Lungfish

[[Image:Lungfish.jpg|thumb|165px|Top-bottom: South American, African and Australian lungfish.]]{{evolution}}
The '''lungfish''' are an example of the kind of life forms that [[creationism|creationist]]s are very quiet about. They rant and rave about a lack of [[transitional forms|intermediate forms]] between fish and land animals, sometimes with ridiculous statements like "I've never seen a half-fish half-cow". Lungfish are able to breathe with their lung and can live out of water for fairly long periods. They also use their lungs to obtain a continuous oxygen supply while they sit out the dry period under exposed mudbanks. 

In modern times, humans have classified lungfish in the class [[Sarcopterygii]], subclass '''Dipnoi''' ("two lungs"), further dividing them into two orders, Ceratodontiformes ("horn teeth forms") for the Australian lungfish, ''Neoceratodus forsteri'' (which has only one lung), and Lepidosireniformes ("scaly salamander forms") for the African and South American lungfish (genus ''Protopterus'', and ''Lepidosiren paradoxa'', respectively). How the lungfishes classify humans remains a mystery, so far.

Note: Although in some countries they are legal or quasi-legal as pets, Australian and African lungfishes are very fierce omnivores. Do not attempt to let them co-inhabit with other fishes, or provoke with anything valuable such as a limb.

==Living fossils==
Lungfish are [[living fossil]]s, similar in form to previous sarcoptergiian fish from the [[Devonian]] period onward (most sarcoptergiians are long extinct).<ref>[http://www.ucmp.berkeley.edu/vertebrates/sarco/sarcopterygii.html Introduction to the Sarcopterygii from fins to legs…]</ref> There are 6 surviving species in three living genera; the South American and African species are similar, with thin, flexible fins, while the [[Australia|Australian]] Lungfish has bony fins, giving it a superficial resemblance to the [[coelacanth]], the lungfishes' nearest non-[[tetrapod]] relative. The distribution of lungfish were once thought to be (and some still think it so) evidence for [[continental drift]], in that the ranges of the living species were due to vicariance (i.e., where a taxon's distribution is determined by the movement of continents) due to the break up of Gondwana during the Mesozoic.  However, due to further in-depth studies of the distribution of Post-Paleozoic lungfish fossils in the ancient continents of [[Pangaea]], and Laurasia, in addition to Gondwanaland, the distribution of "modern" lungfish actually represents the final strongholds of a 225 million or so year old, continents-spanning dynasty.

The African (''Protopterus annectens'') and South American (''Lepidosiren paradoxa'') lungfish can use their fins to "walk" along the surface of the substrate in a manner similar to the way tetrapods use their limbs on land,<ref>[http://www.bbc.co.uk/nature/16157835 Fish uses fins to walk and bound]</ref><ref>[http://www.pnas.org/content/early/2011/12/08/1118669109 Behavioral evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes]</ref> leaving tracks reminiscent of fossil tracks found in Devonian strata.
<ref>[http://arstechnica.com/science/news/2011/12/devonian-era-lungfish-may-have-faked-us-out-left-tetrapod-like-tracks.ars Devonian-era lungfish may have faked us out, left tetrapod-like tracks]</ref>

The Australian lungfish (''N. forsteri'') lives in brackish rivers and lakes and still has functional gills which supplement their lungs.<ref>[http://www.thefreedictionary.com/family+Ceratodontidae Family Ceratodontidae]</ref> This shows [[creationism|creationists]] are wrong when they argue that a fish could not survive without gills while its lungs were evolving. Fish did not lose their gills until their lungs had fully evolved. Some lungfish are more adapted to water and others to land.

The lungs of lungfish are alveolated (honeycombed) and vascularized, similar to land-dwelling tetrapods. Bichirs, a fish in the class [[Actinopterygii]], have gills as well as non-alveolated and vascularized lungs; they are obligate air breathers. Gars, another fish in the class Actinopterygii, have vascularized swim bladders that can function as lungs. Each of these three types of fish shows a step in the [[evolution]] of tetrapod lungs: vascularization of the swim bladder, obligate use of the swim bladder-turned lung, and alveolation of the swim bladder.

A recent study of bichirs found that when the juveniles were forced to live on land, they developed skeletal features that enabled them to walk better on land as adults than those that had been raised in water. These features matched what scientists had predicted would happen as fish evolved into tetrapods.<ref>[https://www.sciencenews.org/article/fish-reared-out-water-walks-better?mode=magazine&context=189135 A fish reared out of water walks better: A normally aquatic species raised on land suggests how ancient fish might have transitioned into terrestrial species]</ref>

==In a nutshell==
They are fish. With lungs. Accept it.

==See also==
*[[Fish that survive on land]]
*[[Amphistium and Heteronectes]]
*[[Tiktaalik]]
*[[Ichthyostega]]
*[[Transitional fossil]]s
*[[List of transitional fossils]]

==External links==
*[[Creation Wiki]]'s [http://creationwiki.org/Lungfish exceptionally detailed, evolution-rebutting view] on the lungfish

==References==
{{Reflist|2}}

{{Evonav}}

[[Category:Evolution]]
[[Category:Fish]]
[[Category:Transitional fossils]]
[[Category:Zoology]]

Categories: Evolution, Fish, Transitional fossils, Zoology