Alternatively, the term "stem group" is sometimes used in a narrower sense to cover any members of the traditional taxon falling outside the crown group, such as the first cynodonts in the late Triassic being the first stem mammals. Permian synapsids like Dimetrodon or Anteosaurus are stem mammals in the wider sense but not in the narrower one.

Often, an (extinct) grouping is identified as belonging together. Later, it may be realized