▁lower ▁j aws , ▁is ▁more ▁likely ▁evidence ▁of ▁the ▁b ite ▁of ▁a ▁medium - s ized ▁mos as aur ▁pre ying ▁upon ▁am mon ites . ▁ ▁Some ▁am mon ites ▁appear ▁to ▁have ▁lived ▁in ▁cold ▁see ps ▁and ▁even ▁reprodu ced ▁there . ▁ ▁Sh ell ▁an atom y ▁and ▁divers ity ▁ ▁Basic ▁shell ▁an atom y ▁▁ ▁The ▁chamber ed ▁part ▁of ▁the ▁am mon ite ▁shell ▁is ▁called ▁a ▁ph rag mo con e . ▁It ▁contains ▁a ▁series ▁of ▁progress ively ▁larger ▁ch amb ers , ▁called ▁camera e ▁( sing . ▁camera ) ▁that ▁are ▁divided ▁by ▁thin ▁walls ▁called ▁sept a ▁( sing . ▁sept um ). ▁Only ▁the ▁last ▁and ▁largest ▁chamber , ▁the ▁body ▁chamber , ▁was ▁occupied ▁by ▁the ▁living ▁animal ▁at ▁any ▁given ▁moment . ▁As ▁it ▁grew , ▁it ▁added ▁newer ▁and ▁larger ▁ch amb ers ▁to ▁the ▁open ▁end ▁of ▁the ▁co il . ▁Where ▁the ▁outer ▁wh or l ▁of ▁an ▁am mon ite ▁shell ▁largely ▁covers ▁the ▁preceding ▁wh or ls , ▁the ▁spec imen ▁is ▁said ▁to ▁be ▁invol ute ▁( e . g ., ▁An ah op l ites ). ▁Where ▁it ▁does ▁not ▁cover ▁those ▁preceding , ▁the ▁spec imen ▁is ▁said ▁to ▁be ▁evol ute ▁( e . g ., ▁D act y li oc eras ). ▁ ▁A ▁thin ▁living ▁t ube ▁called ▁a ▁si ph un cle ▁passed ▁through ▁the ▁sept a , ▁extending ▁from ▁the ▁am mon ite