Total group

Total group



When referring to a systematic grouping, there is a danger of confusion between the crown and total groups, although they mean different things. For example, simply referring to a fossil as a "bird" does not tell you whether it is a familiar example derived from the last common ancestor of all living forms, or whether it is a more basal form. (By definition, all living forms fall into the crown group.)

Since all total groups correspond to a crown group, some systematists have suggested using a standardized prefix (e.g., "Pan-") to form names of total clades from the names of their corresponding crown clades. For example, "Panmammalia" (or "Pan-Mammalia" or pan-Mammalia) would be the total clade including "Mammalia" but no living non-mammals. Others have pointed out that there are already names for many total clades; for example, "Synapsida" and "Theropsida" have both been used to refer to the total mammalian clade.

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