AMMONOID SHELL STRUCTURES OF PRIMARY ORGANIC COMPOSITION

摘要: Palaeozoic and Mesozoic cephalopod conchs occasionally reveal dark organic coatings at the aperture. A number of these coatings, including still unrecorded examples, are described, figured interpreted herein. On basis elemental analysis, actualistic comparison a with Triassic bivalves, some shown to consist apatite primarily probably conchiolin (and also melanin). In several ammonoid genera such as Paranannites, Psiloceras, Lytoceras, Phylloceras, Harpoceras Chondroceras, (recorded herein for most taxa first time) structure similar black band, which was previously known only from Recent Allonautilus Nautilus. contrast nautilid genera, however, material ammonoids not deposited on inside shell but externally, albeit positioned terminal aperture in nautilids. Some Carboniferous age show bands more or less regular angular distances ultimate whorls aperture, e.g. Nomismoceras, Gatherites, Owenites, Juvenites Melagathiceratidae gen. et sp. nov. Oman shows that coating secreted inside, because position this deposit changes interior exterior an anterior direction (i.e. adaperturally). This has been referred ‘false colour pattern' is here having formed interim megastria (‘alter Mundrand'). All structures discussed paper considered have by single organ initiated form stress adverse conditions. Thus, certain environmental parameters growth anomalies appear influenced their formation.