Candy Cladistics
Introduction:
Cladistics groups organisms together by the features, or characteristics, that they
share. Organisms that evolved from the same ancestors have the same shared characteristics,
the same way that you and your siblings probably share the same hair and eye color because
you are descended from the same parents. The relationships of organisms are shown in a
branching diagram called a cladogram.
Assumptions made by cladistics:
Organisms of a clade are related by descent from a common ancestor.
Change in characteristics occurs in lineages over time.
The simple cladogram below is an example of how things are grouped together using
cladistics.
tall spiral
spiral shell
shell with one opening shared characteristics
In a cladogram, the places where the branches meet are called nodes (circles have
been drawn at the nodes in the cladogram above). Every organism at the end of a branch that
comes from the same node is part of the same group, called a clade. The shared
characteristics written next to a node defines the clade that comes off of that node. The same
cladogram is shown below and the clades that come off of each node have been circled. The
name written next to each node is the name of the clade branching from that node.
Clades are usually given names so that they’re easier to refer to. In the snail cladogram,
it’s much easier to name the “Gastropods” than to keep calling it “the clade with the animals that
have spiral shells.” When you define a clade using shared characteristics, you also give it a
name, so that the next time you use the name “Gastropods,” other people know that you’re
talking about “the animals that have spiral shells.” Lots of the groups that you’re familiar with
Gastropods
Conchifers
Marine Gastropods
Moon snail
