Groups that do include all the descendants of the most recent common ancestor are said to be monophyletic. A paraphyletic group is a monophyletic group from which one or more of the clades is excluded to form a separate group (as in the paradigmatic example of reptiles and birds, shown in the picture). A group that does not contain the most recent common ancestor of its members is said to be polyphyletic (Greek πολύς (polys), "many").