Autapomorphy vs. Synapomorphy — What's the Difference?

In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to the focal taxon (which may be a species, family or in general any clade).

An evolved character or trait that is shared by two or more taxonomic groups and is considered to have originated in their common ancestor. Hair is synapomorphic for marsupials, primates, and all other taxa that are grouped together in the class Mammalia.

An autapomorphic character.

(cladistics) A derived trait that is shared by two or more taxa of shared ancestry.

An evolved character or trait that is unique to a single species or group within a larger phylogenetic group. Speech is an autapomorphy of humans among primates.

(cladistics) A derived trait that is unique to a particular taxon