Sutures and Septa in Jurassic Ammonite Systematics

Abstract

In the suborder Ammonitina the form of the septa and sutures is strongly influenced by whorl-shape and is often highly variable within the species and even the inidvidual. Claims that septa and sutures are specially significant because they are “internal characters” are refuted, as are also claims for overriding priority in classification for particular parts of the sutures, or for details of their early pntogenetic stages, or for the inner surfaces of the septa. Interpretation of the form of the septa and sutures as primarily conditioned by external water pressure is challenged. A recent revision of two superfamilies on the basis of septal form is held to involve unnatural groupings.