Iniidae

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Iniidae
Temporal range: Miocene-Holocene
Inia.jpg
An Amazon river dolphin at Duisburg Zoo holding an Armored catfish in the mouth.
Amazon river dolphin size.svg
Size compared to an average human
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Superfamily: Inioidea
Family: Iniidae
Gray, 1846
Genera

Inia

Iniidae is a family of river dolphins containing one living genus, Inia , and four extinct genera. The extant genus inhabits the river basins of South America, but the family formerly had a wider presence across the Atlantic Ocean.

Contents

Iniidae are highly morphologically different from marine dolphins by way of adaptations suited to their freshwater riverine habitat. [1] They also display a high amount of sexual dimorphism in the form of color and size. [2] Seasonal movement between flooded plains and rivers is common, due to the variation of seasonal rain. [3] There has been little research done on the family, in particular the species aside from the Amazon river dolphin. [2]

Evolution

The South American river basins were flooded by marine waters,[ when? ] creating a new brackish habitat that allowed marine mammals to move into them. During the Miocene era, the sea level began to recede, trapping the mammals within the continent. [1]

Morphology

Their necks are flexible, since their cervical vertebra are movable; this is remarkable since nearly all cetaceans' neck vertebra are fused, which rigidly aims most other cetaceans' heads forward. [4] The Iniidae have other morphology common to species adapted to freshwater riverine habitats; [5] which include highly reduced or absent dorsal fins, so they do not become entangled in vegetation from the flooded terrestrial plains; and large, wide, paddle-like pectoral fins that allow maneuverability in confined areas cramped by vegetation. [4] Other riverine adaptations including a long rostrum, skull and jaw and reduced orbits. [6]

Iniidae share many other characteristics in common with their marine odontocete relatives: Their stomachs include a fore-stomach, singled chambered main stomach, and a pyloric stomach with connecting channels. Like most other cetaceans Iniidae have lost their fur and lack true vocal cords. [7] They share the similar structure of the tympanic bulla and lung shape, the position of their diaphragm and the position of the blowhole to the back of the head with their marine ancestors.

The dentition of Iniidae dolphins is heterodont,[ citation needed ] having conical, small teeth that differ slightly in the front of the mouth. The teeth extend lingually in the back and in the front they have a small depression on the side of each. These mammals are carnivorous, finding prey by using echolocation.

Speciation

There is scientific debate on the number of species within the genus Inia: The main issue is whether there are two or three species, or whether those can be considered sub-species. According to some researchers

are three separate species, while many consider I. geoffrensis and I. boliviensis to be the only two. [8] [9] [3] Martin in 2004 found supporting evidence that genetic exchange occurs between multiple sites on the Amazon, even places hundreds of kilometres apart.[ citation needed ]

Taxonomy

The family was described by John Edward Gray in 1846. [10]

Current classifications include a single living genus, Inia, with one to four species and several subspecies. [11] [12] The family also includes three extinct genera described from fossils found in South America, Florida, Libya, and Italy. [10]

Related Research Articles

<span class="mw-page-title-main">Cetacea</span> Infraorder of mammals

Cetacea is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel themselves through the water with powerful up-and-down movement of their tail which ends in a paddle-like fluke, using their flipper-shaped forelimbs to maneuver.

<span class="mw-page-title-main">Artiodactyl</span> Order of mammals

Artiodactyls are mammals belonging to the order Artiodactyla. Typically, they are ungulates which bear weight equally on two of their five toes: the third and fourth, often in the form of a hoof. The other three toes are either present, absent, vestigial, or pointing posteriorly. By contrast, most perissodactyls bear weight on an odd number of the five toes. Another difference between the two is that many artiodactyls digest plant cellulose in one or more stomach chambers rather than in their intestine as perissodactyls do. The advent of molecular biology, along with new fossil discoveries, found that cetaceans fall within this taxonomic branch, being most closely related to hippopotamuses. Some modern taxonomists thus apply the name Cetartiodactyla to this group, while others opt to include cetaceans within the existing name of Artiodactyla. Some researchers use "even-toed ungulates" to exclude cetaceans and only include terrestrial artiodactyls, making the term paraphyletic in nature.

<span class="mw-page-title-main">Amazon river dolphin</span> Species of toothed whale

The Amazon river dolphin, also known as the boto, bufeo or pink river dolphin, is a species of toothed whale endemic to South America and is classified in the family Iniidae. Three subspecies are currently recognized: I. g. geoffrensis, I. g. boliviensis and I. g. humboldtiana while position of Araguaian river dolphin within the clade is still unclear. The three subspecies are distributed in the Amazon basin, the upper Madeira River in Bolivia, and the Orinoco basin, respectively.

<span class="mw-page-title-main">River dolphin</span> Superfamily of dolphins

River dolphins are a polyphyletic group of fully aquatic mammals that reside exclusively in freshwater or brackish water. They are an informal grouping of dolphins, which itself is a paraphyletic group within the infraorder Cetacea. Extant river dolphins are placed in two superfamilies, Platanistoidea and Inioidea. They comprise the families Platanistidae, the recently extinct Lipotidae, Iniidae and Pontoporiidae. There are five extant species of river dolphins. River dolphins, alongside other cetaceans, belong to the clade Artiodactyla, with even-toed ungulates, and their closest living relatives the hippopotamuses, from which they diverged about 40 million years ago. Specific types of dolphins can be pink.

<span class="mw-page-title-main">South Asian river dolphin</span> Genus of freshwater dolphin

South Asian river dolphins are toothed whales in the genus Platanista, which inhabit the waterways of the Indian subcontinent. They were historically considered to be one species with the Ganges river dolphin and the Indus river dolphin being subspecies. Genetic and morphological evidence led to their being described as separate species in 2021. The Ganges and Indus river dolphins are estimated to have diverged 550,000 years ago. They are the only living members of the family Platanistidae and the superfamily Platanistoidea. Fossils of ancient relatives date to the late Oligocene.

<span class="mw-page-title-main">Hector's beaked whale</span> Species of mammal

Hector's beaked whale, is a small mesoplodont living in the Southern Hemisphere. This whale is named after Sir James Hector, a founder of the colonial museum in Wellington, New Zealand. The species has rarely been seen in the wild.

<span class="mw-page-title-main">Tucuxi</span> Species of mammal

The tucuxi, alternatively known in Peru bufeo gris or bufeo negro, is a species of freshwater dolphin found in the rivers of the Amazon basin. The word tucuxi is derived from the Tupi language word tuchuchi-ana, and has now been adopted as the species' common name. Despite being found in geographic locations similar to those of 'true' river dolphins such as the boto, the tucuxi is not closely related to them genetically. Instead, it is classed in the oceanic dolphin family (Delphinidae).

<i>Inia</i> Genus of dolphins

Inia is a genus of river dolphins from South America containing one to four species.

<i>Lagenorhynchus</i> Genus of mammals

Lagenorhynchus is a genus of oceanic dolphins in the infraorder Cetacea, presently containing six extant species. However, there is consistent molecular evidence that the genus is polyphyletic and several of the species are likely to be moved to other genera. In addition, the extinct species Lagenorhynchus harmatuki is also classified in this genus.

<span class="mw-page-title-main">Aquatic mammal</span> Mammal that dwells partly or entirely in bodies of water

Aquatic and semiaquatic mammals are a diverse group of mammals that dwell partly or entirely in bodies of water. They include the various marine mammals who dwell in oceans, as well as various freshwater species, such as the European otter. They are not a taxon and are not unified by any distinct biological grouping, but rather their dependence on and integral relation to aquatic ecosystems. The level of dependence on aquatic life varies greatly among species. Among freshwater taxa, the Amazonian manatee and river dolphins are completely aquatic and fully dependent on aquatic ecosystems. Semiaquatic freshwater taxa include the Baikal seal, which feeds underwater but rests, molts, and breeds on land; and the capybara and hippopotamus which are able to venture in and out of water in search of food.

<span class="mw-page-title-main">Boto</span>

Boto is a Portuguese name given to several types of dolphins and river dolphins native to the Amazon and the Orinoco River tributaries. A few botos exist exclusively in fresh water, and these are often considered primitive dolphins.

<span class="mw-page-title-main">Kentriodontidae</span> Extinct family of dolphins

Kentriodontidae is an extinct family of odontocete whales related to modern dolphins. The Kentriodontidae lived from the Oligocene to the Pliocene before going extinct.

<span class="mw-page-title-main">Bolivian river dolphin</span> Subspecies of Amazon river dolphin

The Bolivian river dolphin is a species of the genus Inia.

<span class="mw-page-title-main">Artiofabula</span> Clade of mammals comprising pigs, cows, hippos, and whales, among others

Artiofabula is a clade made up of the Suina and the Cetruminantia. The clade was found in molecular phylogenetic analyses and contradicted traditional relationships based on morphological analyses.

Meherrinia is an extinct genus of inioid river dolphin from the Meherrin River, North Carolina, in the United States. First described in 2012, the dolphin is, in most respects, intermediate in form between the living Amazon river dolphin and the La Plata dolphin, although it is probably more closely related to the former. However, the fossil was discovered in what are believed to be marine deposits, dating from the late Miocene, whereas the Amazon river dolphin is an exclusively freshwater species. Meherrinia therefore was, as of 2012, the only known marine genus of the family Iniidae, although others have been discovered since. Only one species is known.

<span class="mw-page-title-main">Araguaian river dolphin</span> Species of mammal

The Araguaian river dolphin or Araguaian boto is a South American river dolphin population native to the Araguaia–Tocantins basin of Brazil.

<i>Isthminia</i> Extinct genus of mammals

Isthminia is a genus of medium-sized river dolphin cetaceans that lived during the Late Miocene epoch in what is now the coasts of Panama, about 6.1 million to 5.8 million years ago. The type species is I. panamensis, known from the littoral Chagres Formation.

Saurocetes is an extinct genus of probable iniid river dolphins from South America. Two species have been described: S. argentinus and S. gigas. It has been suggested that Saurocetes is a synonym of the possible platanistid Ischyrorhynchus.

References

  1. 1 2 Hamilton, Healy; et al. (2001). "Evolution of river dolphins". Proceedings of the Royal Society of London B: Biological Sciences. 268 (1466): 549–556. doi:10.1098/rspb.2000.1385. PMC   1088639 . PMID   11296868.
  2. 1 2 Martin, A.R.; Silva, V.M. (2006). "Sexual dimorphism and body scarring in the boto (Amazon river dolphin) Inia geoffrensis". Marine Mammal Science. 22 (1): 25–33. doi:10.1111/j.1748-7692.2006.00003.x.
  3. 1 2 Rice, Dale W. (1998). Marine Mammals of the World: Systematics and distribution. Society for Marine Mammalogy Special Publication. Vol. 4. Lawrence, KS: Society for Marine Mammalogy. pp. 1–231. ISBN   978-189127603-3. ISBN   1891276034
  4. 1 2 Gomez-Salazar, C. (2011). "Photo-identification: A reliable and noninvasive tool for studying pink river dolphins (Inia geoffrensis)". Aquatic Mammals. 37 (4): 472–485. doi:10.1578/am.37.4.2011.472.
  5. Gutstien, Carolina (2014). "The antiquity of riverine adaptations in Iniidae (Cetacea, Odontoceti) documented by a humerus from the Late Miocene of the Ituzaingo Formation, Argentina". The Anatomical Record. 297 (6): 1096–1102. doi: 10.1002/ar.22901 . PMID   24585575. S2CID   42361824.
  6. Pyenson, N.D.; Vélez-Juarbe, J.; Gutstein, C.S.; Little, H.; Vigil, D.; O’Dea, A. (1 September 2015). "Isthminia panamensis, a new fossil Inioid (Mammalia, Cetacea) from the Chagres Formation of Panama and the evolution of 'river dolphins' in the Americas". PeerJ. PeerJ Inc. 3: e1227. doi: 10.7717/peerj.1227 . PMC   4562255 . PMID   26355720.
  7. Kaiya, Zhou (1982). "Classification and phylogeny of the superfamily Platanistoidea, with notes on evidence of the monophyly of the Cetacea". Sci. Rep. Whale Res. Inst. 34: 93–108.
  8. Gravena, Waleska; et al. (2014). "Looking to the past and the future: Were the Madeira River rapids a geographical barrier to the boto (Cetacea: Iniidae)?". Conservation Genetics. 15 (3): 619–629.
  9. Ruiz-García, M.; Banguera, E.; Cardenas, H. (2006). "Morphological analysis of three Inia (Cetacea: Iniidae) populations from Colombia and Bolivia". Acta Theriologica. 51 (4): 411–426. doi:10.1007/bf03195188. S2CID   22868836.
  10. 1 2 "Inia taxon description". The Paleobiology Database. Archived from the original on 2012-10-12. Retrieved 2022-09-21.
  11. Hrbek, Tomas; da Silva, Vera Maria Ferreira; Dutra, Nicole; Gravena, Waleska; Martin, Anthony R.; Farias, Izeni Pires (2014-01-22). "A new species of river dolphin from Brazil or: How little do we know our biodiversity?". PLOS ONE . 9 (1): e83623. Bibcode:2014PLoSO...983623H. doi: 10.1371/journal.pone.0083623 . PMC   3898917 . PMID   24465386.
  12. "Inia". ASM Mammal Diversity Database. American Society of Mammalogists . Retrieved 2021-09-05.