Author(s): beblondie (Anne)
Edited, Arranged, and Referenced by Xander (Alexander Eng)
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Lungfish Evolution and Natural History
The Dipnoi are a subclass of sarcopterygiian fish, are are commonly known as the lungfish.They are orginaly believed to have evolved in marine enviroments during the devonian period(400 mya).
These early lungfish consisted of as many as 10 families, 50 genera and some 100 species according to fossil records.
These early lungfish looked quite different than today's remaining species. Early lungfish had dual dorsal fins, fleshy paired fins, and showed no teeth on the jaw bones but instead had teeth fused to heavy tooth plates used for crushing prey. Later as they moved into freshwater enviroments many changes occured the first dorsal fin dissapeared and the remaining dorsal fused with the cadual and anal fin forming a symetrical tail and some bones were replaced with cartillage.
During the Carboniferous period (290mya) many of the lungfish species disappear and are known only from Fossils. Lungfish burrows of Gnathorhiza have been found in rocks as old as the Permian, with the lungfish still inside, and older (empty) burrows are known from the Carboniferous and Devonian. The oldest fossil dipnoan is Diabolichthyes, from the Lower Devonian of Yunnan, China. It is not clear whether this particular fish was marine or lived in freshwater like modern lungfish, but both marine and freshwater fossils of other groups are known.This indicates estavation occured as early as the Devonian period.
Fossil records show that Ceratodontidae (Austrailian) family appeared during the Triassic period (245mya)and were widespread by the Mezzoic period (65 mya), with fossil remains being found on all continents. Some species being as large as 16ft in length and weighing as much as 200 pluslbs. The "modern"genus neoceratodus of the Australian lungfish arose in the early Cretaceous period (145mya) originally consisted of 7 species, of which only 1 - Neoceratodus forsteri - still exists today and is now confined to a small section of southern Queensland in slow moving portions of the Burnett and Mary river systems.
The Lepidosirenid lungfish of Africa and South America can be dated back to the Carboniferous period (290mya)the existing members of the genera did not appear until the Eocene period(54mya) and the Miocene period(23mya)on the same continents where they occur today.