olf ▁( Can is ▁dir us ), ▁and ▁the ▁American ▁l ion ▁( Pan ther a ▁le o ▁at ro x ), ▁among ▁many ▁others . ▁ ▁The ▁noted ▁American ▁foss il ▁collect or ▁and ▁pale ont ologist ▁E . ▁D . ▁C ope ▁was ▁a ▁student ▁of ▁Le id y ' s , ▁but ▁the ▁en m ity ▁and ▁r uth less ▁competition ▁that ▁developed ▁between ▁him ▁and ▁rival ▁pale ont ologist ▁O . ▁C . ▁Marsh ▁eventually ▁drove ▁Le id y ▁out ▁of ▁western ▁American ▁verte br ate ▁pale ont ology , ▁a ▁field ▁that ▁Le id y ▁had ▁helped ▁to ▁found . ▁Marsh ▁claimed ▁Le id y ▁contributed ▁to ▁the ▁falling ▁out ▁of ▁the ▁two ▁by ▁showing ▁C ope ▁in ▁the ▁presence ▁of ▁Marsh ▁that ▁C ope ▁had ▁mistaken ly ▁placed ▁the ▁head ▁of ▁a ▁foss il ▁El asm osa urus ▁on ▁the ▁tail , ▁rather ▁than ▁on ▁the ▁neck , ▁and ▁then ▁publishing ▁a ▁correction . ▁ ▁Le id y ▁was ▁an ▁early ▁American ▁supp orter ▁of ▁Dar win ' s ▁theory ▁of ▁evolution , ▁and ▁lo bb ied ▁successfully ▁for ▁Dar win ' s ▁election ▁to ▁membership ▁in ▁the ▁Academy ▁of ▁Natural ▁Sciences ▁of ▁Philadelphia . ▁ ▁In ▁ 1 8 5 2 ▁Le id y ▁referred ▁B ison ▁anti qu us , ▁the ▁North ▁American ▁foss il ▁b ison , ▁to ▁the ▁genus ▁B ison , ▁the ▁first ▁to ▁do ▁so . ▁Sometimes ▁called ▁the ▁" anci ent ▁b ison ", ▁it ▁was ▁the ▁most ▁common ▁large