▁to ▁contain ▁only ▁a ▁single ▁species , ▁C im ol opter y x ▁r ara . ▁The ▁only ▁known ▁spec imen ▁confident ly ▁attributed ▁to ▁C . ▁r ara ▁was ▁found ▁in ▁the ▁L ance ▁Form ation ▁of ▁Wy oming , ▁d ating ▁to ▁the ▁end ▁of ▁the ▁Ma astr icht ian ▁age , ▁about ▁ ▁million ▁years ▁ago . ▁A ▁second ▁dub ious ▁species , ▁" C im ol opter y x " ▁maxim a , ▁has ▁been ▁described ▁from ▁both ▁the ▁L ance ▁Form ation , ▁and ▁the ▁Hell ▁Creek ▁Form ation ▁of ▁Mont ana . ▁ ▁Description ▁and ▁history ▁C im ol opter y x ▁was ▁a ▁fairly ▁small ▁bird , ▁with ▁a ▁maximum ▁size ▁about ▁equal ▁to ▁that ▁of ▁a ▁small ▁g ull . ▁It ▁is ▁known ▁almost ▁exclus ively ▁from ▁a ▁number ▁of ▁cor ac oid s ▁( a ▁b one ▁in ▁the ▁shoulder ▁g ird le ). ▁These ▁have ▁a ▁distinct ▁enough ▁an atom y , ▁however , ▁to ▁allow ▁it ▁to ▁be ▁distinguished ▁from ▁other ▁birds , ▁and ▁even ▁for ▁distinct ▁species ▁to ▁be ▁recognized . ▁The ▁first ▁such ▁cor ac oid ▁to ▁be ▁found ▁( spec imen ▁number ▁Y MP ▁ 1 8 4 5 , ▁in ▁the ▁collections ▁of ▁the ▁Pe ab ody ▁Museum ▁of ▁Natural ▁History ) ▁was ▁first ▁mentioned ▁and ▁inform ally ▁named ▁by ▁pale ont ologist ▁O th n iel ▁Charles ▁Marsh ▁in ▁the ▁foot note ▁of ▁an ▁ 1 8 8 9 ▁paper , ▁but ▁it ▁was ▁not ▁valid ly