ðə lˈeɪt kˈæmbɹiən fˈɑːsəl plˈɛktɹənˌoʊsɹəz ɪz nˈaʊ θˈɔːt təbi ðɪ ˈɜːlɪɪst klˈɪɹli sˈɛfɐləpˌɑːd fˈɑːsəl, æz ɪts ʃˈɛl hæd sˈɛptə ænd ɐ sˈaɪfʌŋkəl, ɐ stɹˈænd ʌv tˈɪʃuː ðæt nˈɔːɾɪləs jˈuːsᵻz tə ɹᵻmˈuːv wˈɔːɾɚ fɹʌm kəmpˈɑːɹtmənts ɪt hɐz vˈeɪkeɪɾᵻd æz ɪt ɡɹˈoʊz, ænd wˌɪtʃ ɪz ˈɔːlsoʊ vˈɪzᵻbəl ɪn fˈɑːsəl ˈæmənˌaɪt ʃˈɛlz.
The Late Cambrian fossil Plectronoceras is now thought to be the earliest clearly cephalopod fossil, as its shell had septa and a siphuncle, a strand of tissue that Nautilus uses to remove water from compartments it has vacated as it grows, and which is also visible in fossil ammonite shells.