Primitive (phylogenetics)
In phylogenetics, a primitive (or ancestral or basal) character, trait, or feature of a lineage or taxon is one that is inherited from the common ancestor of a clade (or clade group) and has undergone little change since. Conversely, a trait that only appears in some members of the clade group, but not all, is called advanced or derived.
Source: Wikipedia — Primitive (phylogenetics) (CC BY-SA 4.0)