The Rhinoceros Dolphin (Delphinus rhinoceros), is an unrecognized species of dolphin said to have two dorsal fins.
Off the coast of the Sandwich Islands and New South Wales, Jean-Rene Quoy and Joseph Gaimard allegedly discovered a new type of dolphin. Described as Delphinus rhinoceros, these are dolphins - or dolphin-like whales - which possess two dorsal fins. One is near the head, where the neck would be on terrestrial animals, and the other is farther back than usual. These have a somewhat large size, and are black with large white blotches. However, their existence was never proven and their identity remains unknown. They may belong to a new genus, in which case the name Cetodipterus has been proposed by Michel Raynal, but the name is still up for debate.
- Delphinus rhinoceros, given by J. R. C. Quoy and J. P. Gaimard in 1824.
- Cetodipteros rhinoceros, given by Michel Raynal in 1991.
- Michel Raynal points out that the animal might just as well be an unknown beaked whale as a dolphin.
- A calf pressed tightly against its mother might have been mistaken for a second dorsal fin in the nearest animal; that all the animals in the school had a similar protrusion may have been a false assumption.
- Giglioli's Whale another unrecognized cetacean with two dorsal fins.