rhipidistia

{{short description|Clade of vertebrates}}

{{automatic taxobox

| name = Rhipidistians

| image =

File:Rhipidistia.png|220px

rect 0 0 500 330 Lungfish

rect 0 330 500 660 Mammal

rect 0 660 500 990 Reptile

rect 500 0 1000 330 Tiktaalik

rect 500 330 1000 660 Amphibian

rect 500 660 1000 990 Bird

| image_caption = Diversity of Rhipidistia

| fossil_range =
Early Devonian - Present, {{fossilrange|416|0}}

| taxon = Rhipidistia

| authority =

| subdivision_ranks = Subgroups

| subdivision = * Dipnomorpha

• {{extinct}}Porolepiformes
• Dipnoi (lungfish)
• Tetrapodomorpha

}}

Rhipidistia, also known as Dipnotetrapodomorpha,{{cite book|last=Joseph S.|first=Nelson|author-link=Joseph S. Nelson|title=Fishes of the World|url=https://books.google.com/books?id=exTV-GLnCB4C&pg=PA461|access-date=9 May 2015|date=19 May 2006|publisher=John Wiley & Sons|isbn=978-0-471-75644-6|page=461}} 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.{{cite web|title=Encyclopædia Britannica|url=http://www.britannica.com/EBchecked/topic/501438/Rhipidistia|access-date=3 April 2014}} 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.{{Cite book |last=Pough |first=F. Harvey |url=https://www.worldcat.org/oclc/1022979490 |title=Vertebrate Life |publisher=Oxford University Press |others=Christine M. Janis, Sergi López-Torres |year=2018 |isbn=978-1-60535-607-5 |edition=10th |location=New York |pages=123 |oclc=1022979490}}

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.{{Cite journal |last1=Zhu |first1=Min |last2=Ahlberg |first2=Per E. |date=2004 |title=The origin of the internal nostril of tetrapods |url=http://www.nature.com/articles/nature02843 |journal=Nature |language=en |volume=432 |issue=7013 |pages=94–97 |doi=10.1038/nature02843 |pmid=15525987 |bibcode=2004Natur.432...94Z |s2cid=4422813 |issn=0028-0836|url-access=subscription }}