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taxonomic classification of cetaceans that has become standard in the field, found that there
were insufficient morphological differences to warrant distinction at the species level. Thus
one species is recognized in the genus
Platanista
and currently the Ganges River dolphins are
Platanista gangetica gangetica
and the Indus River dolphins of Pakistan are
Platanista
gangetica minor.
The species has many primitive characters and is one of the charismatic
megafauna of the rivers of the Indian subcontinent. The animal is facing threats of extinction
in its entire distribution range due to overexploitation and habitat degradation caused by
various anthropogenic pressures. In most of the rivers, its distribution range has shrunk in the
last couple of decades.
Phylogenetic Position of the Ganges River Dolphin
The four genera of classical river dolphins are associated with six separate great river
systems on three subcontinents and have been lumped into a single taxon (family
Platanistidae or super family Platanistoidea) based on their similarity in some morphological
characters. This grouping has been proven unreasonable by all modern phylogenetic analyses
(Yan et al., 2005). Muizon (1984, 1988) regarded
Platanista
as only distantly related to the
other three, and Heyning (1989) also restricted Platanistoidea to
Platanista
. In cladistic
analysis, the family Platanistidae fell into a clade with the extinct families Squalodelphinidae.
Delpiazinidae, Waipatiidae, and Squalodontidae (Fordyce & Barnes, 1994; Fordyce &
Muizon, 2001). Studies on cetacean phylogeny using DNA sequence data have become very
prominent since the 1990s. Arnason & Gullberg (1996) first supplied molecular evidence
(Cyt b) with the view that
Platanista
had no affinity to
Inia
and
Pontoporia
. Yang & Zhou
(1999) first included all of the four classical river dolphins in their studies. Subsequently,
Cassens et al. (2000), Hamilton et al. (2001), Nikaido et al. (2001), and Yang et al. (2002)
analyzed phylogeny of river dolphins using different DNA markers respectively. In all
analyses mentioned above,
Platanista
was identified as an independent lineage of
odontocetes, and had no affinity to the nonplatanistoid river dolphins. The overview that the
classical river dolphins including Platanistidae and three other families are an unnatural group
has been widely accepted. Yan et al. (2005), in their analyses, split classical river dolphins
into two distinct lineages,
Platanista
and
Lipotes
+ (
Inia
+
Pontoporia
), having no sister
relationship with each other and opined that such a phylogenetic pattern strongly supports the
paraphyletic relationship of the classical river dolphins.
Numerous arrangements have been proposed for the phylogenetic relationships of the
world's river dolphins to one another and to other odontocete cetaceans. Based on
phylogenetic analysis of three mitochondrial genes for 29 cetacean species, Hamilton et al.
(2001) concluded that the four genera of freshwater dolphins represent three separate, ancient
branches in odontocete evolution. Further, they suggested that ancestors of the four extant
river dolphin lineages colonized the shallow epicontinental seas that inundated the Amazon,
Parana, Yangtze and Indo-Gangetic river basins, subsequently remaining in these extensive
waterways during their transition to freshwater within the Late Neogene trend of sea-level
lowering
While studying the molecular phylogeny of river dolphins, Guang & Kaiya (1999)
observed that the difference between
cyt b
sequence of Ganges River dolphin and Indus River
dolphin was very small, which supported that Ganges River dolphin (
P. g. gangetica
) and
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