 These authors also provide a phylogenetic tree of the mammalian members of the family, showing that they fall into five recognizable subfamilies, four of which exhibit deep branching sub-subfamilies.However, all sequences within a subfamily are >60% identical while those between subfamilies are >40% identical.As also shown by Hagenbuch and Meier, all but one (OatP4a1) of the mammalian homologues cluster together, separately from all other animal (insect and worm) homologues.