Ontogeny of the skull of the Australian lungfish Neoceratodus forsteri (Osteichthyes: Dipnoi)

Abstract

Development of the sensory lines, dermal skull bones, neurocranium, quadrate, mandible and hyoid apparatus of the Holocene Australian lungfish Neoceratodus forsteri is described, beginning at stage 40, before the formation of any skeletal elements, until skull development is complete in the sub-adult fish. The sequence of the initial development of skeletal structures of the head and shoulder girdle reflects the need to feed and to acquire efficient gill respiration. The appearance of the neurocranium and dermal bones of the skull follows the formation of teeth, jaw bones and the cartilaginous quadrate, and the opercular bones, the skeletal elements directly associated with these functions. Dermal skull elements are closely related to the distribution of the sensory line system of the head. Each bone of the normal developing skull roof arises from a single centre of ossification, forming in a collagenous template secreted by mesenchymal cells. The numbers and arrangement of the skull bones found in the adult N. forsteri is the same as the pattern of bones laid down in the hatchling and juvenile, and the structures develop in an ordered and functional sequence.