The Rhinoceros Dolphin

In 1820, Quoy and Gaimard described two species of dolphins from sightings, now believed to be the first documented encounters with Hourglass Dolphins (Lagenorhynchus cruciger). In 1826, Hourglass Dolphins were described again (as Delphinus bivittatus‘) from far more detailed sightings by Lesson and Garnot (Jardine 1837). Finally* in 1830, d’Orbigny acquired a specimen and preserved its skull in a museum (True 1889), ending the 10 year run as a… cryptid, of sorts. In contrast, Quoy and Gaimard also described ‘delphinus rhinoceros‘ from a sighting and the species is now regarded as a nomen dubium, having never been observed again despite the striking feature of a supernumerary dorsal fin or horn on its head. It would seem likely that Quoy and Gaimard were mistaken, but what did they actually see?

* To be fair, the taxonomy of Hourglass and other Southern Hemisphere dolphins was confused for a long time after. For instance, Hourglass Dolphins were named from sightings again (as ‘Lagenorhynchus wilsoni‘)… in 1915!

Quoy and Gaimard’s ‘delphinus rhinoceros’. From Jardine (1837)

Michel Raynal documented some possible explanations – Georges Cuvier proposed it may have been an optical illusion and Richard Ellis suggested it may have been a dolphin with a remora stuck on its head. Raynal himself suggested it may have been misobserved somersault behavior (with the first fin being a flipper and the second being a fluke) but dismissed it as unlikely. Markus Bühler pointed out that one dolphin’s deformed jaw curiously resembles the oddly placed fin or horn of the Rhinoceros Dolphin. Supernumerary dorsal fins are apparently a genuine abnormality, judging from photographs of twofinned humpbacks and Snooky the dolphin, however none have turned up a considerable distance from the normal fin, let alone on the head. Raynal and Sylvestre (1991) argued that since Quoy and Gaimard observed multiple individuals exhibiting the morphology, a distinct species (‘Cetodipterus rhinoceros‘†) would be more probable than a pod of disfigured individuals. The authors didn’t appear to consider the possibility that the cause was genetic and that the individuals may have been some freakish inbred clan, the Blue Fugates of the seas, if you will. There is another possibility – that Quoy and Gaimard observed specimens which were neither deformed nor members of an unknown species or population.

† Renamed since Delphinus is now far less inclusive and the cryptid may not have been a dolphin. ‘Oxypterus rhinoceros‘ is another synonym proposed by Lesson (Jardine 1837) however the type species of the genus (Rafinesque’s ‘Oxypterus mongitori‘) was vaguely described with a second dorsal fin (and scales, gill-slits, and an anal fin) being present only in a dubious secondhand illustration.

At some point, Raynal discussed the possibility that the ‘Rhinoceros Dolphin’ may actually be a beaked whale (Eberhart 2002) which made me realize there’s already a species with bizarre fin-like or horn-like projections coming out of its head – male Mesoplodon densirostris. Let’s see how this hypothesis stacks up with Quoy and Gaimard’s written account:

Dans le mois d’octobre 1819, en allant des îles Sandwich à la Nouvelle-Galles du Sud, nous vîmes, par 5° 28′ de latitude N.,

The encounter occurred in October 1819, somewhere between Hawai’i and New South Wales at 5° 28′ North. Quoy and Gaimard were probably unaware of Mesoplodon densirostris since it was described in 1817, the year they set sail. The holotype was a partial rostrum, so even if Quoy and Gaimard somehow learned of the whale, they would have been unaware of its external appearance. Mesoplodon densirostris is believed to inhabit tropical through warm temperate waters across the world (MacLeod et al 2006), so the vague locality is not an issue.

beaucoup de dauphins (planche 11figure 1), exécutant en troupes,

“Many” dolphins in “troops” were observed. One study of 19 encounters with M. densirostris off Hawai’i found that groups are usually small (median = 3, mean = 3.53) with a maximum of 9 individuals (McSweeney et al. 2007). This is a potential problem for the M. densirostris hypothesis and it’s a real shame that Quoy and Gaimard didn’t give a rough idea of the total number – would 9 individuals be “beaucoup” for 19th Century Frenchmen? It is curious that the illustration shows only a single individual, which, coupled with the ambiguous count, makes me wonder if only one individual investigated the ship while the others remained some distance away. It’s worth noting that groups of M. densirostris were not observed to have more than two males (McSweeney et al. 2007).

autour du vaisseau, leurs rapides évolutions:

This appears to state that the animals were changing direction around the ship. This is potentially problematic for M. densirostris since it has two projections and not one. Since the illustration shows an animal from the side, this makes me wonder if it was circling the ship, and maintaining the illusion of a single horn or fin.

tout le monde à bord fut surpris, comme nous, de leur voir sur le front une corne ou nageoire recourbée en arrière, de même que celle du dos.

To everyone’s surprise, there was a horn or curved dorsal fin on their foreheads, in addition to a dorsal fin on their backs. Raynal & Sylvestre (1991) translate “sur le front” as “on their snouts” and argue that the illustration demonstrates the supernumerary dorsal fin was actually behind the head. The illustration of course doesn’t show any demarcation indicating where the head is located and shows a cetacean with fairly dubious proportions, probably warped so both fins could be visible at once. I don’t think the illustration is useless, just that Quoy and Gaimard’s statements should be given precedence.

Le volume de l’animal étoit à-peu-près double de celui du marsouin ordinaire,

The animals had a volume twice that of a “common porpoise”, presumably the Harbor Porpoise (Phocoena phocoena). Raynal & Sylvestre (1991) interpret “volume” as “length” and suggest Quoy and Gaimard estimated ‘delphinus rhinoceros’ to be ~3 meters in length. However, Quoy and Gaimard (1824) used “longueur” for length and “volume” for volume in their book, so they apparently (and improbably) estimated ‘delphinus rhinoceros’ to weight around 100-120 kg. This would make it ~2 meters in length if shaped like a porpoise. It’s worth noting that estimating size at sea is notoriously difficult, making Quoy and Gaimard’s already ambiguous estimate fairly useless. M. densirostris has a mean length of 4.15 meters (MacLeod 2005), by the way.

et le dessus de son corps , jusqu’à la dorsale, étoit tacheté de noir et de blanc.

The animals were spotted black and white. The illustration clarifies that these are irregular white spots on a dark background. This of course looks strongly reminiscent of the coloration of M. densirostris, the white blotches being scars from Cookiecutter Sharks (which Quoy and Gaimard described).

Nous nous attachâmes à observer ces dauphins pendant tout le temps qu’ils nous accompagnèrent : mais quoiqu’ils- passassent souvent à toucher la proue de notre corvette,

The group accompanied the boat, often approaching close enough to touch the bow of the ship.

ayant le haut du corps hors de l’eau, leur tête y étoit tellement enfoncée, que ni M. Arago, ni nous, ne pûmes distinguer si leur museau étoit court ou alongé: leur allure même ne put rien nous indiquer à cet égard; car ils ne s’élançoient point au-dessus des eaux comme les autres espèces.

Only the top part of the animals were held out of water. The head was depressed and it was not possible to determine if the snout was short or elongated. The depressed head is certainly consistent with the flat melon of mesoplodonts. I cannot find a translation for the word “élançoient”… I hope it’s not important.

D’après leur conformation toute particulière, nous les avons nommés dauphins rhinocéros [ delphinus rhinoceros ].

They shall be called… Rhinoceros Dolphins!

The notion that Rhinoceros Dolphins are a species which hasn’t been seen in 190 years is… a bit much, especially considering their unmistakable profile and lack of fear of vessels. The only supporting evidence for this cryptid are dolphin figurines Raynal has documented – the purported “dorsal fins” on the head look like a normal continuation of the melon to me. Mesoplodon densirostris isn’t a perfect candidate, but the similarities are suspicious and we already know Quoy and Gaimard aren’t perfect observers. In order for the beaked whales to work as a candidate, Quoy and Gaimard would have to observe a large group where one or two males investigated the ship by circling it, remaining in lateral view, creating the illusion of having one horn or head-fin and leading the authors to believe the others had them too.

There are still some big surprises out there, and recently there has been a major beaked whale discovery in the tropical Pacific – the resurrection of Mesoplodon (ginkgodens?) hotaula.


Eberhart, G. M. (2002) Mysterious Creatures: A Guide to Cryptozoology.

Jardine, W. (1837) The Natural History of the Ordinary Cetacea or Whales. Available.

MacLeod, C. D. et al. (2006) Known and inferred distributions of beaked whale species (Cetacea: Ziphiidae). Journal of Cetacean Research and Management 7(3), 271–286. Available.

MacLeod, C. D. (2005) Niche Partitioning, Distribution And Competition In North Atlantic Beaked Whales. Thesis for Doctor of Philosophy at the University of Aberdeen, Aberdeen, UK. Available.

McSweeney, D. J. et al. (2007) Site fidelity, associations and movements of Cuvier’s (Ziphius cavirostris) and Blainville’s (Mesoplodon densirostris) beaked whales off the island of Hawai’i. Marine Mammal Science 23(3), 666-687. Available.

Raynal, M. & Sylvestre, J-P. (1991) Cetaceans with two dorsal fins. Aquatic Mammals 17.1, 31-36. Available.

Quoy and Gaimard. (1824). Voyage autour du monde.. l’Oranie et la Physicienne… ZoologieAvailable.

True, F. W. (1889) A Review of the Family Delphinidæ. Bulletin of the United States National Museum 36. Available.