Cladistics is a study of the classification of biological organisms based on shared characteristics and common ancestors. A cladogram is a visual chart or representation of cladistics. They consist of horizontal or vertical lines connecting various organisms. These different lines branch off from a common point on the cladogram. These branch points represent a common ancestor shared by the organisms that emanate from the branch point. Please note that this ancestor is a hypothetical ancestor and not necessarily an actual organism. It is used to view what a common ancestor might look like based on common traits from the organisms it connects.