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International audienceDuring the Middle Oxfordian, numerous coral reefs flourished on the northern margin of the Tethys Ocean. The outcrop of Bonnevaux-le-Prieuré (northern French Jura mountains) provides a rare opportunity to observe a nearly complete section allowing the installation, evolution and demise of this global carbonate reef rich event to be studied. Quantitative data on coral assemblages together with sedimentological and palaeoecological observations lead to the reconstruction of a reef tract coral zonation. Starting from the outer slope, Dimorpharaea, Microsolena, Dendraraea, Comoseris, and Stylina ecozones are recognized. This new facies model implies a central position for an oolitic shoal in the highest energy zone, within the Comoseris ecozone. Applying this facies model to the sequence stratigraphic interpretation of the vertical succession results in recognising a third-order relative sea-level fluctuation, which can be correlated at least with Lorraine (France) and Switzerland

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The sections of Germig in the Nyalam area, southern Tibet, provide a continuous exposure of ammonoid-bearing, uppermost Triassic and basal Jurassic strata. Eighteen species (three of them new) are described and illustrated: Choristoceras marshi Hauer, C. aff. marshi, C. cf.

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The meaning of modifications in septal spacing that often coincide with maturity in extant Nautilus and fossil nautiloids, and also in ammonoids, remains controversial. In the Callovian nautilid species Paracenoceras marocense Miller and Collinson, 1952, the extent of decrease in septal spacing and the exceptional number of approximated septa are correlated with an unusual positive ontogenetic allometry in whorl-width expansion. This allometric growth implies that the threshold weight of the animal, requiring the formation of a new chamber to maintain near-neutral buoyancy, was reached for an increasingly shorter angular length of shell added to the aperture. Thus, the available space for the newly forming chamber behind the advancing body was reduced accordingly. Ontogenetic modifications in septal spacing are linked to relative growth of the animal. The flexibility in the mechanisms of buoyancy regulation would be expected to have been a critical factor affecting the possible set of ontogenetic trajectories in chambered cephalopods and thus the realm of variation upon which selection could act.