Rhipidistia

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.

Rhipidistians
Temporal range:
Early Devonian - Present,
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Sarcopterygii
Clade: Rhipidistia
Subgroups

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
  1. 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.
  2. "Encyclopædia Britannica". Retrieved 3 April 2014.
  3. 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.
  4. 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.
  5. 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/
  6. 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.


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