Cladograms represent hypotheses about evolutionary relationships—who is more closely related to whom.

These relationships are based on shared features that have been inherited from a common ancestor.

A short red bar on the cladogram shows that feature 1 evolved before the common ancestor of A and C.

The long red bar at the top of the cladogram shows that organisms A, B, and C inherited feature 1.

Over time, evolution occurs and some features change.

The changes are also inherited.

Feature 2 evolved before the common ancestor of B and C, and is inherited by B and C.

A does not have this feature.

Feature 3 evolved in the lineage leading to organism C.

So, feature 1 provides evidence that A, B, and C are more closely related to each other than to other organisms, and feature 2 tells us that B and C are more closely related to each other than to A.

Feature 3 is unique to C.

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Now, let's see how we can use this information to study the vertebrates.