▁top ▁occur ▁only ▁in ▁the ▁mid - section , ▁and ▁there ▁is ▁no ▁sign ▁that ▁the ▁t ough ▁" shell " ▁plate ▁on ▁the ▁animal ' s ▁back ▁was ▁segment ed ; ▁hence ▁in ▁their ▁opinion ▁Od ont og ri ph us ▁could ▁not ▁have ▁been ▁an ▁ann el id . ▁On ▁the ▁other ▁hand , ▁wr ink les ▁are ▁seen ▁in ▁the ▁feet ▁of ▁dead ▁ch it ons . ▁W iw ax ia , ▁they ▁argued , ▁was ▁clearly ▁not ▁segment ed , ▁as ▁the ▁numbers ▁of ▁s cler ites ▁in ▁its ▁three ▁concent ric ▁groups ▁did ▁not ▁match ▁at ▁all . ▁They ▁critic ized ▁But ter field ' s ▁main ▁argument ▁for ▁" sh oe hor ning " ▁W iw ax ia ▁into ▁the ▁pol ych a etes , ▁that ▁its ▁s cler ites ▁were ▁secret ed ▁by ▁micro villa e ; ▁such ▁structures , ▁they ▁wrote , ▁were ▁also ▁found ▁in ▁several ▁groups ▁of ▁m oll us cs . ▁Finally , ▁in ▁their ▁opinion ▁the ▁absence ▁of ▁" leg s " ▁in ▁W iw ax ia ▁ruled ▁out ▁a ▁close ▁relationship ▁with ▁pol ych a etes . ▁ ▁In ▁ 2 0 0 8 ▁But ter field ▁described ▁a ▁set ▁of ▁micro - f oss ils ▁dated ▁to ▁between ▁ ▁and ▁, ▁found ▁in ▁the ▁Ma ht o ▁Form ation ▁in ▁Al berta ' s ▁Jas per ▁National ▁Park ▁– ▁this ▁foss il ▁bed ▁is ▁ 5 ▁– ▁ 1 0 ▁M ▁years ▁older ▁than ▁the ▁Burg ess ▁Sh ale