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Lobe-finned fishes
Temporal range:
From top to bottom and left to right, examples of sarcopterygians: .
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Euteleostomi
Clade: Sarcopterygii
Romer, 1955

Sarcopterygii (

extant group), evolved from certain sarcopterygians; under a cladistic
view, tetrapods are themselves considered a subgroup within Sarcopterygii.

The known extant non-tetrapod sarcopterygians include two species of coelacanths and six species of lungfishes.


Guiyu oneiros, the earliest-known bony fish, lived during the Late Silurian, 419 million years ago).[1] It has the combination of both ray-finned and lobe-finned features, although analysis of the totality of its features places it closer to lobe-finned fish.[2][3][4]

Early lobe-finned fishes are

derived from these fins. Sarcopterygians also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of actinopterygians (ray-finned fish). The braincase of sarcopterygians primitively has a hinge line, but this is lost in tetrapods and lungfish. Many early sarcopterygians have a symmetrical tail. All sarcopterygians possess teeth covered with true enamel

Most species of lobe-finned fishes are extinct. The largest known lobe-finned fish was

extant (living) species, the coelacanths and the lungfishes, the largest species is the West Indian Ocean coelacanth, reaching 2 m (6 ft 7 in) in length and weighing up 110 kg (240 lb). The largest lungfish is the African lungfish which can reach 2 m (6.6 ft) in length and weigh up to 50 kg (110 lb).[8][9]


Taxonomists who subscribe to the cladistic approach include the grouping Tetrapoda within this group, which in turn consists of all species of four-limbed vertebrates.



The classification below follows Benton (2004),[11] and uses a synthesis of rank-based Linnaean taxonomy and also reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank.[11]

Actinistia, coelacanths, are a subclass of lobe-finned fishes, all but two of which are fossil species. The subclass Actinistia contains the coelacanths, including the two living coelacanths: the West Indian Ocean coelacanth and the Indonesian coelacanth.
Queensland lungfish
Dipnoi, lungfish, also known as salamanderfish,[12] are a subclass of freshwater fish. Lungfish are best known for retaining characteristics primitive within the bony fishes, including the ability to breathe air, and structures primitive within the lobe-finned fishes, including the presence of lobed fins with a well-developed internal skeleton. Today, lungfish 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 advanced lungfish had a widespread freshwater distribution and the current distribution of modern lungfish species reflects extinction of many lineages following the breakup of Pangaea, Gondwana, and Laurasia.
Tiktaalik restoration (side view) by ObsidianSoul 02.png
Advanced tetrapodomorph Tiktaalik
Tetrapodomorpha, tetrapods and their extinct relatives, are a clade of vertebrates consisting of tetrapods (four-limbed vertebrates) and their closest sarcopterygian relatives that are more closely related to living tetrapods than to living lungfish.[13] Advanced forms transitional between fish and the early labyrinthodonts, like Tiktaalik, have been referred to as "fishapods" by their discoverers, being half-fish, half-tetrapods, in appearance and limb morphology. The Tetrapodomorpha contain the crown group tetrapods (the last common ancestor of living tetrapods and all of its descendants) and several groups of early stem tetrapods, and several groups of related lobe-finned fishes, collectively known as the osteolepiforms. The Tetrapodamorpha minus the crown group Tetrapoda are the stem tetrapoda, a paraphyletic unit encompassing the fish to tetrapod transition. Among the characters defining tetrapodomorphs are modifications to the fins, notably a humerus with convex head articulating with the glenoid fossa (the socket of the shoulder joint). Tetrapodomorph fossils are known from the early Devonian onwards, and include Osteolepis, Panderichthys, Kenichthys, and Tungsenia.[14]
Queensland lungfish


The cladogram presented below is based on studies compiled by Janvier et al. (1997) for the Tree of Life Web Project,[15] Mikko's Phylogeny Archive[16] and Swartz (2012).[17]





Styloichthys changae Zhu & Yu, 2002





?†Tungsenia paradoxa Lu et al., 2012

Kenichthys campbelli Chang & Zhu, 1993








Tinirau clackae
Swartz, 2012

Platycephalichthys Vorobyeva, 1959


Panderichthys rhombolepis Gross, 1941




Metaxygnathus denticulus Campbell & Bell, 1977

Ventastega curonica


Life restoration of Sparalepis tingi and other fauna from the Silurian of Yunnan


Evolution of lobe-finned fishes
In Late Devonian vertebrate speciation, descendants of pelagic lobe-finned fish—like Eusthenopteron
— exhibited a sequence of adaptations: Descendants also included pelagic lobe-finned fish such as coelacanth species.
Tooth from the sarcopterygian Onychodus from the Devonian of Wisconsin

Lobe-finned fishes (sarcopterygians) and their relatives the ray-finned fishes (


In the Early Devonian (416–397 Ma), the sarcopterygians split into two main lineages: the

open (pelagic) oceans

The Rhipidistians, whose ancestors probably lived in the oceans near the river mouths (estuaries), left the ocean world and migrated into freshwater habitats. In turn, they split into two major groups: lungfish and the tetrapodomorphs. Lungfish radiated into their greatest diversity during the Triassic period; today fewer than a dozen genera remain. They evolved the first proto-lungs and proto-limbs, adapting to living outside a submerged water environment by the middle Devonian (397–385 Ma).

Hypotheses for means of pre-adaption

There are three major hypotheses as to how lungfish evolved their stubby fins (proto-limbs).

Shrinking waterhole
The first, traditional explanation is the "shrinking waterhole hypothesis", or "desert hypothesis", posited by the American paleontologist Alfred Romer, who believed that limbs and lungs may have evolved from the necessity of having to find new bodies of water as old waterholes dried up.[21]
Inter-tidal adaption
Niedźwiedzki, Szrek, Narkiewicz, et al. (2010)
Zachełmie tracks in Zachełmie, Świętokrzyskie Voivodeship, Poland, the oldest discovered fossil evidence of tetrapods.[22][23]
Woodland swamp adaption
Retallack (2011)[24] proposed a third hypothesis is dubbed the "woodland hypothesis": Retallack argues that limbs may have developed in shallow bodies of water, in woodlands, as a means of navigating in environments filled with roots and vegetation. He based his conclusions on the evidence that transitional tetrapod fossils are consistently found in habitats that were formerly humid and wooded floodplains.[21][24]
Habitual escape onto land
A fourth, minority hypothesis posits that advancing onto land achieved more safety from predators, less competition for prey, and certain environmental advantages not found in water—such as oxygen concentration,[27] and temperature control[29]—implying that organisms developing limbs were also adapting to spending some of their time out of water. However, studies have found that sarcopterygians developed tetrapod-like limbs suitable for walking well before venturing onto land.[32] This suggests they adapted to walking on the ground-bed under water before they advanced onto dry land.

History through to the end-Permian extinction

The first tetrapodomorphs, which included the gigantic rhizodonts, had the same general anatomy as the lungfish, who were their closest kin, but they appear not to have left their water habitat until the late Devonian epoch (385–359 Ma), with the appearance of tetrapods (four-legged vertebrates). Tetrapods are the only tetrapodomorphs which survived after the Devonian.

Non-tetrapod sarcopterygians continued until towards the end of Paleozoic era, suffering heavy losses during the Permian–Triassic extinction event (251 Ma).

See also


  1. ^ The Osteolepida taxa were not addressed by Ahlberg & Johanson (1998).[citation needed]


  1. ^
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  2. ^ Zhu, M.; Zhao, W.; Jia, L.; Lu, J.; Qiao, T.; Qu, Q. (2009). "The oldest articulated osteichthyan reveals mosaic gnathostome characters". Nature. 458 (7237): 469–474.
    S2CID 669711
  3. ^ Coates, M.I. (2009). "Palaeontology: Beyond the age of fishes". Nature. 458 (7237): 413–414.
    S2CID 4384525
  4. ^ "Pharyngula – Guiyu oneiros". Science Blogs (blog). 1 April 2009. Archived from the original on 9 March 2012.
  5. ^ Clack, J.A. (2002). Gaining Ground. Indiana University.
  6. ^ Kardong, Kenneth V. (1998). Vertebrates: Comparative anatomy, function, evolution (second ed.). USA: McGraw-Hill.
  7. ^ Clack, J.A. (2009). "The fin to limb transition: New data, interpretations, and hypotheses from paleontology and developmental biology". Annual Review of Earth and Planetary Sciences. 37 (1): 163–179. .
  8. ^ Froese, Rainer, and Daniel Pauly, eds. (2009). "Lepidosirenidae" in FishBase. January 2009 version.
  9. ^ "Protopterus aethiopicus". Lung fishes. Archived from the original on 3 August 2011.
  10. ^ Nelson, Joseph S. (2006). .
  11. ^ a b Benton, M.J. (2004). Vertebrate Paleontology (3rd ed.). Blackwell Science.
  12. ^ Haeckel, Ernst Heinrich Philipp August (1892). Lankester, Edwin Ray; Schmitz, L. Dora (eds.). The History of Creation, or, the Development of the Earth and Its Inhabitants by the Action of Natural Causes (8th, German ed.). D. Appleton. p. 289. A popular exposition of the doctrine of evolution in general, and of that of Darwin, Goethe, and Lamarck in particular.
  13. ^ Amemiya, C.T.; Alfoldi, J.; Lee, A.P.; Fan, S.H.; Philippe, H.; MacCallum, I.; Braasch, I.; et al. (2013). "The African coelacanth genome provides insights into tetrapod evolution".
    PMID 23598338
  14. ^ Lu, Jing; Zhu, Min; Long, John A.; Zhao, Wenjin; Senden, Tim J.; Jia, Liantao; Qiao, Tuo (2012). "The earliest known stem-tetrapod from the lower Devonian of China". Nature Communications. 3: 1160.
    PMID 23093197
  15. ^ Janvier, Philippe (1 January 1997). "Vertebrata: Animals with backbones". (Version 01 January 1997 (under construction) ed.). The Tree of Life Web Project.
  16. ^ Haaramo, Mikko (2003). "Sarcopterygii". Mikko's Phylogeny Archive. University of Helsinki. Retrieved 4 November 2013.
  17. ^ Swartz, B. (2012). "A marine stem-tetrapod from the Devonian of western North America". PLOS ONE. 7 (3): e33683.
    PMID 22448265
  18. ^ Choo, Brian; Zhu, Min; Qu, Qingming; Yu, Xiaobo; Jia, Liantao; Zhao, Wenjin (8 March 2017). "A new osteichthyan from the late Silurian of Yunnan, China". PLOS ONE. 12 (3): e0170929.
    PMID 28273081
  19. ^ "Ancient southern China fish may have evolved prior to the 'Age of Fish'". (Press release). PLoS. March 2017. Archived from the original on 8 March 2017. Retrieved 11 March 2017.
  20. ^ Benton 2005.
  21. ^ a b "Fish-tetrapod transition got a new hypothesis in 2011". Science 2.0. 27 December 2011. Retrieved 2 January 2012.
  22. ^ a b Niedźwiedzki, Grzegorz; Szrek, Piotr; Narkiewicz, Katarzyna; Narkiewicz, Marek; Ahlberg, Per E. (2010). "Tetrapod trackways from the early Middle Devonian period of Poland".
    S2CID 4428903
  23. ^ Barley, Shanta (6 January 2010). "Oldest footprints of a four-legged vertebrate discovered". New Scientist. Retrieved 3 January 2010.
  24. ^ a b
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  25. ^ Carroll, R.L.; Irwin, J.; Green, D.M. (2005). "Thermal physiology and the origin of terrestriality in vertebrates". Zoological Journal of the Linnean Society. 143 (3): 345–358. .
  26. ^ a b Hohn-Schulte, B.; Preuschoft, H.; Witzel, U.; Distler-Hoffmann, C. (2013). "Biomechanics and functional preconditions for terrestrial lifestyle in basal tetrapods, with special consideration of Tiktaalik roseae". Historical Biology. 25 (2): 167–181.
    S2CID 85407197
  27. ^ Carroll, Irwin, & Green (2005),[25] cited in[26]
  28. ^ Clack, J.A. (2007). "Devonian climate change, breathing, and the origin of the tetrapod stem group" (PDF). Integrative and Comparative Biology. 47 (4): 1–14. ]
  29. ^ Clack (2007),[28] cited in[26]
  30. ^ King, H.M.; Shubin, N.H.; Coates, M.I.; Hale, M.E. (2011). "Behavioural evidence for the evolution of walking and bounding before terrestriality in sarcopterygian fishes". Proceedings of the National Academy of Sciences USA. 108 (52): 21146–21151.
    PMID 22160688
  31. ^ Pierce, S.E.; Clack, J.A.; Hutchinson, J.R. (2012). "Three-dimensional limb joint mobility in the early tetrapod Ichthyostega".
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  32. ^ King (2011),[30] cited in[31]