▁likely ▁occurred ▁be ▁due ▁to ▁human ▁activity . ▁ ▁Ex cluding ▁Kal ou la ▁tap ro ban ica , ▁the ▁most ▁recent ▁common ▁ancest or ▁of ▁Kal ou la ▁likely ▁existed ▁about ▁ 2 2 . 3 ▁million ▁years ▁ago , ▁around ▁the ▁O lig oc ene – M i oc ene ▁boundary . ▁The ▁most ▁recent ▁common ▁ancest or ▁of ▁the ▁terrest rial ▁species ▁K . ▁rig ida ▁and ▁K . ▁w alter i ▁likely ▁lived ▁ 4 . 8 ▁million ▁years ▁ago ▁during ▁the ▁Early ▁P li oc ene , ▁while ▁that ▁of ▁the ▁ar b ore al ▁species ▁K . ▁k aling ensis ▁and ▁K . ▁k oka cii ▁likely ▁lived ▁ 9 . 1 ▁million ▁years ▁ago . ▁The ▁most ▁recent ▁common ▁ancest or ▁of ▁K . ▁conj unct a , ▁which ▁currently ▁has ▁four ▁recognized ▁sub species , ▁likely ▁lived ▁ 4 . 4 ▁million ▁years ▁ago . ▁ ▁Black burn , ▁et ▁al . ▁( 2 0 1 3 ) ▁suggests ▁that ▁Kal ou la ▁tap ro ban ica ▁might ▁not ▁form ▁a ▁cla de ▁with ▁the ▁other ▁Kal ou la ▁species , ▁although ▁it ▁does ▁clearly ▁form ▁a ▁cla de ▁with ▁Met aph ry n ella , ▁Ram an ella , ▁and ▁the ▁rest ▁of ▁Kal ou la . ▁ ▁Other ▁studies ▁rel ating ▁to ▁Kal ou la ▁ph y log eny ▁include ▁van ▁B oc x la er ▁et ▁al . ▁( 2 0 0 7 ), ▁M ats ui ▁et ▁al . ▁( 2