Scientist use synapomophies, or shared derived characters, to define cladograms. For instance, mammary glands are a shared characteristic of mammals. All mammals and their oldest common ancestor, had or have mammary glands.Thus, if we are looking at an unidentified animal and trying to place it in a cladogram, if it has mammary glands we know it belongs in that branch. Cladogram is a diagram used to represent a hypothetical relationship between groups of animals, called a phylogeny. A cladogram is used by a scientist studying phylogenetic systematics to visualize the groups of organisms being compared, how they are related, and their most common ancestors.
