It was with some joy that I recently read of a newly discovered species of river dolphin, Inia araguaiaensis (Araguaian river dolphin or Araguaian boto).A close relative of former AOTW the Amazon boto, scientists taking a close look at the dolphins living in the Aruguaia–Tocantins river system noticed that they were a bit smaller than their relatives in the Amazon and had different jaw morphology. Some genetic studies revealed that the two populations had been separated for more than 2 million years and were likely different enough to be recognised as different species.
Animal of the Week isn't always (some would say "ever") a barrel of laughs. While I've made a lot of posts about new species described and discovered, I've had occasion to note a couple of extinctions along the way. The baiji is perhaps the most memorable no-longer species to feature as AOTW—this freshwater dolphin, erstwhile inhabitant of China's Yangtse river is thought to have gone extinct around 2006—the only species of whale or dolphin to be declared extinct in modern times, probably not the last.
River dolphins are not all c
losely related and are not confined to freshwater habitats. The true river dolphins (the botos, the plata dolphin, the baiji, and the south Asian river dolphin) are thought to represent a primitive group of species that once was also widely spread in marine habitats before the more modern dolphins arose and usurped them. The tucuxi lives in the Amazon and Orinoco rivers, but is more closely related to marine dolphins than to the river dolphins.
While there's some debate about whether the Araguaian boto is sufficiently different from the Amazon boto to be a completely separate species, but hey, give them another 2 million years and they will be.
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