Lower Jurassic corals from Morocco with skeletal structures convergent with those of Paleozoic rugosan corals.

32 pagesInternational audienceNeorylstonia nom. nov. pseudocolumellata, a replacement name for Mesophyllumpseudocolumellatum Beauvais, 1986, is only known from uppermost Sinemurian touppermost Pliensbachian (Lower Jurassic) strata of Morocco. This solitary coral specieswent extinct during the Pliensbachian-Toarcian transition (~183.5 My), which iscurrently considered to be a second order biodiversity crisis linked to a period of rapidand global paleoenvironmental disturbances. Neorylstonia pseudocolumellata has adistinctive skeletal organization. The axial structure of the corallite, which has no equivalentin Mesozoic taxa, is reminiscent of the skeletal organization of some Paleozoicrugose corals such as Amygdalophyllum Dun and Benson, 1920, or Rylstonia Hudsonand Platt, 1927. This similarity is based on the occurrence of a calicular boss alsonamed pseudocolumella. As Rugosa and Scleractinia do not appear closely related,we consider that this feature cannot be due to evolutionary inheritance from a Rugosanancestor. The morphological aspects of the skeleton have been assessed in order tounderstand the function and growth of this axial “calicular boss” as well as to more preciselydescribe the genus and species characters. The organization of the septal apparatuspoints to a typical Scleractinian pattern, which is also supported by the originalaragonitic mineralogy of the skeleton. This implies a convergence phenomenon, leavingopen the question of the functional significance of such a calicular organization. Weposit that this feature was used for sexual reproduction and so did not always developin a population