| mhorn | Дата: Sunday, 30.09.2012, 20:52 | Сообщение # 1 |
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| Dommergues J.-L., Goolaerts S. (2012) Oxyarietites boletzkyi n. gen., n. sp., nouveau genre et nouvelle espèce d’ammonite dans le Sinémurien inférieur de Bourgogne (France): un rare précurseur des morphologies oxycônes pour le Jurassique // Geodiversitas 34 (3): 517-529. http://dx.doi.org/10.5252/g2012n3a4
http://www.mnhn.fr/museum/front/medias/publication/46435_g2012n3a4.pdf
One of the very first quasi-oxycone ammonites following the Triassic/Jurassic boundary crisis is described. It was collected from the fossiliferous Lower Sinemurian (Semicostatum or Turneri Chronozone) strata of Burgundy (Mavilly-Mandelot, Côte-d’Or, France). The new taxon, Oxyarietites boletzkyi n. gen., n. sp., possesses an involute, compressed and keeled shell of suboxycone morphology, a shell type previously unknown for the Lower Sinemurian. The discovery makes younger by about 2 Ma the emergence of keeled (sub)oxycone shells following the Triassic/Jurassic boundary crisis. Its obviously keeled ventral area allows a probable assignation to the Arietitoidea Hyatt, 1875 sensu Guex (1995) superfamily, but family level assignation and its evolutionary origin remain obscure. Although, it is generally accepted that involute, compressed and keeled suboxycone and oxycone ammonite shells possess the best hydrodynamical abilities and mobility, the acquisition of this probable adaptive advantage in O. boletzkyi n. gen., n. sp. does not go together with abundancy in the fossil record
Middle Jurassic - Lower Cretaceous ammonites & aptychi
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