Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
The lungfishes, one of the three subclasses of Osteichthyes. In comparison with Devonian lungfishes, extant species have reduced the number of median fins, changed the shape of the tail, and decreased ossification of the braincase and other endochondral bones.
The recent family Lepidosirenidae includes five species from Africa and South America. Lepidosirenids have eellike bodies, filamentous paired fins, two lungs, tooth plates with three cutting blades, a greatly reduced skull roof, and an elongated ceratohyal important in suction feeding and respiration. Lepidosirenids are obligate air breathers, and the heart, arterial tree, and gills are highly specialized. To breathe air, the fish protrudes its snout from the water surface, gulps air into the mouth, and then forces it into the lung by closing the mouth and raising the floor of the oral cavity.
The family Ceratodontidae is represented by the single species Neoceratodus forsteri from Australia. They are stout-bodied with large scales, leaf-shaped paired fins, and tooth plates with flattened crushing surfaces. Adults reach more than 3 ft (1 m) in length. The diet includes plants, crustaceans, and soft-bodied invertebrates.
Early dipnoans were marine; fresh-water adaptations occur in Paleozoic and most post-Paleozoic dipnoans. Burrowing habits developed independently in late Paleozoic gnathorhizids and extant lepidosirenids. Dipnoans were common worldwide from the Early Devonian to the end of the Triassic, but are rare since. They are restricted to the southern continents in the Cenozoic.