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This message is posted for Maurizio Gnoli. Norm MacLeod ---------- Poise adaptations of shelled cephalopods represent, according to Pojeta & Mackenzie in Boardman, R.S., Cheetham, A.H. & A.J. Rowell (eds.) Fossil Invertebrates, 1987, p. 331, text-fig. 14.47, the major factor in early cephalopod radiation. Their shell's geometry represents one of the main factors to satisfy that purpose. Horizontal lifestyle in these molluscs could be reached by: a) extra shell weighting at the apical end of the chambered straight shell; b) Their chambered part may be reduced and may stil lie above the soft parts with the body chamber and aperture adapted to the poise (Phragmoceratida and Oncocerida); c) Liquid may be retained in the chambers to negate buoyant effects of the chambered shell; d) Their chambers may extend over the body tissues so that poise problems are reduced (Ascoceratids); e)The gas filled chambers may be shed so that they do not affect adult poise (? natural truncation); f) the chambered part may be coiled so that it lies above the body tussues (coiled nautiloids and Ammonoidea); Furthermore gas chambers may be lost (most Coleoidea). Above it's the exposed situation, now a simple question: which and how many of the listed above situations or devices could really existed, documented and proved? Leaving a part the possibility to fill and/or empty chambers such as it occurs now in living Nautilus when it generates a new septum (Ward, P.D., 1987). I shall be happy to receive any information on this topic, thanks in advance! Prof. Maurizio Gnoli **************************************** Maurizio Gnoli Dipartimento di Scienze della Terra (Paleontologia) Università degli Studi di Modena Via Universita', 4 41100 Modena ITALY e-mail: gnolim@unimo.it phone: +39-59-217084 fax: +39-49-218212 ***************************************
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