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African And South American Lungfish, Australian Lungfish

Bony fish are divided into two major groups: rayfinned and fleshy-finned fish. The fleshy-finned fish are further subdivided into two orders: the lungfish, or Dipnoi, and the lobe-finned fish, or Crossopterygii. Although crossopterygian fish are the group that is thought to be close to the ancestors of the land vertebrates, lungfish also display many of these characteristics. In the early stages of development, lungfish resemble a frog-like amphibian, providing evidence of close association with land forms. However, despite the critical presence of lungs, other features, such as the fusion of the teeth into bony plates, and the solid union of the jaw with the skull (which does not occur in early amphibians) make such a direct link with amphibians unlikely.

Lungfish have changed little over the past 400 million years, and so might be regarded as living fossils. Three living genera of lungfish are recognized today: Neoceratodus in the Mary and Burnett Rivers of southeast Queensland, Australia; Lepidosiren in the ParanNBSP and Amazon River systems of South America; and Protopterus in sub-Saharan Africa ranging from the Nile in Sudan southward to Senegal in West Africa to the Zambezi River system in southern Africa.

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Science EncyclopediaScience & Philosophy: Linear expansivity to Macrocosm and microcosm