Iniidae is a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of river dolphins containing one living genus, '' Inia'', and four extinct genera. The extant genus inhabits the river basins of

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

, but the family formerly had a wider presence across the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

. Iniidae are highly morphologically different from marine dolphins by way of adaptations suited to their freshwater riverine habitat. They also display a high amount of

sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...

in the form of color and size. Seasonal movement between flooded plains and rivers is common, due to the variation of seasonal rain. There has been little research done on the family, in particular the species aside from the Amazon river dolphin.

Evolution

The South American river basins were flooded by marine waters, 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.

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. The Iniidae have other morphology common to species adapted to freshwater riverine habitats; 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. Other riverine adaptations including a long rostrum, skull and jaw and reduced orbits. 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. 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, 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 * ''Inia geoffrensis'' * ''Inia humboldtiana'' * ''Inia boliviensis'' are three separate species, while many consider ''I. geoffrensis'' and ''I. boliviensis'' to be the only two. Martin in 2004 found supporting evidence that genetic exchange occurs between multiple sites on the Amazon, even places hundreds of kilometres apart.

Taxonomy

The family was described by

John Edward Gray John Edward Gray (12 February 1800 – 7 March 1875) was a British zoologist. He was the elder brother of zoologist George Robert Gray and son of the pharmacologist and botanist Samuel Frederick Gray (1766–1828). The same is used for a z ...

in 1846. Current classifications include a single living genus, ''Inia'', with one to four species and several subspecies. The family also includes three extinct genera described from fossils found in

Florida Florida ( ; ) is a U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders the Gulf of Mexico to the west, Alabama to the northwest, Georgia (U.S. state), Georgia to the north, the Atlantic ...

Libya Libya, officially the State of Libya, is a country in the Maghreb region of North Africa. It borders the Mediterranean Sea to the north, Egypt to Egypt–Libya border, the east, Sudan to Libya–Sudan border, the southeast, Chad to Chad–L ...

, and

Italy Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...

. *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

External links

{{Taxonbar, from=Q54873 Mammals of South America Mammals of Brazil Mammals of Peru Mammal families Taxa named by John Edward Gray