Osteogenesis in the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi)

ABSTRACT Several types of bone development are present in the Australian lungfish, Neoceratodus forsteri, the only extant member of the family Neoceratodontidae. In this species, dermal and parachondral bones form around the chondrocranium and mandible, to protect the brain and sense organs, to support the dentition and to facilitate oral function. The notochord persists throughout life. The quadrate and Meckel’s cartilage remain cartilaginous, as does the chondrocranium. Anterior elements of the hyoid arch, the basihyal and hypohyals, do not ossify. The ceratohyal, which articulates with the hypohyals, ossifies perichondrally, as do the exoccipital bone and the ribs of the trunk, including the cranial rib. The exoccipital bone is embedded in the chondrocranium in the adult fish, and the cranial rib is immobile. Some elements of the skeleton, such as the pectoral and pelvic fins, and the pelvic girdle, remain cartilaginous, and the skeletal elements in these fins resemble the structure of the tail. Fully developed bone is trabecular or lamellar, and does not include vascular elements. Endochondral ossification does not occur in the living Australian lungfish.