Rhipidistia

Life-forms

Superregnum: Eukaryota
Cladus: Unikonta
Cladus: Opisthokonta
Cladus: Holozoa
Regnum: Animalia
Subregnum: Eumetazoa
Cladus: Bilateria
Cladus: Nephrozoa
Superphylum: Deuterostomia
Phylum: Chordata
Subphylum: Vertebrata
Infraphylum: Gnathostomata
Megaclassis: Osteichthyes
Cladus: Sarcopterygii
Cladus: Rhipidistia
Cladi: Dipnomorpha – Tetrapodomorpha
Genera incertae sedis: †Styloichthys
Name

Rhipidistia Cope, 1887 sensu Cloutier & Ahlberg, 1996
References
Primary references

Cope, E.D. 1887. Geology and palaeontology. The American Naturalist 21: 1104–1019. Reference page.
Cloutier, R.C. & Ahlberg, P.E. 1996. Morphology, characters, and the interrelationships of basal sarcopterygians. Pp. 445–479 in: Stiassny, M.L.J., Parenti, L.R. & Johnson, G.D. (eds.): Interrelationships of Fishes. San Diego (Academic Press). Reference page.

Rhipidistia, also known as Dipnotetrapodomorpha,[1] is a clade of lobe-finned fishes which includes the tetrapods and lungfishes. Rhipidistia formerly referred to a subgroup of Sarcopterygii consisting of the Porolepiformes and Osteolepiformes, a definition that is now obsolete.[2] However, as cladistic understanding of the vertebrates has improved over the last few decades, a monophyletic Rhipidistia is now understood to include the whole of Tetrapoda and the lungfishes.

Rhipidistia includes Porolepiformes and Dipnoi. Extensive fossilization of lungfishes has contributed to many evolutionary studies of this group. Evolution of autostylic jaw suspension, in which the palatoquadrate bone fuses to the cranium, and the lymph pumping "lymph heart" (later lost in mammals and flying birds), are unique to this group. Another feature shared by lungfish and tetrapods is the divided atrium.[3]

The precise time at which the choana of tetrapods evolved is debated, with some considering early rhipidistians as the first choanates. The feature is also present in modern lungfish but is probably a case of convergent evolution. The basal stem-lungfish Diabolepis did not possess it. Instead, it had four nostrils (two anterior and two posterior) like most fish. However, its posterior nares are very close to the lip, meaning a ventral 'displacement' of the posterior nostril can be considered a synapomorphy of the lungfish-tetrapod clade. The complete choana then seems to have developed independently in the two surviving clades.[4]
Etymology

Rhipidistia is from Ancient Greek ῥιπίδιον (rhipídion, "small bellows")

Dipnotetrapodomorpha is from the Greek δίπνοος (dipnoos) with two breathing structures; and from δι- twice and πνοή breathing, breath; and from ancient Greek τετρα- (tetra-), combining form of the numeral τέτταρες (tettares), and ancient Greek -ποδ- (-pod-)the combining form of πούς (pous, foot); and ancient Greek -μορϕος (-morphos), combining form of μορϕή (morph) physical shape.
Relationships

The cladogram presented below is based on studies compiled by Philippe Janvier and others for the Tree of Life Web Project,[5] and Swartz 2012.[6]

Sarcopterygii

†Onychodontidae Actinistia (coelacanths) Rhipidistia †Styloichthys Dipnomorpha †Porolepiformes Dipnoi (lungfishes) Tetrapodomorpha ?†Tungsenia †Kenichthys †Rhizodontiformes ?†Thysanolepidae †Canowindridae †Osteolepiformes Eotetrapodiformes †Tristichopteridae †Tinirau †Platycephalichthys Elpistostegalia †Panderichthys †Elpistostegidae Stegocephalia †Elginerpetontidae †Metaxygnathus †Ventastega Tetrapoda

References

Joseph S., Nelson (19 May 2006). Fishes of the World. John Wiley & Sons. p. 461. ISBN 978-0-471-75644-6. Retrieved 9 May 2015.
"Encyclopædia Britannica". Retrieved 3 April 2014.
Pough, F. Harvey (2018). Vertebrate Life. Christine M. Janis, Sergi López-Torres (10th ed.). New York: Oxford University Press. p. 123. ISBN 978-1-60535-607-5. OCLC 1022979490.
Zhu, Min; Ahlberg, Per E. (2004). "The origin of the internal nostril of tetrapods". Nature. 432 (7013): 94–97. Bibcode:2004Natur.432...94Z. doi:10.1038/nature02843. ISSN 0028-0836. PMID 15525987. S2CID 4422813.
Janvier, Philippe. 1997. Vertebrata. Animals with backbones. Version 01 January 1997 (under construction). http://tolweb.org/Vertebrata/14829/1997.01.01 in The Tree of Life Web Project, http://tolweb.org/
Swartz, B. (2012). "A marine stem-tetrapod from the Devonian of Western North America". PLOS ONE. 7 (3): e33683. Bibcode:2012PLoSO...733683S. doi:10.1371/journal.pone.0033683. PMC 3308997. PMID 22448265.