▁he ▁considered ▁evidence ▁of ▁short , ▁un - joint ed ▁legs ▁in ▁Op ab in ia . ▁His ▁exam ination ▁of ▁the ▁anom al oc ar id ▁K ery g m ach ela ▁from ▁the ▁Si ri us ▁Pass et ▁l ager st ätte , ▁about ▁ ▁and ▁over ▁ 1 0 M   year s ▁older ▁than ▁the ▁Burg ess ▁Sh ale , ▁convinced ▁him ▁that ▁this ▁spec imen ▁had ▁similar ▁legs . ▁He ▁considered ▁the ▁legs ▁of ▁these ▁two ▁gener a ▁very ▁similar ▁to ▁those ▁of ▁the ▁Burg ess ▁Sh ale ▁A ys he a ia ▁and ▁the ▁modern ▁on ych op hor ans , ▁which ▁are ▁regarded ▁as ▁closely ▁related ▁to ▁the ▁ancest ors ▁of ▁ar th rop ods . ▁After ▁exam ining ▁several ▁sets ▁of ▁features ▁shared ▁by ▁these ▁and ▁similar ▁lo b op ods ▁he ▁drew ▁up ▁a ▁" bro ad - scale ▁reconst ruction ▁of ▁the ▁ar th rop od ▁stem - group ", ▁in ▁other ▁words ▁of ▁ar th rop ods ▁and ▁what ▁he ▁considered ▁to ▁be ▁their ▁evolution ary ▁" a un ts " ▁and ▁" c ous ins ". ▁One ▁striking ▁feature ▁of ▁this ▁family ▁tree ▁is ▁that ▁modern ▁tard igr ades ▁may ▁be ▁Op ab ini as ▁closest ▁living ▁evolution ary ▁relatives . ▁ ▁Although ▁Z hang ▁and ▁Brig gs ▁( 2 0 0 7 ) ▁disag re ed ▁with ▁Bud d ' s ▁diagn osis ▁that ▁Op ab ini as ▁" tri angles " ▁were ▁legs , ▁the ▁res embl ance ▁they