The Rhinoceros Dolphin (Delphinus rhinoceros), is an unrecognized species of dolphin said to have two dorsal fins. The species was first described by Jean-Rene Quoy and Joseph Gaimard [1] who in 1824 spotted a pod of the dolphins while sailing from the Sandwich Islands (now Hawaii) to New South Wales, Australia. In 1991, Michel Raynal suggested the new species name Cetodipterus rhinoceros.
The original illustration. The dolphins did not raise their heads above the water.
In the month of October 1819, going from the Sandwich Islands to New South Wales, we saw at 5° 28' north latitude many dolphins performing in troupes around the ship: everyone on board was surprised, like us, to see on their forehead a horn or fin curved backwards, as well as that on the back; the volume of the animal was almost double that of the common porpoise, and the top of its body, up to the dorsal, was spotted with black and white.
We focused on observing these dolphins throughout the time they accompanied us; but although they often came close to touching the prow of our corvette, having their upper bodies out of the water, their heads were so buried there that neither Mr. Arago nor we could distinguish whether their muzzle was short or elongated; their appearance could tell us nothing in this regard because they do not soar above the waters like other species. Based on their very particular conformation, we named them Rhinoceros Dolphins (Delphinus rhinoceros)
- Original 1824 description, translated from French
The dolphins Quoy and Gaimard saw did not lift their heads above the water as they swam alongside the ship, limiting the observers' view of the animals. However, the front half of their body is described as having spotted black and white skin, with an extra dorsal fin located near the head region. Their size is described as double that of the common porpoise.
This supposed species has not been sighted since 1819, leaving its existence dubious.
Scientific names[]
Delphinus rhinoceros, given by J. R. C. Quoy and J. P. Gaimard in 1824.
Cetodipteros rhinoceros, given by Michel Raynal in 1991.
Theories and discussion[]
Various explanations for the Rhinoceros Dolphin have been put forward, among the most common being that the "dolphins" were actually sharks (which have two dorsal fins) or that the original pod that was sighted were swimming very closely together, giving the illusion of whales having two dorsal fins.
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.
