Unusual offsetting in Serpukhovian (Lower Carboniferous) representatives of the rugose coral genus Schoenophyllum Simpson, 1900

Schoenophyllum has been described as a columellate, fasciculate genus in which the corallites bear slender lateral processes regarded as supporting structures or as tubules connecting adjacent corallites. Recent investigation of Serpukhovian specimens from the Etherington Formation and its lateral equivalents in western Canada has shown these lateral processes to be sub-horizontal to moderately elevated tubule-like structures forming the initial stages of new offsets and commonly containing tabulae. They locally reach and may interfere with the walls of neighbouring corallites, but remain structurally distinct from them and do not allow communication between parent and adjacent corallites. The initial, tubule-like stage is followed by a steeply elevated to vertical, sparsely septate stage in which the axial structure is developed as a prolongation of the cardinal septum. The origin and nature of the axial structure suggests assignment of Schoenophyllum to the family Petalaxidae.