Lungfish fossils first appear at the beginning of the Devonian period, about 400 million years ago. Once distributed around the world, lungfish now occur in only three areas (South America, Africa, and Australia) that were once adjacent but have since separated due to continental drift. South American and African lungfish are more closely related to one another. They have reduced gills and two lungs and are true air breathers, while Australian lungfish have one lung and rely mostly upon their gills for respiration, gulping air at the water surface to breathe only when dissolved oxygen is in short supply.
African and South American Lungfish
There are two related families in this order. The African family, Protopteridae, has one genus (Protopterus) and four species (P. annectens, P. aethiopicus, P. dolloi, and P. amphibius). They live in the rivers, lakes, and swamps of East and Central Africa and grow to 2 meters (6.5 feet) in length. The South American family, Lepidosirenidae, has only one species, Lepidosiren paradoxa. It lives in swampy areas of the Amazon and ParanГЎ river basins and in the swamps of the Chaco region and grows to 1.2 meters (4 feet) in length. During spawning season, males dig holes for the eggs and guard both eggs and young after they hatch. The South American male develops branched, gill-like structures on his pelvic fins that may supply extra oxygen to himself as he incubates and to his offspring. Juveniles hatch with adhering organs to attach to plants. They have external gills like salamander young and undergo metamorphosis. Adults live on crustaceans, mollusks, and small fishes. They survive the dry season by resting quietly in moist burrows dug in the mud. If it becomes too arid, they seal their burrows with mud, secrete a protective covering of mucus, and estivate, sometimes for several months. During estivation, metabolism slows down to conserve energy and air. Once the rainy season begins, water enters the burrowand awakens the estivating fish.
Thanks for description - Animal life club