The Rhinoceros Dolphin is an unknown cetacean, reported from North Pacific Ocean.
Length, about 10 feet. Upper body spotted black and white. Has two dorsal fins—a standard dorsal fin in the center of the back, supplemented by a second fin close to the neck.
The naturalists Quoy and Gaimard observed a school of dolphins with two dorsal fins in the North Pacific, possibly in the neighborhood of Palmyra Atoll, in October 1819. They did not get a good look at the animal's heads, which were under water.
In April 1856, one or two dolphins with two dorsal fins were seen in a school of Common dolphins (Delphinus delphus) in Lantivet Bay, Cornwall, England.
- 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.