Gregarious growth versus colonial habit in the rugose coral family Geyerophyllidae Minato, 1955

Abstract

The family Geyerophyllidae Minato, 1955 includes corals having clinotabulae, lonsdaleoid dissepiments and a variable complex axial structure formed as an extension of the cardinal septum. Included in the family are four genera originally considered to have a colonial (fasciculate) growth habit - Carniaphyllum Heritsch, Carinthiaphyllum Heritsch, Lonsdaleoides Heritsch, and Darwasophyllum Pyzhyanov. More recent studies and a review of the type specimens of Carniaphyllum, Carinthiaphyllum and Lonsdaleoides have shown them to be solitary corals with a gregarious growth habit. In its original description and in all subsequent works, Darwasophyllum has consistently been referred to as a fasciculate coral, but the presence of offsets has not been illustrated in the genus and a colonial growth habit has not been clearly demonstrated. Early Serpukhovian specimens of Darwasophyllum from the Etherington Formation (Mississippian) in Canada were initially regarded as fasciculate colonies with long, sub-parallel, closely spaced corallites. When they were studied in detail by means of serial sections, however, these corals were found to be solitary individuals grouped into gregaria, without shared structures or offsets. Thus, true colonies are unknown in the Geyerophyllidae and all genera described as colonial in that family consist of gregarious, solitary corals.