Definition of ammonoid in English:



  • An extinct cephalopod mollusk with a flat-coiled spiral shell, found commonly as a fossil in marine deposits from the Devonian to the Cretaceous periods.

    , → ammonite
    , and → goniatite
    • ‘The Triassic ammonoids represent the phylogenetic bridge between Paleozoic and Jurassic ammonoids.’
    • ‘In the Lower Devonian, ammonoids appeared, leaving us large limestone deposits from their shells.’
    • ‘Most of these are from swimming organisms, such as ammonoids and nautiloid mollusks that lived just above the deep seafloor.’
    • ‘In these periods, the ammonoids became extremely diverse, but comparatively little is known about their Early and Middle Viséan ancestry.’
    • ‘According to these studies, allometric growth is particularly common in Carboniferous and Permian ammonoids.’


  • Relating to the ammonoids.

    • ‘In summary, clymeniids fell well within the general range of Paleozoic ammonoid geometries, though most members of the Clymeniida tended toward an openly coiled shell with a low expansion rate.’
    • ‘The late Viséan was therefore the time in which the major Carboniferous ammonoid provinces were separated.’
    • ‘They are known to occur in abundance at only a few localities around the world and are entirely absent from some classic, highly diverse Permian ammonoid localities, such as the Urals in Russia and Kazakhstan.’
    • ‘This study, which represents part of my Ph.D. thesis, could not have been performed without the thorough taxonomic work carried out by many Triassic ammonoid systematists that has provided the basis for this study.’
    • ‘Curiously, other Cisuralian ammonoid localities in Nevada have yielded abundant ammonoids but no additional representatives of Uraloceras.’


Mid 19th century: from modern Latin Ammonoidea, based on Ammon (see ammonite).