us ▁as ▁a ▁bas al ▁l oph ot ro cho zo an , ▁in ▁other ▁words ▁close ▁to ▁the ▁last ▁common ▁ancest or ▁of ▁m oll us cs , ▁ann el id ▁w orm s ▁and ▁bra chi op ods . ▁ ▁History ▁of ▁discovery ▁ ▁Charles ▁D ool ittle ▁Wal c ott ▁found ▁one ▁spec imen ▁during ▁one ▁of ▁his ▁field ▁tri ps ▁to ▁the ▁Burg ess ▁Sh ale ▁between ▁ 1 9 1 0 ▁and ▁ 1 9 1 7 . ▁In ▁the ▁ 1 9 7 0 s ▁Simon ▁Con way ▁Morris ▁re - ex am ined ▁the ▁spec imen ▁and ▁tent atively ▁concluded ▁that ▁it ▁was ▁a ▁sw imming ▁l oph op hor ate , ▁in ▁other ▁words ▁related ▁to ▁the ▁ancest ors ▁of ▁m oll us cs , ▁ann el id ▁w orm s ▁and ▁bra chi op ods . ▁In ▁ 2 0 0 6 ▁Car on , ▁Sch el tem a ▁et ▁al . ▁published ▁a ▁new ▁analysis ▁based ▁on ▁ 1 8 9 ▁recently ▁collected ▁spec im ens , ▁all ▁from ▁the ▁Burg ess ▁Sh ale . ▁ ▁Description ▁ ▁Od ont og ri ph us ▁was ▁apparently ▁a ▁very ▁rare ▁species , ▁account ing ▁for ▁less ▁than ▁ 0 . 5 % ▁of ▁the ▁individual ▁organ isms ▁found ▁in ▁the ▁same ▁foss il ▁b eds . ▁Most ▁of ▁the ▁foss ils ▁consist ▁of ▁two ▁parts ▁of ▁a ▁split ▁block ▁of ▁rock , ▁the ▁upper ▁part ▁giving ▁a ▁" cast ing " ▁of ▁the ▁animal