South Asian river dolphin

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South Asian river dolphin
Temporal range: 0.012–0  Ma
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Quaternary – recent [1]
Ganges River Dolphin cropped.jpg
Ganges river dolphin breaking the surface
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Infraorder: Cetacea
Family: Platanistidae
Genus: Platanista
Wagler, 1830
Type species
Delphinus gangeticus [2]
Lebeck, 1801
Species

Platanista gangetica
Platanista minor

SouthAsianRiverDolphin distribution2019.png
Current ranges of the Indus river dolphin and Ganges river 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 (P. gangetica) with the Ganges river dolphin and the Indus river dolphin being subspecies (P. g. gangetica and P. g. minor respectively). 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.

Contents

South Asian river dolphins are small but stocky cetaceans with long snouts or rostra, broad flippers, and small dorsal fins. They have several unusual features. Living in murky river waters, they have eyes that are tiny and lensless; the dolphins rely instead on echolocation for navigation. The skull has large crests over the melon, which help direct their echolocation signals. These dolphins prey mainly on fish and shrimp and hunt them throughout the water column. They are active through the day and are sighted in small groups. Both species are listed as endangered by the IUCN Red List of mammals. Major threats include dams, barrages, fishing nets, and both chemical and acoustic pollution.

Taxonomy

South Asian river dolphins were traditionally considered to be one species, Platanista gangetica, with the Ganges and Indus River populations being subspecies (P. g. gangetica and P. g. minor, respectively). Heinrich Julius Lebeck named the Ganges river dolphin Delphinus gangeticus in 1801, while Johann Georg Wagler coined the genus name Platanista in 1830, [3] a Latin word derived from the Greek "platanistēs", which may be related to the Greek words platē ("oar") or platē ("flat, broad"). [4] This name was first given to the Ganges dolphin by Pliny the Elder in Naturalis Historia back in 77 CE. In 1853, Richard Owen described a specimen from the Indus and considered it to be the same species as the Ganges river dolphin, but a smaller form. [3]

Based on differences in skull and vertebrae structure, blood proteins, and lipids, scientists declared them to be separate species in the 1970s. [5] [6] The results of these studies were criticized for their small sample sizes and the absence of statistical analyses; by the late 1990s, the two populations were again considered to be two subspecies of a single species. [7] [6] A 2014 mitochondrial DNA study found insufficient differences to support their classification as separate species. [6] However, a 2021 study reanalyzed the two populations and found significant genetic divergence and major differences in skull structure; this led to the conclusion that the two were indeed distinct species. [3]

Evolution

South Asian river dolphins are the only surviving members of the family Platanistidae and the superfamily Platanistoidea. [8] They are not closely related to other river dolphins of the families Lipotidae, Pontoporiidae, and Iniidae, which all independently adapted to freshwater habitats. [9] The following cladogram is based on Gatesy and colleagues (2012) and McGowen and colleagues (2020); and shows the relationship of South Asian river dolphins to other living toothed whale families: [10] [11]

  Toothed whales  

  Sperm whales (Physeteridae) Physeter macrocephalus NOAA.jpg

  Dwarf sperm whales (Kogiidae) Kogia sima (transparent background).png

 South Asian river dolphins (Platanistidae) Ganges.png

  Beaked whales (Ziphiidae) Ziphius cavirostris NOAA.jpg

 South American river dolphins 
  Delphinoidea  

  Oceanic dolphins (Delphinidae) Orcinus orca NOAA 2.jpg

  Porpoises  (Phocoenidae) Vaquita swimming through the void. (Phocoena Sinus).png

  Belugas, narwhals (Monodontidae) Delphinapterus leucas NOAA.jpg

Several fossil species have been classified under Platanistoidea, the earliest of which date back to the late Oligocene (c. 25 million years ago). The number of species peaked around the early Miocene (c. 19 million years ago) and declined afterward. Examples of ancient platanistids include the genera Otekaikea and Waipatia and the species Awamokoa tokarahi of late Oligocene New Zealand, the family Allodelphinidae of early Miocene North Pacific, and Notocetus vanbenedeni and Aondelphis talen of early Miocene Patagonia. Platanistidae fossils have been found in Miocene deposits in Europe and North America. Fossil Platanistoidea showed a diversity of cochlea shapes, though Platanista was unusual in that it developed flatter spirals with larger gaps between them. [8]

During the middle Miocene, the ancestor of Platanista entered the Indo-Gangetic Plain, then covered by inland seas, and remained there when sea levels dropped in the late Neogene and its environment converted to freshwater. [9] River dolphins likely traveled from the Ganges River basin to the Indus via stream capture within the last five million years. The split between the two species is estimated to have occurred around 550,000 years ago based on mitochondrial DNA. [12]

Description

A-Platanista-gangetica-showing-the-body-shape-and-especially-the-head-with-a-long-beak.png
Indus River dolphin skull cast.jpg
Full body (top) and skull of Indus river dolphin

South Asian river dolphins are stocky with broad, squared-off pectoral fins; elongated, slender rostrums (snouts); and tiny triangular dorsal fins. Their neck joints give them great flexibility. [3] [13] [14] Unusual among cetaceans, the blowhole is slit-shaped. [14] The finger bones can also be seen through the flippers. [13] South Asian river dolphins possess some features that are "primitive" for a cetacean, such as a cecum connected to the gut and air sacs near the blowhole. The testes of the males are located closer to the underside than in marine dolphins and descend more. [15] Their skin ranges from grey to greyish-brown in colour, though the rostrum and surrounding areas may have some pinkish colouration. The Indus species tends to be more brownish. [3]

In one study sampling 46 Ganges river dolphins, the maximum length and weight recorded were 267 cm (8.76 ft) and 108 kg (238 lb). For the Indus species, the maximum length and weight were 241 cm (7.91 ft) and 120 kg (260 lb) (80 individuals sampled). Female Ganges dolphins are generally longer than Indus dolphins of both sexes, while male Ganges dolphins are shorter than Indus dolphins of both sexes. Indus dolphins tend to be proportionally heavier than Ganges dolphins, independent of sex. [3]

South Asian river dolphin skulls have unusual features. The maxilla (fixed upper jawbone) has pneumatic extensions or "crests" on each side which curve around the melon and protrude forward over the rostrum. These likely help them focus their echolocation signals in their riverine environment. [16] The Ganges species also has a protrusion near the frontal suture, which distinguishes it from the Indus species. [3] The teeth of South Asian river dolphins are curved and longer in the front, where they remain exposed when the jaws are closed. [14] Indus dolphins have more teeth than Ganges dolphins, averaging 33.2 teeth in the upper jaw and the 32.9 in the lower jaw, as compared to 28.4 in the upper jaw and 29.4 in the lower. [3]

Living in murky waters, South Asian river dolphins are nearly blind, their tiny eyes having flattened corneas and no lens. The retina—which connects to a reduced optic nerve—does not form images but instead merely discerns light. The animal relies on a sphincter-like muscle around the eye to control access to the retina and prevent light scattering, similar to a pinhole. [17] The ears are adapted to hearing low frequencies, having a short, flattened cochlea with widely spaced spirals. [8]

Distribution and habitat

Ganges river dolphin in the Sundarbans, Bangladesh South Asian river dolphin(c) Md Sharif Hossain Sourav.jpg
Ganges river dolphin in the Sundarbans, Bangladesh

South Asian river dolphins inhabit the northern waterways of the Indian subcontinent. Ganges river dolphins live in the Ganges, Brahmaputra, Meghna, Karnaphuli, and Sangu rivers and their tributaries. Their range extends from the Himalayan foothills to the Ganges Delta, across the countries of Nepal, India and Bangladesh. [3] [14] It is unknown if they are present in Bhutan. [18] Outflows of freshwater into the Bay of Bengal have allowed them to swim along the coast, and there is at least one record of an individual entering the Budhabalanga River, around 300 km (190 mi) southwest of the Ganges Delta. [19] This species has maintained much of its range since the 19th century but has disappeared from some northern and western rivers and waterways. [3]

The Indus river dolphin mainly lives in the Indus River of Pakistan, with three subpopulations between the Chashma, Taunsa, Guddu, and Sukkur barrages. Two other populations exist south of Sukkur and in the Beas River of India. [3] [20] In the 19th century, this species was reported to have occurred throughout the Indus River system, from the Indus River Delta north to Kalabagh just south of the Himalayas, including all the main tributaries. [3] The Indus river dolphin is reported to have disappeared between the Jinnah and Chashma barrages after 2001. [20]

South Asian river dolphins inhabit major river channels during the dry season and travel to smaller tributaries for the monsoon. They are most commonly found in stream pools, meanders, and confluences, and around river islands and shoals, which produce relatively stable waters. [19] They can be found in pools over 30 m (98 ft) deep, but usually dwell in shallower water. [14]

Behaviour and life history

South Asian river dolphins appear to be active throughout the day. Living in flowing waters, they swim almost constantly with only brief periods of sleep, which add up to seven hours per day. [21] They swim on their sides when in shallow water. [22] River dolphins generally surface with the rostrum, head, and dorsal fin breaking the water and rarely breach or raise the tail fluke, though surface activity can vary based on age, distance from shore and time of day. Diving may last as long as eight minutes among adults and subadults; dives of newborns and juveniles are not as long. [23]

Indus river dolphins leaping B-Platanista-gangetica-in-natural-habitat.png
Indus river dolphins leaping

River dolphins are typically seen alone or in groups of up to 10 individuals, though enough natural resources may attract up to 30 dolphins. Individuals do not appear to have strong social bonds, outside of mothers and calves. [14] Living in shallow river environments with acoustic obstacles, these dolphins echolocate using repetitive clicks spaced 10 to 100 milliseconds apart. [24] [25] Their clicks are about one octave below those of oceanic toothed whales of comparable size, meaning that they provide less information about the location of an object, but the dolphins' maxillary crests likely compensate by providing greater directional sensitivity. [16] Vocalisations used for communication include bursts and twitterings. [26]

River dolphins feed mainly on fish and shrimp. In one meta study, around 46% of prey items were found to be bottom-dwelling species, while 31% were near the surface, and 23% occupied the middle of the column. The most frequently taken prey are bagrid catfish, barbs, glass perches, spiny eels, gobies, and prawns. When hunting at the surface, dolphins listen for the movements of schooling fish which are then herded with spins, side-swimming, and lobtailing. Echolocation signals are not frequently used at the surface, since many fish at this level can hear ultrasound. At the mid-surface level, the dolphins use more echolocation clicks to find prey hidden in clutter and vegetation as far as 20 m (66 ft) away. They flush out bottom-dwelling prey by digging around. [22]

Little is known about reproduction in these river dolphins. [14] Courtship and mating behaviour for the Ganges species has been documented from March to May, when the water level is lower, and involves multiple males chasing one female and ends with one of the males earning the right to mate. [15] Calves are born around a year later. [27] Births in the Ganges river dolphin appear to be most frequent between December and January and between March and May. For Indus river dolphins, newborns are most commonly seen between April and May. [14] Indus river dolphins calves are around 70 cm (28 in) long at birth and may nurse for up to a year. They eat their first solid food within a couple months. South Asian river dolphins reach sexual maturity at around ten years, though males may not reach their adult size until 20 years. [28] Growth layers in the teeth suggest South Asian river dolphins can live up to 30 years. [29]

Conservation

Man holding Ganges river dolphin in Bhagalpur Ganges-river-dolphins.jpg
Man holding Ganges river dolphin in Bhagalpur

As of 2022, the IUCN Red List of mammals lists both South Asian river dolphins as endangered. [18] [30] Two assessments in 2014 and 2015 estimated populations of 3,500 for the Ganges river dolphin and 1,500 for the Indus river dolphin. [19] [31] The Ganges species appears to be decreasing, while the Indus species may be increasing. [18] [30] The habitat of these river dolphins intersects with some of the most densely populated areas, leading to intense competition for water and resources. [19] [31] [32]

The creation of dams and barrages in the Indus River system have heavily fragmented the range of the Indus river dolphin, leading to a population decline of 80% since the 19th century. [31] Around 50 such structures have been built in the historical range of the Ganges species. [19] Fragmentation of populations makes these dolphins more vulnerable to inbreeding. [32] The heavy extraction of water in these dense populations also puts the dolphins at risk. [19]

River dolphins accumulate high amounts of persistent organic pollutants, pesticides, and heavy metals in their system due to being at the top of their riverine food web. [19] [31] Hence, they are seen as bioindicators for the health of river systems. [19] Fishermen compete with these animals for fish of certain sizes. [32] Dolphins captured in fishing nets are usually accidental, but dolphin oil is sought after as a fish lure, and thus fishermen may be motivated to kill caught dolphins. [19] Being nearly blind and relying on echolocation for navigation, river dolphins are also negatively affected by noise pollution from boats. [33]

South Asian river dolphins are protected by law in all the states they inhabit. They can be found in numerous protected areas, [18] [30] including ones established specifically for them, such as the Indus Dolphin Reserve in Pakistan and the Vikramshila Gangetic Dolphin Sanctuary in India. [19] [31] International trade is prohibited by the listing of the South Asian river dolphins on Appendix I of the Convention on International Trade in Endangered Species. [34] The Ganges and Indus river dolphins are considered to be the national aquatic animals of India and Pakistan respectively. [35] [36]

See also

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">Animal echolocation</span> Method used by several animal species to determine location using sound

Echolocation, also called bio sonar, is a biological active sonar used by several animal groups, both in the air and underwater. Echolocating animals emit calls and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects. Echolocation is used for navigation, foraging, and hunting prey.

<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">Iniidae</span> Family of dolphins

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.

<span class="mw-page-title-main">Platanistidae</span> Family of dolphins

Platanistidae is a family of river dolphins containing the extant Ganges river dolphin and Indus river dolphin but also extinct relatives from freshwater and marine deposits in the Neogene.

<span class="mw-page-title-main">Physeteroidea</span> Superfamily of toothed whales

Physeteroidea is a superfamily that includes three extant species of whales: the sperm whale, in the genus Physeter, and the pygmy sperm whale and dwarf sperm whale, in the genus Kogia. In the past, these genera have sometimes been united in a single family, the Physeteridae, with the two Kogia species in the subfamily Kogiinae; however, recent practice is to allocate the genus Kogia to its own family, the Kogiidae, leaving the Physeteridae as a monotypic family, although additional fossil representatives of both families are known.

<span class="mw-page-title-main">Kogiidae</span> Family of mammals

Kogiidae is a family comprising at least two extant species of Cetacea, the pygmy and dwarf sperm whales. As their common names suggest, they somewhat resemble sperm whales, with squared heads and small lower jaws, but are much smaller in size, with much shorter skulls and more notable dorsal fins than sperm whales. Kogiids are also characterized by a "false gill slit" behind their eyes.

<span class="mw-page-title-main">Toothed whale</span> Parvorder of cetaceans

The toothed whales are a parvorder of cetaceans that includes dolphins, porpoises, and all other whales possessing teeth, such as the beaked whales and the sperm whales. 73 species of toothed whales are described. They are one of two living groups of cetaceans, the other being the baleen whales (Mysticeti), which have baleen instead of teeth. The two groups are thought to have diverged around 34 million years ago (mya).

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<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">Hourglass dolphin</span> Species of mammal

The hourglass dolphin is a small dolphin in the family Delphinidae that inhabits offshore Antarctic and sub-Antarctic waters. It is commonly seen from ships crossing the Drake Passage but has a circumpolar distribution.

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

The Ganges river dolphin is a species of freshwater dolphin classified in the family Platanistidae. It lives in the Ganges and related rivers of South Asia, namely in the countries of India, Nepal, and Bangladesh. It is related to the much smaller Indus river dolphin which lives in the Indus River in Pakistan and the Beas River of northwestern India.

<span class="mw-page-title-main">Evolution of cetaceans</span>

The evolution of cetaceans is thought to have begun in the Indian subcontinent from even-toed ungulates (Artiodactyla) 50 million years ago (mya) and to have proceeded over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla and branched off from other artiodactyls around 50 mya. Cetaceans are thought to have evolved during the Eocene, the second epoch of the present-extending Cenozoic Era. Molecular and morphological analyses suggest Cetacea share a relatively recent closest common ancestor with hippopotami and that they are sister groups. Being mammals, they surface to breathe air; they have five finger bones (even-toed) in their fins; they nurse their young; and, despite their fully aquatic life style, they retain many skeletal features from their terrestrial ancestors. Research conducted in the late 1970s in Pakistan revealed several stages in the transition of cetaceans from land to sea.

<span class="mw-page-title-main">Cetruminantia</span> Taxonomic clade

The Cetruminantia are a clade made up of the Cetancodontamorpha and their closest living relatives, the Ruminantia.

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

The baiji is a possibly extinct species of freshwater dolphin native to the Yangtze river system in China. It is thought to be the first dolphin species driven to extinction due to the impact of humans. This dolphin is listed as "critically endangered: possibly extinct" by the IUCN, has not been seen in 20 years, and several surveys of the Yangtze have failed to find it. In China, the species is also called the Chinese river dolphin, Yangtze river dolphin, Yangtze dolphin and whitefin dolphin. Nicknamed the "Goddess of the Yangtze", it was regarded as the goddess of protection by local fishermen and boatmen. It is not to be confused with the Chinese white dolphin or the finless porpoise. This is the only species in the genus Lipotes.

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

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<span class="mw-page-title-main">Indus river dolphin</span> Dolphin species found in the Indus River

The Indus river dolphin is a species of freshwater dolphin in the family Platanistidae. It is endemic to the Indus River basin in Pakistan and Beas River in northwestern India. This dolphin was the first discovered side-swimming cetacean. It is patchily distributed in five small, sub-populations that are separated by irrigation barrages.

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

Arktocara is an extinct genus of river dolphin from the Oligocene epoch of Alaska, containing one species, A. yakataga. Having been discovered in 25-million-year-old strata near the 60th parallel north, it is perhaps the oldest-known crown toothed whale and the northmost river dolphin discovered. It was a member of the now-extinct family Allodelphinidae, along with the genera Allodelphis, Goedertius, Ninjadelphis, and Zarhinocetus. It measured approximately 2.26 or 2.28 meters, comparable to its closest living relative, the South Asian river dolphin, which measures 2.4 meters (7.9 ft). However, the animal probably had an elongated beak and neck, so it may have been longer. The animal is known only from a partially preserved skull. Its ecology may have been similar to the modern-day Dall's porpoise, and it may have competed with contemporaneous delphinoids. Its remains were found in the Poul Creek Formation, which has also yielded several mollusk species.

<i>Pebanista</i> Extinct genus of freshwater dolphins

Pebanista is an extinct genus of platanistid "river dolphin" that lived during the Early to Middle Miocene in Peru. As a member of the Platanistidae, Pebanista is most closely related to the extant Ganges and Indus river dolphins (Platanista) of South Asia and shares no close relation to the modern Amazon river dolphin that inhabits the same region today. Like its close relatives, Pebanista possesses enlarged crests that would have covered the melon in life, possibly helping to focus their biosonar while hunting in murky waters. Pebanista further stands out as being the largest "river dolphin" yet discovered, reaching lengths between 2.8–3.47 m at minimum, much larger than the biggest recorded freshwater cetaceans of today. Given its relatively robust if elongated snout, it is thought that Pebanista was an active predator, profiting from the rich prey selection available to it in the enormous Pebas wetlands that covered South America during the early parts of the Miocene. Only a single species of Pebanista is known so far: P. yacuruna.

References

  1. ↑ "Platanista Wagler 1830 (toothed whale)". Paleobiology Database. Archived from the original on 12 December 2021. Retrieved 26 March 2018.
  2. ↑ Wilson, D. E.; Reeder, D. M., eds. (2005). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Johns Hopkins University Press. ISBN   978-0-8018-8221-0. OCLC   62265494.
  3. 1 2 3 4 5 6 7 8 9 10 11 12 Braulik, G. T.; Archer, F. I.; Khan, U.; Imran, M.; Sinha, R. K.; Jefferson, T. A.; Donovan, C.; Graves, J. A. (2021). "Taxonomic revision of the South Asian River dolphins (Platanista): Indus and Ganges river dolphins are separate species". Marine Mammal Science. 37 (3): 1022–1059. Bibcode:2021MMamS..37.1022B. doi: 10.1111/mms.12801 . hdl: 10023/21691 .
  4. ↑ "Platanista". Merriam-Webster.com Dictionary. Archived from the original on 22 September 2022. Retrieved 22 September 2022.
  5. ↑ Pilleri, G.; Marcuzzi, G.; Pilleri, O. (1982). "Speciation in the Platanistoidea, systematic, zoogeographical and ecological observations on recent species". Investigations on Cetacea. 14: 15–46.
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  7. ↑ Rice, D. (1998). Marine Mammals of the World: Systematics and Distribution. Society for Marine Mammalogy. p. 92. ISBN   9781891276033.
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  9. 1 2 Hamilton, H.; Caballero, S.; Collins, A. G.; Brownell, R. L. Jr. (2001). "Evolution of river dolphins". Proceedings: Biological Sciences. 268 (1466): 549–556. doi:10.1098/rspb.2000.1385. JSTOR   3068225. PMC   1088639 . PMID   11296868.
  10. ↑ Gatesy, John; Geisler, Jonathan H.; Chang, Joseph; Buell, Carl; Berta, Annalisa; Meredith, Robert W.; Springer, Mark S.; McGowen, Michael R. (2012). "A phylogenetic blueprint for a modern whale" (PDF). Molecular Phylogenetics and Evolution. 66 (2): 479–506. doi:10.1016/j.ympev.2012.10.012. PMID   23103570. Archived (PDF) from the original on 9 June 2015. Retrieved 4 September 2015.
  11. ↑ McGowen, M. R.; Tsagkogeorga, G.; Álvarez-Carretero, S.; et al. (2020). "Phylogenomic resolution of the cetacean tree of life using target sequence capture". Systematic Biology. 69 (3): 479–501. doi:10.1093/sysbio/syz068. PMC   7164366 . PMID   31633766.
  12. ↑ Braulik, G.; Barnett, R.; Odon, V.; Islas-Villanueva, V.; Hoelzel, R.; Graves, J. A. (2015). "One species or two? Vicariance, lineage divergence and low mtDNA diversity in geographically isolated populations of South Asian river dolphin". Journal of Mammalian Evolution. 22 (1): 111–120. doi:10.1007/s10914-014-9265-6. S2CID   14113756.
  13. 1 2 Cassens, I.; Vicario, S.; Waddell, V. G.; Milinkovitch, M. C.; et al. (2000). "Independent adaptation to riverine habitats allowed survival of ancient cetacean lineages". PNAS. 97 (21): 11343–11347. Bibcode:2000PNAS...9711343C. doi: 10.1073/pnas.97.21.11343 . PMC   17202 . PMID   11027333.
  14. 1 2 3 4 5 6 7 8 Jefferson, Thomas A.; Webber, Marc A.; Pitman, Robert L. (2015). Marine Mammals of the World: A Comprehensive Guide to Their Identification (2nd ed.). Academic Press. pp. 346–349. ISBN   978-0-12-409542-7.
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  35. ↑ "National Aquatic Animal – National Symbols – Know India: National Portal of India". National Portal of India. Archived from the original on 22 January 2013. Retrieved 23 March 2012.
  36. ↑ "National Symbols of Pakistan". Government of Pakistan. Archived from the original on 28 November 2016. Retrieved 23 October 2016.
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