The tucuxi (Sotalia fluviatilis) in the Amazon River is another species descended from oceanic dolphins; however, it does not perfectly fit the label of 'facultative' either, as it occurs only in freshwater.
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In 1847, he and Paul Gervais compared it to "Delphinius geoffrensis" (=Amazon river dolphin, Inia geoffrensis), which had been described from a stuffed specimen in Lisbon, and the two were considered synonyms for more than a century.
The Boto, or Amazon River Dolphin, is also known to inhabit the Orinoco River system.