7 ) ▁div ides ▁the ▁Am m ono idea , ▁regarded ▁simply ▁as ▁an ▁order , ▁into ▁eight ▁sub orders , ▁the ▁An arc est ina , ▁C ly men i ina , ▁G oni at it ina , ▁and ▁Pro le can it ina ▁from ▁the ▁Pale oz o ic ; ▁the ▁Cer at it ina ▁from ▁the ▁Tri ass ic ; ▁and ▁the ▁Am mon it ina , ▁Ly to cer at ina , ▁and ▁Ph yl loc er at ina ▁from ▁the ▁Jur ass ic ▁and ▁C ret ace ous . ▁In ▁subsequent ▁tax onom ies , ▁these ▁are ▁sometimes ▁regarded ▁as ▁orders ▁within ▁the ▁subclass ▁Am m ono idea . ▁ ▁Life ▁ ▁Because ▁am mon ites ▁and ▁their ▁close ▁relatives ▁are ▁ext inct , ▁little ▁is ▁known ▁about ▁their ▁way ▁of ▁life . ▁Their ▁soft ▁body ▁parts ▁are ▁very ▁rarely ▁preserved ▁in ▁any ▁detail . ▁Non eth eless , ▁much ▁has ▁been ▁worked ▁out ▁by ▁exam ining ▁am m ono id ▁shell s ▁and ▁by ▁using ▁models ▁of ▁these ▁shell s ▁in ▁water ▁t anks . ▁ ▁Many ▁am m ono ids ▁probably ▁lived ▁in ▁the ▁open ▁water ▁of ▁ancient ▁se as , ▁rather ▁than ▁at ▁the ▁sea ▁bottom , ▁because ▁their ▁foss ils ▁are ▁often ▁found ▁in ▁rocks ▁laid ▁down ▁under ▁conditions ▁where ▁no ▁bottom - d well ing ▁life ▁is ▁found . ▁Many ▁of ▁them ▁ ▁( such ▁as ▁Ox yn otic eras ) ▁are ▁thought ▁to ▁have ▁been ▁good ▁sw imm ers , ▁with ▁fl