Primitive (or
ancestral) in
phylogenetics means a character, trait or feature of a lineage or
taxon that is inherited from the common ancestor of a
clade (or clade group) and has undergone little change since. Conversely, a trait that appears
within the clade group (that is, is present in any subgroup within the clade but not all) is called
advanced or
derived. A
clade is a group in which all members have the same common ancestor.