osa urus ▁is ▁a ▁genus ▁in ▁the ▁family ▁Di pl od oc idae . ▁It ▁is ▁one ▁of ▁the ▁more ▁bas al ▁gener a , ▁with ▁only ▁Am ph ico el ias ▁and ▁possibly ▁a ▁new , ▁un named ▁genus ▁more ▁primitive . ▁While ▁the ▁sub family ▁A pat osa ur inae ▁was ▁named ▁in ▁ 1 9 2 9 , ▁the ▁group ▁was ▁not ▁used ▁valid ly ▁until ▁an ▁extensive ▁ 2 0 1 5 ▁study . ▁Only ▁Br ont osa urus ▁is ▁also ▁in ▁the ▁sub family , ▁with ▁the ▁other ▁gener a ▁being ▁considered ▁syn onym s ▁or ▁rec lass ified ▁as ▁di pl od oc ines . ▁Br ont osa urus ▁has ▁long ▁been ▁considered ▁a ▁junior ▁syn onym ▁of ▁A pat osa urus ; ▁its ▁type ▁species ▁was ▁rec lass ified ▁as ▁A . ex c els us ▁in ▁ 1 9 0 3 . ▁A ▁ 2 0 1 5 ▁study ▁concluded ▁that ▁Br ont osa urus ▁is ▁a ▁valid ▁genus ▁of ▁sau rop od ▁distinct ▁from ▁A pat osa urus , ▁but ▁not ▁all ▁pale ont olog ists ▁agree ▁with ▁this ▁division . ▁As ▁it ▁existed ▁in ▁North ▁America ▁during ▁the ▁late ▁Jur ass ic , ▁A pat osa urus ▁would ▁have ▁lived ▁alongside ▁din osa urs ▁such ▁as ▁All osa urus , ▁Cam ar as aur us , ▁Di pl od ocus , ▁and ▁Ste g osa urus . ▁ ▁Description ▁ ▁A pat osa urus ▁was ▁a ▁large , ▁long - ne ck ed