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| Ganges River dolphin Platanista gangetica (Lebeck, 1801) & Indus River dolphin Platanista minor Owen, 1853 in Braulik, Archer, Khan, .. et Graves, 2021. DOI: 10.1111/mms.12801 photos: Mansur/WCS Bangladesh (top) & WWF‐Pakistan (bottom) |
Abstract
South Asian river dolphins (Platanista gangetica) are among the most endangered of the world's cetaceans. The two subspecies in the family Platanistidae, Indus, and Ganges river dolphins (P. g. minor and P. g. gangetica), are both threatened by dams and barrages, declining river flows, fisheries bycatch, and pollution. We examine differences in external and skull morphology between dolphins in each river system to clarify their taxonomic status. Skulls from each river system could easily be differentiated using diagnostic differences in the shape of the frontal bones behind the nasals. This feature was present in all individuals irrespective of size, age, and sex. Ganges river dolphins are sexually dimorphic with females larger than males, but there was no evidence of dimorphism in the small sample of Indus river dolphins. There were no mitochondrial DNA haplotypes shared between the two river systems, and five fixed differences suggested a long‐term (approximately 0.55 million years) absence of gene flow. Diagnosable differences in morphological and genetic characteristics indicate long‐term reproductive as well as geographic isolation of Indus and Ganges river dolphins. We conclude that Indus and Ganges river dolphins should each be recognized as distinct species, and elevate the Indus subspecies, Platanista gangetica minor, to species level, Platanista minor Owen, 1853. Formal redescriptions are provided for both species.
Keywords: endangered species, river dolphins, speciation, taxonomy
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| Close up images of three skulls from the Ganges and three from the Indus illustrating the extension anteriorly and to the left of the frontal suture in Ganges River dolphins and how it differs clearly from animals in the Indus. |
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| Photograph of surfacing Indus River dolphin (Platanista minor) and Ganges River dolphin (Platanista gangetica) (photo credit: top - WWF‐Pakistan; bottom - Mansur/WCS Bangladesh). |
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| Dorsal, ventral, and lateral photos of a Ganges River dolphin skull, SMNH45648 from the Stuttgart Germany Collection. |
Order Cetartiodactyla Montgelard, Catzefils and Douzery, 1997
Cetacea Brisson, 1762
Odontoceti Flower, 1867
Superfamily Platanistoidea Gray, 1863
Family Platanistidae Gray, 1846
Genus Platanista Wagler, 1830
Platanista gangetica (Lebeck, 1801)
Diagnosis: The skulls can be differentiated from those of P. minor by the presence of a projection at the frontal suture above the nasals and behind the maxillary crests (Figure 4). While there is some overlap in tooth counts between Indus and Ganges river dolphins, all skulls with less than 30 teeth in the upper tooth rows are Ganges river dolphins. The Ganges river dolphin has three unique mtDNA haplotypes (HAP4‐6, see Braulik, Barnett, et al., 2015, GenBank accession numbers KJ629311‐13) with five fixed differences separating it from the Indus river dolphin.
Etymology: This species is known as the Ganges river dolphin after the river system from which it was described. We recommend the English common name Ganges river dolphin for this species.
It is known by many different local names within its range including, Susu (popular), Soons/Soans/Soos (Hindi and dialects), Shushuk (Bengali), Hiho/Hihu (Assamese), Bhagirath, Socho (Hindi/Maithili: eastern Bihar), Shus or Suongsu (Nepali), Shishumar (probable medieval name in Sanskrit), Pani Suar (name during the Mughal period).
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| Dorsal, ventral, and lateral photos of an Indus River dolphin skull SMNH45643, the Platanista indi neotype (Pilleri & Gihr, 1977), from the Stuttgart Germany, Collection. |
Platanista minor Owen, 1853
Diagnosis: Indus river dolphin skulls can be differentiated from those of the Ganges river dolphin by the absence of a projection at the frontal suture above the nasals and behind the maxillary crests on the skull (Figure 4). While there is some overlap in tooth counts between Indus and Ganges river dolphins, all skulls with more than 33 teeth in the upper tooth rows are Indus river dolphins. The Indus river dolphin has three unique mtDNA haplotypes (HAP1‐3, see Braulik, Barnett, et al., 2015, GenBank accession numbers KJ629309, KJ629310 & AJ554058) with five fixed differences separating it from the Ganges river dolphin.
Etymology: We recommend the English common name Indus river dolphin for the species. It is known as bhulan in the local languages of Pakistan, and northwest India, where it occurs.
CONCLUSIONS:
Indus and Ganges river dolphins are the sole remaining relicts of the entire Platanistoidea cetacean superfamily and thus from the perspective of evolutionary distinctiveness their conservation is of key importance. The recognition of two species of Platanista detailed above requires a re‐evaluation of their conservation status. Both are currently listed as Endangered on the IUCN Red List and are already among the most endangered of all cetaceans. There is now an urgent need to elevate these species to a higher level of conservation concern and priority. This is especially true for the Indus river dolphin, which has declined drastically throughout most of its range due to its massive altered and degraded habitat (Braulik, Noureen et al., 2015). The Ganges river dolphin, although presently more numerous, is under great threat due to proposed and ongoing large infrastructure projects that have the potential to destroy large swaths of the most important habitat for the species (Kelkar, 2017).
Gill T. Braulik , Frederick I. Archer, Uzma Khan, Mohammad Imran, Ravindra K. Sinha, Thomas A. Jefferson, Carl Donovan and Jeff A. Graves. 2021. Taxonomic Revision of the South Asian River Dolphins (Platanista): Indus and Ganges River Dolphins are Separate Species. Marine Mammal Science. DOI: 10.1111/mms.12801