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In the 1970s, scientists classified Indian river dolphins as separate species based on variations in skull and vertebral structures, as well as differences in blood proteins and lipids. However, these findings faced criticism due to limited sample sizes and a lack of statistical analysis. By the late 1990s, the two populations were once again regarded as subspecies of a single species. A mitochondrial DNA study conducted in 2014 indicated that there were not enough differences to justify their separation as distinct species. Nevertheless, a study in 2021 reassessed the two populations and identified significant genetic divergence along with considerable differences in skull morphology, ultimately confirming that they are indeed separate species. | In the 1970s, scientists classified Indian river dolphins as separate species based on variations in skull and vertebral structures, as well as differences in blood proteins and lipids. However, these findings faced criticism due to limited sample sizes and a lack of statistical analysis. By the late 1990s, the two populations were once again regarded as subspecies of a single species. A mitochondrial DNA study conducted in 2014 indicated that there were not enough differences to justify their separation as distinct species. Nevertheless, a study in 2021 reassessed the two populations and identified significant genetic divergence along with considerable differences in skull morphology, ultimately confirming that they are indeed separate species. | ||
=== Evolution === | |||
Indian river dolphins represent the sole surviving members of the family ''Platanistidae'' and the superfamily ''Platanistoidea''. They do not share a close evolutionary relationship with other river dolphins belonging to the families ''Lipotidae'', ''Pontoporiidae'', and ''Iniidae'', which have all adapted to freshwater environments independently. The accompanying cladogram, derived from the work of Gatesy and colleagues (2012) and McGowen and colleagues (2020), illustrates the evolutionary relationships between Indian river dolphins and other existing families of toothed whales. | |||
{{Clade|style=font-size:85%;line-height:100%;width:580px; | |||
|label1='''[[Toothed whales]]''' | |||
|1={{Clade | |||
|1={{Clade | |||
|1=[[Sperm whale]]s (Physeteridae) [[File:Physeter macrocephalus NOAA.jpg|50 px]] | |||
|2=[[Dwarf sperm whale]]s (Kogiidae) [[File:Kogia sima (transparent background).png|50 px]] | |||
}} | |||
|2={{Clade | |||
|1='''Indian river dolphins''' (Platanistidae) [[File:Ganges.png|50 px]] | |||
|2={{Clade | |||
|1=[[Beaked whale]]s (Ziphiidae) [[File:Ziphius cavirostris NOAA.jpg|50 px]] | |||
|2={{Clade | |||
|label1=South American river dolphins | |||
|1={{Clade | |||
|1=[[Pontoporiidae]] [[File:Pontoporia blainvillei.jpg|50 px]] | |||
|2=[[Iniidae]] <span style="{{MirrorH}}">[[File:Inia geoffrensis.jpg|50 px]]</span> | |||
}} | |||
|label2=[[Delphinoidea]] | |||
|2={{Clade | |||
|1=[[Oceanic dolphins]] (Delphinidae) [[File:Orcinus orca NOAA 2.jpg|50 px]] | |||
|2={{Clade | |||
|1=[[Porpoise]]s (Phocoenidae) [[File:Vaquita swimming through the void. (Phocoena Sinus).png|50 px]] | |||
|2=[[beluga whale|Belugas]], [[narwhal]]s (Monodontidae) [[File:Delphinapterus leucas NOAA.jpg|50 px]] | |||
}} }} }} }} }} }} }} | |||
==References== | ==References== | ||