AskDefine | Define lungfish

Dictionary Definition

lungfish n : air-breathing fish having an elongated body and fleshy paired fins; certain species construct mucus-lined mud coverings in which to survive drought [also: lungfishes (pl)]

User Contributed Dictionary

English

Noun

lungfish (plural lungfish or lungfishes)
  1. air-breathing fish, of the class Dipnoi, that have four limblike appendages instead of fins

Derived terms

Extensive Definition

Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best-known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Today, they live only in Africa, South America, and Australia. While vicariance would suggest this represents an ancient distribution limited to the Mesozoic supercontinent Gondwana, the fossil record suggests that advanced lungfish had a cosmopolitan freshwater distribution and that the current distribution of modern lungfish species reflects extinction of many lineages following the breakup of Pangea, Gondwana, and Laurasia.

Anatomy and morphology

All lungfish demonstrate an uninterrupted cartilaginous notochord and an extensively developed palatal dentition. The lungfish is a true carnivore. Basal lungfish groups may retain marginal teeth and an ossified braincase, but derived lungfish taxa, including all modern species, show a significant reduction in marginal bones and a cartilaginous braincase. The bones of the skull roof in primitive lungfish are covered in a mineralized tissue called cosmine, but in post-devonian lungfishes, the skull roof is subdermal and the cosmine covering is lost. All modern lungfish show significant reductions and fusions of the bones of the skull roof, and the specific bones of the skull roof show no homology to the skull roof bones of actinopterygiians or tetrapods.
The dentition of lungfish is conspicuously different from that of any other vertebrate group. Odontodes on the palate and lower jaws develop in a series of rows to form a fan-shaped occlusion surface. These odontodes then wear to form a uniform crushing surface. In several groups, including the modern lepidosireniformes, these ridges have been modified to form occluding blades.
The modern lungfishes have a number of larval features, which suggest paedomorphosis. They also demonstrate the largest genome among the vertebrates.
Modern lungfish all have an elongate body with fleshy paired pectoral and pelvic fins and a single unpaired caudal fin replacing the dorsal, caudal, and anal fin of most fishes.

Ecology and life history

Behavior

African and South American lungfish are capable of surviving seasonal desiccation of habitats by burrowing into mud and estivating throughout the dry season. Changes in physiology allow the lungfish to slow its metabolism to as little as 1/60th of the normal metabolic rate, and protein waste is converted from ammonia to less-toxic urea (normally, lungfish excrete nitrogenous waste as ammonia directly into the water). Burrowing is seen in at least one group of fossil lungfish, the Gnathorhizidae. It has been proposed both that burrowing is plesiomorphic for lungfish as well as that gnathorhizids are directly ancestral to modern Lepidosireniformes, but it is possible that the similarity is simply due to convergent evolution or parallel evolution. Lungfish can be extremely long-lived. The Queensland species lungfish at the Shedd Aquarium in Chicago has been part of the permanent live collection since 1933.

Taxonomy

The relationship of lungfishes to the rest of Osteichthyes is well-understood:
The relationship 'among' lungfishes to each other is significantly more difficult to resolve. While Devonian lungfish retain enough ossification of the endocranium to determine relationships, post-Devonian lungfish are represented entirely by skull roofs and teeth, as the rest of the skull is cartilaginous. Additionally, many of the taxa that have been identified may not be monophyletic. Current phylogenetic studies support the following relationships of major lungfish taxa:
Class Osteichthyes Subclass Sarcopterygii Order Dipnoi
,--†Family Diabolichthyidae | ,--†Family Uranolophidae | | __,--†Family Speonesydrionidae '-|-| '--†Family Dipnorhynchidae | ,--†Family Stomiahykidae '----|___ ,--†Family Chirodipteridae | '-|--†Family Holodontidae |------†Family Dipteridae | __,--†Family Fleurantiidae '-| '--†Family Rhynchodipteridae '--†Family Phaneropleuridae | ,--†Family Ctenodontidae '-| ,--†Family Sagenodontidae '-|--†Family Gnathorhizidae '--Order Ceratodontiformes |--†family Asiatoceratodontidae |--†Family Ptychoceratodontidae |--Family Ceratodontidae | '--†Genus Ceratodus | '--†Genus Metaceratodus '--Family Neoceratodontidae | '--†Genus Mioceratodus | '--Genus Neoceratodus - Queensland lungfish '--Order Lepidosireniformes '--Family Lepidosirenidae - South American lungfish '--Family Protopteridae - African lungfish

References

  • Ahlberg, PE, Smith, MM, and Johanson, Z, (2006). Developmental plasticity and disparity in early dipnoan (lungfish) dentitions. Evolution and Development 8(4):331-349.
  • Palmer, Douglas, Ed. The Simon & Schuster Encyclopedia of Dinosaurs & Prehistoric Cretures. A Visual Who's Who of Prehistoric Life. Pg. 45. Great Britain: Marshall Editions Developments Limited. 1999.
  • Schultze, HP, and Chorn, J., (1997). The Permo-Herbivorus genus Sagenodus and the beginning of modern lungfish. Contributions to Zoology 61(7):9-70.
lungfish in Bosnian: Ribe dvodihalice
lungfish in Catalan: Dipnou
lungfish in Danish: Lungefisk
lungfish in German: Lungenfische
lungfish in Estonian: Kopskalad
lungfish in Spanish: Dipnoi
lungfish in Esperanto: Pulmofiŝoj
lungfish in French: Dipnoi
lungfish in Korean: 폐어류
lungfish in Italian: Dipnoi
lungfish in Lithuanian: Dvikvėpės žuvys
lungfish in Hungarian: Gőtehalalakúak
lungfish in Dutch: Longvissen
lungfish in Japanese: ハイギョ
lungfish in Norwegian: Lungefisker
lungfish in Occitan (post 1500): Dipnoi
lungfish in Polish: Dwudyszne
lungfish in Portuguese: Dipnóicos
lungfish in Russian: Двоякодышащие
lungfish in Slovak: Dvojdyšníky
lungfish in Serbian: Рибе дводихалице
lungfish in Finnish: Keuhkokalat
lungfish in Swedish: Lungfiskar
lungfish in Thai: ปลาปอด
lungfish in Vietnamese: Cá phổi
lungfish in Turkish: Akciğerli balıklar
lungfish in Ukrainian: Дводишні
lungfish in Chinese: 肺鱼类
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