How to Read a Cladogram
by Ara B.
A cladogram is defined as a tree diagram used to illustrate phylogenetic relationships. This means that it shows the evolutionary relationships between different animals. The cladogram can also show an animal’s path through time, and what traits it evolved during that path. A cladogram looks like a family tree but with lots of members. At the end of the cladogram is the end result: a specific animal, plant, or other organism. At the beginning of the cladogram is a single branch. This branch then splits several times into the several animals you have on a cladogram.
When you follow along a branch of the cladogram, it sometimes splits at nodes into two or more branches. In other words, two or more branches would sprout at that node. The node represents the branching point, and each node represents a new trait has been evolved and the common ancestor that evolved that trait. As you follow an animal’s path in the cladogram from the beginning to the end, you can find out the animal’s adaptations through time. Each node it goes through is a trait that it evolved, in that order.
You can also tell how closely related animals are on the cladogram. If you want to know the closest relative of one animal you trace its branch back to the most recent node. At this node you must follow the branch that does not lead to your animal but heads toward the end of the cladogram. The animal or animals that are at the end of this branch are the closest relatives to your animal. We know this because these animals are the only animals that share your animals most advanced trait and the common ancestor that evolved that trait.
Last updated April 6, 2007.