▁considered ▁par ap hy let ic , ▁a ▁series ▁of ▁subsequent ▁off sh o ots ▁from ▁the ▁main ▁stem - line ▁of ▁ igu and ont ian ▁evolution . ▁It ▁is ▁instead ▁placed ▁in ▁the ▁cla de ▁Had ros aur iformes , ▁closely ▁related ▁to ▁the ▁Had ros au ro idea , ▁which ▁contains ▁the ▁Had ros aur idae ▁( also ▁known ▁as ▁" du ck - bil led ▁din osa urs ") ▁and ▁their ▁closest ▁relatives . ▁Our an osa urus ▁appears ▁to ▁represent ▁an ▁early ▁special ized ▁branch ▁in ▁this ▁group , ▁showing ▁in ▁some ▁tra its ▁independent ▁convergence ▁with ▁the ▁had ros aur ids . ▁It ▁is ▁thus ▁a ▁bas al ▁had ros aur iform . ▁ ▁The ▁simplified ▁cl ad ogram ▁below ▁follows ▁an ▁analysis ▁by ▁Andrew ▁Mc Donald ▁and ▁colle agues , ▁published ▁in ▁November ▁ 2 0 1 0 ▁with ▁information ▁from ▁Mc Donald , ▁ 2 0 1 1 . ▁ ▁Pale obi ology ▁ ▁Diet ▁The ▁j aws ▁were ▁apparently ▁operated ▁by ▁relatively ▁weak ▁mus cles . ▁Our an osa urus ▁had ▁only ▁small ▁temporal ▁open ings ▁behind ▁the ▁eyes , ▁from ▁which ▁the ▁larger ▁cap iti - m and ib ular is ▁mus cle ▁was ▁attached ▁to ▁the ▁cor ono id ▁process ▁on ▁the ▁lower ▁j aw ▁b one . ▁Small ▁rounded ▁horn s ▁in ▁front ▁of ▁its ▁eyes ▁made ▁Our an osa urus ▁the ▁only ▁known ▁horn ed ▁orn ith op od . ▁The ▁back ▁of ▁the ▁sk ull ▁was ▁rather ▁narrow ▁and