In common cladistic Cladistics is a form of biological systematics which classifies living organisms on the basis of shared ancestry. It can be distinguished from other taxonomic systems, such as phenetics, by its focus on evolutionary relationships; while other systems usually use morphological similarities to group similar species into genera, families and other usage, a monophyletic group is a taxon A taxon is a group of (one or more) organisms, which a taxonomist adjudges to be a unit. Usually a taxon is given a name and a rank, although neither is a requirement. Defining what belongs or does not belong to such a taxonomic group is done by a taxonomist. It is not uncommon for one taxonomist to disagree with another on what exactly belongs to (group of organisms) which forms a clade A clade is a term used in modern alpha taxonomy, the scientific classification of living and fossil organisms, to describe a monophyletic group, defined as a group consisting of a single common ancestor and all its descendants.[note 1], meaning that it consists of an ancestor and all its descendants. The term is synonymous with the uncommon term holophyly Holophyletic is a term posited as a semantically correct replacement for the term monophyletic as used by cladists . It originated amidst confusion over the correct definition for 'monophyletic group'; many definitions were available, of varying degrees of restrictiveness, and 'holophyletic' was posited as a term to describe the definition with. It is contrasted with the terms paraphyly In phylogenetics, a group of organisms is said to be paraphyletic if the group contains its most recent common ancestor but does not contain all the descendants of that ancestor, which is a taxon consisting of an ancestor and some of its descendants, and polyphyly For example, the group consisting of warm-blooded animals is polyphyletic, because it contains both mammals and birds, but the most recent common ancestor of mammals and birds was cold-blooded. Warm-bloodedness evolved separately in the ancestors of mammals and the ancestors of birds, so it is not a true phylogenetic grouping, which is a taxon that does not share a common ancestor.
However, this definition of the term took some time to be accepted. When the cladistic school of thought became mainstream in the 1960s, several alternative definitions were in use. Indeed, for some time taxonomists would use the term without even defining it, leading to great confusion in the early literature.[1]
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