▁species . ▁The ▁vast ▁majority ▁of ▁pla cod erm s ▁were ▁pred ators , ▁many ▁of ▁which ▁lived ▁at ▁or ▁near ▁the ▁substr ate . ▁Many , ▁primarily ▁the ▁Ar th rod ira , ▁were ▁active , ▁ne k ton ic ▁pred ators ▁that ▁dw elled ▁in ▁the ▁middle ▁to ▁upper ▁port ions ▁of ▁the ▁water ▁column . ▁A ▁study ▁of ▁the ▁ar th rod ire ▁Comp ag op is cis ▁published ▁in ▁ 2 0 1 2 ▁concluded ▁that ▁pla cod erm s ▁( at ▁least ▁this ▁particular ▁genus ) ▁likely ▁possessed ▁true ▁teeth ▁contrary ▁to ▁some ▁early ▁studies . ▁The ▁teeth ▁had ▁well ▁defined ▁pul p ▁cav ities ▁and ▁were ▁made ▁of ▁both ▁b one ▁and ▁dent ine . ▁However , ▁the ▁to oth ▁and ▁j aw ▁development ▁were ▁not ▁as ▁closely ▁integrated ▁as ▁in ▁modern ▁g n ath ost om es . ▁These ▁teeth ▁were ▁likely ▁hom olog ous ▁to ▁the ▁teeth ▁of ▁other ▁g n ath ost om es . ▁ ▁One ▁of ▁the ▁largest ▁known ▁ar th rod ires , ▁D unk le ost eus ▁ter rel li ▁, ▁was ▁ ▁long , ▁and ▁is ▁pres umed ▁to ▁have ▁had ▁a ▁large ▁distribution , ▁as ▁its ▁remains ▁have ▁been ▁found ▁in ▁Europe , ▁North ▁America ▁and ▁possibly ▁Mor oc co . ▁Some ▁pale ont olog ists ▁regard ▁it ▁as ▁the ▁world ' s ▁first ▁verte br ate ▁" super pred ator ", ▁pre ying ▁upon ▁other ▁pred ators . ▁Other , ▁smaller ▁ar th rod ires , ▁such