Potyphyllum, a new phillipsastreid genus of rugose corals in the Upper Frasnian of Belgium with precisions about the age of the Petit-Mont Member

1. IntroductionThis work serves as conclusion for the revision of massive rugose corals belonging to the family Phillipsastreidae Roemer, 1883 and occurring in the Upper Frasnian of Belgium. The diverse species of Frechastraea Scrutton, 1968 have been investigated in detail by Coen-Aubert (2012, 2015). As for Phillipsastrea D’Orbigny, 1849, P. falsa Coen-Aubert, 1987 and P. ranciae Coen-Aubert, 1987 were described by Coen-Aubert (1987) and P. conili Tsien, 1978 was studied by Coen-Aubert (1994). The present paper is concerned with two pseudocerioid species like Frechastraea, but with larger corallites, which have been previously ascribed to Phillipsastrea, but which are herein assigned to the new genus Potyphyllum based on Cyathophyllum ananas Goldfuss, 1826 as type species. Most Belgian occurrences of Potyphyllum ananas and P. veserense (Coen-Aubert, 1974) characterize the Upper Palmatolepis rhenana conodont Zone. As mentioned by Coen-Aubert (2012, 2015), the base of the Upper Frasnian has been fixed by the Subcommission on Devonian Stratigraphy, at the entry of the conodont Palmatolepis semichatovae. In Belgium, the entry of P. semichatovae is observed within the Lower Palmatolepis rhenana Zone, together with the first occurrence of Ancyrognathus triangularis whereas the massive rugose coral Frechastraea coeni Coen-Aubert, 2012 can be considered as an excellent marker for the base of the Upper Frasnian. As it is explained by Coen-Aubert (2015), the expression Namur Basin is