if we examine organisms
that have become extinct i.e., fossils.
Fossils, or fossil data, are incredibly important to the TOL but as we have
discussed fossilization is rare and finding fossils is even rarer. If we are fortunate
enough to find fossils what issues do we need to consider? We have discussed
some of these issues previously, but we will revisit them now. The first thing we
want to consider is whether, or not, the characteristics we are examining in the
