| Rhipidistians | |
|---|---|
 | |
| Diversity of Rhipidistia | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Sarcopterygii |
| Clade: | Rhipidistia |
| Subgroups | |
| |
Rhipidistia, also known asDipnotetrapodomorpha,[1] is a clade oflobe-finned fishes which includes thetetrapods andlungfishes. Rhipidistia formerly referred to a subgroup ofSarcopterygii consisting of thePorolepiformes andOsteolepiformes, 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 ofTetrapoda and thelungfishes.
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 thelymph pumping "lymph heart" (later lost inmammals and flyingbirds), are unique to this group. Another feature shared by lungfish and tetrapods is the dividedatrium.[3]
The precise time at which thechoana 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 ofconvergent evolution. The basal stem-lungfishDiabolepis 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]
The word "Rhipidistia" is fromAncient Greek:ῥιπίδιον,romanized: rhipídion,lit. 'smallbellows'.
The word "Dipnotetrapodomorpha" is fromGreek:δίπνοος,romanized: dipnoos,lit. 'with two breathing structures' (fromδι- meaning "twice", andπνοή meaning "breathing, breath"); from Ancient Greek:τετρα-,romanized: tetra-,lit. 'four', thecombining form of the numeralτέτταρες (tettares); from Ancient Greek:-ποδ-,romanized: -pod-, the combining form ofπούς (pous) meaning "foot"; and from Ancient Greek:-μορφος,romanized: -morphos, the combining form ofμορφή (morph) meaning "physical shape".
The cladogram presented below is based on studies compiled by Philippe Janvier and others for theTree of Life Web Project,[5] and Swartz 2012.[6]
| Sarcopterygii |
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| Forerunners | 
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| Jawless fish |
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| Jawed fish |
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| Lists | |||||||||||||
| Related | |||||||||||||
† extinct | |||||||||||||
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