urus ▁individual ▁originally ▁described ▁as ▁Atl ant osa urus ▁im man is ; ▁as ▁a ▁consequence , ▁some ▁elements ▁cannot ▁be ▁as cribed ▁to ▁either ▁spec imen ▁with ▁confidence . ▁Marsh ▁distinguished ▁the ▁new ▁genus ▁A pat osa urus ▁from ▁Atl ant osa urus ▁on ▁the ▁basis ▁of ▁the ▁number ▁of ▁sac ral ▁verte bra e , ▁with ▁A pat osa urus ▁possess ing ▁three ▁and ▁Atl ant osa urus ▁four . ▁Two ▁years ▁later , ▁Marsh ▁announced ▁the ▁discovery ▁of ▁a ▁larger ▁and ▁more ▁complete ▁spec imen ▁at ▁Como ▁Bl uff , ▁Wy oming . ▁He ▁gave ▁this ▁spec imen ▁a ▁new ▁name ▁based ▁on ▁the ▁convent ions ▁of ▁his ▁age ▁and ▁the ▁relatively ▁sparse ▁foss il ▁record ▁available ▁at ▁that ▁time . ▁It ▁was ▁later ▁recogn ised ▁that ▁the ▁features ▁he ▁had ▁used ▁to ▁distinguish ▁gener a ▁and ▁species ▁were ▁in ▁fact ▁more ▁w ides p read ▁among ▁sau rop ods . ▁He ▁named ▁the ▁new ▁species ▁Br ont osa urus ▁exc els us . ▁All ▁spec im ens ▁currently ▁considered ▁A pat osa urus ▁were ▁from ▁the ▁Mor r ison ▁Form ation , ▁the ▁location ▁of ▁the ▁exc av ations ▁of ▁Marsh ▁and ▁C ope . ▁ ▁Another ▁spec imen , ▁in ▁the ▁American ▁Museum ▁of ▁Natural ▁History ▁under ▁spec imen ▁number 4 6 0 , ▁which ▁is ▁occasionally ▁assigned ▁to ▁A pat osa urus , ▁is ▁considered ▁nearly ▁complete ; ▁only ▁the ▁head , ▁feet , ▁and ▁sections ▁of ▁the ▁tail ▁are ▁missing , ▁and ▁it ▁was ▁the ▁first