Lungfish
| Lungfish | ||||||||||||
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Australian lungfish ( Neoceratodus forsteri ) |
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| Scientific name | ||||||||||||
| Dipnoi | ||||||||||||
| Müller , 1844 |
The lung fish (Dipnoi) are a subclass of the bony fish (Osteichthyes), which occurs with six recent species in Africa, South America and Australia. Their closest living relatives are the terrestrial vertebrates (Tetrapoda), followed by the coelaceans (Crossopterygiformes). The scientific name goes back to the masculine plural form of the Greek artificial word δίπνους , dípnous and means "double breathers" because the lungfish have gills to breathe in the water and lungs to breathe air from the water surface. The German name Lungfische is derived from the fact that they have a simply built lung.
Discovery story
Fossil lungfish from the Old Red sandstone have been known for more than 200 years. The South American lungfish was the first living species to be discovered by the Austrian zoologist Johann Natterer in 1836 and described as a reptile by his colleague Leopold Fitzinger in 1837 , who noticed the lungs and the unusual position of the outer nostrils near the upper lip . The first scientists to see live lungfish couldn't believe they were looking at fish. Fitzinger had no doubt that the South American lungfish was a reptile, especially since the “reptiles” were not yet clearly divided into amphibians and reptiles. The scientific name Lepidosiren means scaled newt , and this term remained in German for a long time, e.g. B. in Brehm's animal life .
The British zoologist Richard Owen , who described the African lungfish in 1839 , then realized that the animals must be fish. The Australian lungfish was finally found in Queensland in 1870 , 32 years after its close Triassic cousin Ceratodus was described by the Swiss paleontologist Louis Agassiz using its dental plates. Albert Günther published an exact anatomical description of the Australian lungfish in 1871 and confirmed the fish nature of the animals.
anatomy
The recent lung fish are 44 centimeters to 1.70 meters long. In all six species the dorsal fin, the protocerke caudal fin and the anal fin have grown together to form a fin edge . In contrast, the Devonian lungfish had clearly separated dorsal, anal and caudal fins that were still heterocerk . The Australian lungfish have pectoral and ventral fins that are supported by a partially ossified and muscular skeleton . In the remaining five species, the paired fins are transformed into thread-like organs without fin rays.
The Australian lungfish has large, diamond-shaped scales, the scales of the other species are small and are deeply embedded in a glandular epidermis.
The lung fish lungs are an organ in the intestine that is homologous to the swim bladder . The Australian lungfish have a single lung that lies above the intestine. The remaining species have paired lungs that lie ventrally. Typically lungfish rise to the surface of the water every 30 to 60 minutes to breathe air.
The African and South American lungfish have outer gill leaflets as larvae, which then regress. Some species rely on air breathing . If they are held underwater for too long, they will suffocate - a very unusual property for fish. They primarily use their gills to release carbon dioxide , to regulate the acid-base balance and to release nitrogenous waste products .
The body of the lungfish is elongated, outwardly there is no difference between male and female animals. A specialty of the Dipnoi is the lymphatic system , which they share with the tetrapods, but not with the other fish - so it must have arisen in the Devonian , only after the separation of the bony fish into Actino (ray fins) and Sarcopterygii (meat fins).
Way of life
Lungfish are very lazy animals that mainly inhabit small standing or slowly flowing bodies of water. Only the Ethiopian lungfish ( Protopterus aethiopicus ) also inhabit large lakes, e.g. B. Lake Tanganyika . Lungfish feed on a carnivorous diet and eat slow bottom fish, mussels , snails , worms, crustaceans and insect larvae .
It has been reported that African lungfish can encapsulate themselves in a shell made of their own mucus and mud for up to four years. To do this, they dig themselves into the mud and secrete slime. This solidifies and lines the passage dug in the mud. A hole is left near the mouth through which the lungs can breathe. During this time they live on their muscle tissue and store their waste products, which they remove the water from and return to their circulation . They curl up and hold their tails over their eyes to protect them from dehydration. After such a phase, they look like dried fish and it takes several hours before they can move again.
Unlike their relatives, the South American lungfish ( Lepidosiren ) and the African lungfish ( Protopterus ), Australian lungfish ( Neoceratodus ) can not encapsulate themselves in the mud when it is dry and survive there.
Reproduction
Lungfish reproduce oviparously and lay up to 5000 eggs per nest. The eggs of the Australian and African lungfish are 3 to 4 mm in diameter, those of the South American lung fish are 6 to 7 mm larger. The eggs are coated in a gelatinous substance in the Müller passage . African and South American lungfish build horizontal tunnels in the waterfront where the eggs are laid. The Australian lungfish sticks them to aquatic plants. Its larvae hatch after 25 to 30 days. They have no outer gills, while those of the other two genera have three or four outer gill tufts.
evolution
In the ancient times ( Paleozoic ), lungfish were common both in the sea and in freshwater. The first lungfish are known from the geological age of the Devonian from the Chinese Yunnan province. The first, albeit empty, fossil mud capsules also date from this time . Lungfish preserved in such are only known from the Permian .
Most of the species became extinct in the great mass extinction of the Permian Triassic boundary . Only two groups survived that have survived to this day. The Neoceratodontidae, which are only represented by one species today, spread throughout the world in the Mesozoic.
The relatively close relatives of the coelacanth and lungfish, the Rhipidistia , are often regarded in paleontology as the ancestors of the first terrestrial vertebrates (Tetrapoda). The structure of their skeleton is similar to Ichthyostega , a fossil that is considered to be one of the first amphibians and therefore a land vertebrate. Tiktaalik is a transitional form between fish-like flesh-flippers and land vertebrates.
A number of common features speak for a close relationship between the lungfish and the terrestrial vertebrates, in particular the structure of the skull, the approach of separating oxygen-rich blood from the lungs and oxygen-poor blood from the body and the four roughly equal-sized extremities that are shaped and Position to match the legs of terrestrial vertebrates.
In 1996 an analysis was published according to which the genetic material of the lungfish is close to the phylogenetic root of all vertebrates . The living lungfish species have the most complex genome of all known living things. Their genetic makeup is sometimes more than twenty times more extensive than that of a person.
Genome size
The South American lungfish has the largest animal genome known to date with 80 picograms (7.84 × 10 10 base pairs ) . Older, but probably less precise, studies show even larger genomes, around 133 picograms, which were found in the African species of Ethiopian lungfish.
Systematics
The recent lung fish and their immediate ancestors are summarized in the superorder Ceratodontimorpha and the order Ceratodontiformes. They occur in six species in Africa , Australia and South America . They are divided into three families and three genera , with four representatives of one genus in Africa:
- Order Ceratodontiformes
- Family Ceratodontidae
- Family Neoceratodontidae
- Australian lungfish ( Neoceratodus forsteri )
- Order Lepidosireniformes
- Family Lepidosirenidae
- South American lungfish ( Lepidosiren paradoxa )
- African lungfish family (Protopteridae)
- Ethiopian lungfish ( Protopterus aethiopicus )
- East African lungfish ( Protopterus amphibius )
- West African lungfish ( Protopterus annectens )
- Congo lungfish ( Protopterus dolloi )
- Family Lepidosirenidae
The phylogenetic relationships of the species living today can be seen in the following diagram:
| Lungfish (Dipnoi) |
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literature
- Wilfried Westheide , Reinhard Rieger : Special Zoology Part 2: Vertebrate or Skull Animals , 1st edition, Spectrum Academic Publishing House, Heidelberg • Berlin, 2004, ISBN 3-8274-0307-3
- Joseph S. Nelson : Fishes of the World , John Wiley & Sons, 2006, ISBN 0-471-25031-7
- Kurt Fiedler: Textbook of Special Zoology, Volume II, Part 2: Fish , Gustav Fischer, Jena 1991, ISBN 3-334-00339-6
- John A. Long: The Rise of Fishes . Johns Hopkins University Press, 1995, ISBN 0-8018-4992-6
- Günther Sterba : The world's freshwater fish. 2nd Edition. Urania, Leipzig / Jena / Berlin 1990, ISBN 3-332-00109-4 .
Individual evidence
- ^ John A. Long, 1995, pp. 162-163.
- ↑ Westheide, Rieger, 2004, page 295
- ^ AE Vinogradov: Genome size and chromatin condensation in vertebrates. Chromosoma 113, 2005; Pages 362-369.
- ^ TR Gregory: Animal Genome Size Database. 2005
Web links
- Dipnoi on Palæos
- University of California Museum of Paleontology Introduction to the Dipnoi
- Mikko's Phylogeny Archive Dipnoiformes (in English / Finnish)