Iniidae

{{Short description|Family of dolphins}}{{Copy edit|date=June 2025}}{{Automatic taxobox | fossil_range = [[Miocene]]-[[Holocene]] | image = Inia.jpg | image_caption = An [[Amazon river dolphin]] at [[Duisburg Zoo]] holding an Armored catfish in the mouth. | image2 = Amazon river dolphin size.svg | image2_caption = Size compared to an average human | taxon = Iniidae | authority = [[John Edward Gray|Gray]], 1846 | subdivision_ranks = Genera | subdivision = ''[[Inia]]'' }}

'''Iniidae''' is a [[Family (taxonomy)|family]] of [[river dolphin]]s containing one living genus, ''[[Inia]]'', and four extinct genera. The living genus lives in the river basins of [[South America]], but the family formerly had a wider presence across the [[Atlantic Ocean]].

Iniidae are highly morphologically different from [[Oceanic dolphin|marine dolphins]] due to adaptations suited to their freshwater river habitat.<ref name=Hamilton2001/> They display high amounts of [[sexual dimorphism]] through color and size.<ref name=Martin2006>{{cite journal |author1=Martin, A.R. |author2=Silva, V.M. |year=2006 |title=Sexual dimorphism and body scarring in the boto (Amazon river dolphin) ''Inia geoffrensis'' |journal=Marine Mammal Science |volume=22 |issue=1 |pages=25–33 |doi=10.1111/j.1748-7692.2006.00003.x|bibcode=2006MMamS..22...25M }}</ref> Seasonal movement between flooded plains and rivers is common, due to the variation of seasonal rain.<ref name=Rice1998>{{cite book |author=Rice, Dale W. |year=1998 |title=Marine Mammals of the World: Systematics and distribution |series=Society for Marine Mammalogy Special Publication |place=Lawrence, KS |publisher=Society for Marine Mammalogy |volume=4 |pages=1–231 |isbn=978-1-891276-03-3}} {{isbn|1891276034}}</ref> There has been little research done on the family, in particular the species aside from the [[Amazon river dolphin]].<ref name=Martin2006/>

==Evolution== The South American river basins were flooded by marine waters during the mid-[[Miocene]] era, creating a new brackish habitat that allowed marine mammals to move into them. Marine animals that could tolerate the osmotic difference in the salt and freshwater systems permeated these habitats and adapted. Over time, the sea level began to recede, trapping the mammals within the continent in the river basins.<ref name="Hamilton2001">{{cite journal |author1=Hamilton, Healy |display-authors=etal |year=2001 |title=Evolution of river dolphins |journal=Proceedings of the Royal Society of London B: Biological Sciences |volume=268 |issue=1466 |pages=549–556|doi=10.1098/rspb.2000.1385 |pmid=11296868 |pmc=1088639 }}</ref>

== Morphology == Because their cervical vertebra are movable, the necks of Iniidae are flexible; this makes them unlike most whales, dolphins, and porpoises, which have fused neck vertebrae, rigidly aiming their heads forward.<ref name=Gomez2011/> The Iniidae have other morphology common to species adapted to freshwater river habitats,<ref name=Gutstien2011>{{cite journal |last1=Gutstien |first1=Carolina |year=2014 |title=The antiquity of riverine adaptations in Iniidae (Cetacea, Odontoceti) documented by a humerus from the Late Miocene of the Ituzaingo Formation, Argentina |journal=The Anatomical Record |volume=297 |issue=6 |pages=1096–1102 |doi=10.1002/ar.22901 |doi-access=free |pmid=24585575 |s2cid=42361824}}</ref> including highly reduced or absent dorsal fins, which helps them avoid entanglement in vegetation from the flooded terrestrial plains, and large, wide, paddle-like pectoral fins that allow maneuverability in confined areas cramped by vegetation.<ref name=Gomez2011>{{cite journal |author=Gomez-Salazar, C. |year=2011 |title=Photo-identification: A reliable and noninvasive tool for studying pink river dolphins (Inia geoffrensis) |journal=Aquatic Mammals |volume=37 |issue=4 |pages=472–485 |doi=10.1578/am.37.4.2011.472|bibcode=2011AqMam..37..472G }}</ref> Other adaptations including a long [[Rostrum (anatomy)|rostrum]], skull, and jaw, and reduced orbits.<ref>{{cite journal |author1=Pyenson, N.D. |author1-link=Nicholas Pyenson |author2=Vélez-Juarbe, J. |author3=Gutstein, C.S. |author4=Little, H. |author5=Vigil, D. |author6=O'Dea, A. |date=1 September 2015 |title=''Isthminia panamensis'', a new fossil Inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of 'river dolphins' in the Americas |journal=PeerJ |volume=3 |article-number=e1227 |publisher=PeerJ Inc |pmid=26355720 |pmc=4562255 |doi=10.7717/peerj.1227 |doi-access=free }}</ref>

Iniidae share other characteristics with their marine [[odontocete|toothed whale]] relatives. Their stomachs include a fore-stomach, a single-chambered main stomach, and a pyloric stomach with connecting channels. They also share similarities with their marine ancestors in terms of lung shape, the position of the diaphragm, the position of the blowhole toward the back of the head, and the structure of the tympanic bulla. Iniidae have lost their fur and lack true vocal cords.<ref name=Kaiya-1982>{{cite journal |author=Kaiya, Zhou |year=1982 |title=Classification and phylogeny of the superfamily Platanistoidea, with notes on evidence of the monophyly of the Cetacea |journal=Sci. Rep. Whale Res. Inst. |volume=34 |pages=93–108}}</ref>

Iniidae dolphins develop multiple sets of teeth, including small conical teeth that differ slightly in the front of the mouth. The teeth extend lingually in the back, and in the front have a small depression on each side. These mammals are carnivorous, finding prey via echolocation.{{citation needed|date=November 2017}}

==Speciation== There is scientific debate on the number of species within the genus ''Inia.'' The main issue is whether there are two or three (or even four) species, or whether any of them should be considered sub-species. According to some researchers, ''Inia geoffrensis'', ''Inia humboldtiana'', and ''Inia boliviensis'' are three separate species, while many consider ''I. geoffrensis'' and ''I. boliviensis'' to be the only two.<ref name="Gravena2014">{{cite journal |author1=Gravena, Waleska |display-authors=etal |year=2014 |title=Looking to the past and the future: Were the Madeira River rapids a geographical barrier to the boto (Cetacea: Iniidae)? |journal=Conservation Genetics |volume=15 |issue=3 |pages=619–629}}</ref><ref>{{cite journal |author1=Ruiz-García, M. |author2=Banguera, E. |author3=Cardenas, H. |year=2006 |title=Morphological analysis of three Inia (Cetacea: Iniidae) populations from Colombia and Bolivia |journal=Acta Theriologica |volume=51 |issue=4 |pages=411–426 |doi=10.1007/bf03195188|s2cid=22868836 }}</ref><ref name="Rice1998" /> Martin (2004) found evidence that genetic exchange occurs at multiple sites on the Amazon, even places hundreds of kilometres apart.<ref>{{Cite journal |last=Martin |first=A. R. |last2=da Silva |first2=V. M. F. |date=2004 |title=River dolphins and flooded forest: seasonal habitat use and sexual segregation of botos ( Inia geoffrensis ) in an extreme cetacean environment |url= |journal=Journal of Zoology |language=en |volume=263 |issue=3 |pages=295–305 |doi=10.1017/S095283690400528X |issn=0952-8369}}</ref>

==Taxonomy== The family was described by [[John Edward Gray]] in 1846.<ref name=TPBDB>{{cite web |title=''Inia'' taxon description |website=The Paleobiology Database |url=https://paleobiodb.org/classic/checkTaxonInfo?taxon_no=53142 |url-status=live |access-date=2022-09-21 |archive-date=2012-10-12 |archive-url=https://web.archive.org/web/20121012212849/http://paleodb.org/cgi-bin/bridge.pl?action=checkTaxonInfo&taxon_no=53142&is_real_user=1 }}</ref>

Current classifications include a single living genus, ''Inia'', with one to four species and several subspecies.<ref name=Hrbek2014> {{cite journal | last1 = Hrbek | first1 = Tomas | last2 = da Silva | first2 = Vera Maria Ferreira | last3 = Dutra | first3 = Nicole | last4 = Gravena | first4 = Waleska | last5 = Martin | first5 = Anthony R. | last6 = Farias | first6 = Izeni Pires | date = 2014-01-22 | title = A new species of river dolphin from Brazil or: How little do we know our biodiversity? | journal = [[PLOS ONE]] | volume = 9 | issue = 1 | article-number = e83623 | pmid = 24465386 | pmc = 3898917 | bibcode = 2014PLoSO...983623H | doi = 10.1371/journal.pone.0083623 | doi-access = free  }} </ref><ref>{{unbulleted list citebundle| {{cite mdd |genus=Inia |species=boliviensis |id=1006455 |access-date=2026-02-03 }}|{{cite mdd |genus=Inia |species=humboldtiana |id=1006502 |access-date=2026-02-03}}|{{cite mdd |id=1006454 |genus=Inia |species=araguaiaensis |access-date=2026-02-03}}|{{cite mdd |genus=Inia |species=geoffrensis |id=1006456 |access-date=2026-02-03}}}} </ref> The family also includes three extinct genera described from fossils found in South America, [[Florida]], [[Libya]], and [[Italy]].<ref name=TPBDB/>

*Superfamily [[Inioidea]] **Family Iniidae ***Genus †''[[Goniodelphis]]'' **** ''G. hudsoni'' ***Genus ''[[Inia]]'' **** ''Inia araguaiaensis'' - [[Araguaian river dolphin]] **** ''Inia boliviensis'' - [[Bolivian river dolphin]] **** ''Inia geoffrensis'' - [[Amazon river dolphin]] ****''Inia humboldtiana'' - [[Orinoco river dolphin]] ***Genus †''[[Isthminia]]'' ****†''[[Isthminia panamensis]]'' ***Genus †''[[Meherrinia]]'' ***Genus †''[[Ischyrorhynchus]]'' (syn. ''Anisodelphis'') **** ''I. vanbenedeni'' (syn. ''Anisodelphis brevirostratus'') ***Genus †''[[Saurocetes]]'' (syn. ''Saurodelphis'', ''Pontoplanodes'') **** ''S. argentinus'' (syn. ''Pontoplanodes obliquus'') **** ''S. gigas''

==References== {{reflist|25em}}

[[Category:Iniidae| ]] [[Category:Mammals of South America]] [[Category:Mammals of Brazil]] [[Category:Mammals of Peru]] [[Category:Mammal families]] [[Category:Taxa named by John Edward Gray]]