Delphinus rhinoceros - Rhinoceros Dolphin

This article has been updated significantly as of Jan 4, 2025. You can view previous versions of this article here: The Wayback Machine 

We will move on to other much smaller cetaceans, the dolphins: those of plate no. 11, which we will speak of first, have been seen at close range and sketched with sufficient accuracy so that those who have the faculty of capturing them can recognize the identity of the species. In our long navigation, we were within reach of seeing many of these animals around us, which seemed playfully to want to rival the speed of our floating machine; however, despite all our efforts to capture them, we were unable to do so; it is true that most often they offered themselves to our blows when the sea was rough or the ships progress was too rapid.

In the month of October, 1819, while sailing from the Sandwich Islands [Hawaii] to New South Wales, we saw, in 5° 28 north latitude, many dolphins (Plate 11, Figure 1), performing in troops around the vessel, their rapid evolutions: everyone on board was surprised, as we were, to see on their forehead a horn or fin curved backwards, like that of the back. The volume of the animal was about double that of the common porpoise, and the upper part of its body, up to the dorsal, was spotted black and white.

We endeavored to observe these dolphins during the whole time that they accompanied us: but although they often passed by, touching the prow of our corvette, having the upper part of their body out of the water, their head was so buried there that neither Mr. Arago nor we could distinguish whether their snout was short or elongated: their gait itself could not tell us anything in this regard; for they did not dash above the water like the other species. According to their very particular conformation, we have named them Rhinoceros Dolphins, Delphinus rhinoceros.

-        - Quoy and Gaimard, Voyage Autour Du Monde, 1824,page 86 of the edition I was reading from

 

Plate 11, mentioned above

Cropped illustration from the plate

The drawing copied in Der Cetacean Oder Walthiere, 1846

 

The Rhinoceros Dolphin is probably one of the best known “cryptid whales” today, alongside Giglioli’s Whale and the Alula Whale. However, the details of its discovery and description are somewhat messy. I’ve updated this post to clarify some of the points of contention I was too lazy to clarify in the last version.

The sighting is characterized by the dolphin’s bizarre double dorsal fin, strange blotchy coloring, and the fact that none of the dolphins observed raised their heads above the water. This supposed species has been the subject of a lot of speculation, and even its own paper authored by Michel Raynal and Jean-Pierre Sylvestre in 1991, Cetaceans With TwoDorsal Fins.

 

My drawing

This was an obvious entry to the series. As with the other entries, I followed the original description as closely as I could, and took some liberties to fill in the gaps. The white markings are pretty peculiar. The closest comparison that comes to mind is the Atlantic Spotted Dolphin, although their spots are much smaller and cover their entire bodies (not to mention, this dolphin was not sighted in the Atlantic). The reason I went with a round snout as opposed to a long beak is because all known toothed whales that approach the Rhino Dolphin’s size (Risso’s Dolphin, False Killer Whale, Pilot Whale on the larger end) all have round faces. I’m not sure if there’s an evolutionary reason for this, but it felt like a safe assumption.

Size

In the original description, Quoy and Gaimard note that “The volume of the animal was about twice that of the common porpoise” (“Le volume de l'animal étoit à-peu-près double de celui du marsouin ordinaire,”). Common porpoise is not a terribly precise unit of measurement. You could also argue that the volume being referred to is not very well defined either, but I am choosing to interpret volume as overall length and body mass.

Common porpoise could be interpreted two ways – either the authors were referring to the Harbour Porpoise, a species commonly found in Europe’s waters, or they could be using the term porpoise to refer to a dolphin, as many authors have in the past. In Raynal and Sylvestre’s 1991 paper, they go with the Harbour Porpoise; doubling its length puts the Rhinoceros Dolphin at around 3 meters, or 10 feet. However, in his 2021 paper Nomenclature of the dolphins[…], cetologist Tom Jefferson writes the following –

It was described as twice the size of a “common porpoise” (probably referring to Tursiops truncatus, which would make it about 5-7 m). (page 62)

Jefferson chooses to interpret common porpoise as Bottlenose Dolphin, for unspecified reasons. I was personally more inclined to believe that if common porpoise referred to a dolphin, it would be referring to Delphinus delphis, the Common Dolphin, so named for just how ubiquitous it is on the open ocean.

 

 

The only real way to clarify this would be to read the original source paper and gather the context in which marsouin ordinaire was used. I could not find this original paper back when I first wrote this blog post, but I’ve since found it and read the cetacean section, which is about 14 pages. All mentions of porpoises and dolphins are contained in this section. Given how the text refers to both porpoises and dolphins (on page 82, they alternatively use “dauphin ordinaire” to gauge the size of young baleen whales) I think Jean René Constant Quoy and Joseph Paul Gaimard, two well-traveled zoologists evidently invested in capturing and describing various cetacean species, likely differentiated between porpoises and dolphins. One line in particular cements this for me. At the beginning of the cetacean section, the authors go on a long and strangely heated tangent disagreeing with William Scoresby’s (correct) suggestion that whales do not expel jets of water from their blowholes but merely warm breath filled with condensation. In this tangent, they mention the following –

These animals will provide us with the most convincing and irrefutable proof to oppose to Mr. Scoresby's opinion: for, without doubt, if the visible jet were composed simply of air and condensed mucus, the porpoises which, in our countries, often come to breathe on the surface of the sea, would emit this vapour in a similar form, and in proportion to their size. (page 79)

If our countries refers to England and France (the homes of Scorseby and Quoy+Gaimard, respectively) this could only be referring to the Harbour Porpoise, the only porpoise species found in Europe.

And with that incredibly long-winded explanation, I personally feel that Raynal and Sylvestre’s size estimate of 3 meters for the Rhinoceros Dolphin is most accurate to what Q&G claim they saw. At the end of the day, given the unclear circumstances of the original sightings, Q&G’s word still cannot be taken entirely at face value.

 

Location

The species was spotted between Hawaii and New South Wales, 5°28'. The exact longitude (East/West position) is not given. The pin in the map below shows the correct latitude, but the longitude is totally speculative.

Naming

The Rhinoceros Dolphin has gone through several scientific name changes throughout history. They are, in a brief timeline:

• Delphinus rhinoceros, Quoy & Gaimard, 1824
• Oxypterus rhinoceros, R. P. Lesson, 1827
• Cetodipteros rhinoceros, Raynal and Sylvestre, 1991
• Delphinus rhinoceros (nomen dubium), Tom Jefferson, 2021

Back in the 19^th century, pretty much any cetacean that was not a Sperm Whale or baleen whale was dumped under the catch-all genus Delphinus. Everything from orcas to beaked whales lived under this genus for a while until scientists started getting pickier around the turn of the century. Delphinus is the obvious genus for Q&G to have assigned this whale at the time.

However, in 1827, R. P. Lesson, discoverer and namer of the Rough-Toothed Dolphin, reassigned the Rhinoceros Dolphin to the genus Oxypterus. Up until then, Oxypterus had contained only one species, Oxypterus mongitori (named by Rafinesque in 1814), a bizarre whale species that reportedly washed up in Sicily in 1743 and was drawn sometime after the fact. This species was named after its illustration more so than its original description, which depicts a bizarre fish-like creature with two dorsal fins. I’m sure I’ll cover this weird whale in a future instalment, but Raynal and Sylvestre also describe this whale in their paper if you’d like a bit more context.

 

You're telling me this didn't hold up to modern scrutiny??

 

Evidently, based on the number of appearances in Jefferson’s 2021 name catalogue, Lesson loved naming and renaming stuff, and the vast majority of these new names have been thrown out. However, Lesson did describe a few unusual whales whose synonymity is not immediately clear – his Delphinus minimus has already made an appearance on this blog, and you can expect more of his whales in future.

In their paper Cetaceans with two dorsal fins, Raynal and Sylvestre suggest the new scientific name Cetodipteros rhinoceros for the dolphin. They do not explain what the name means but my very weak grasp on Greek makes me inclined to believe “Cetodipteros” means “Whale (cetos) with two (di) wings (pteros)”. However, beneath my post about the Rhinoceros Dolphin on Twitter, Tyler Greenfield pointed out that even if the Rhinoceros Dolphin is confirmed to exist, the genus named Cetodipteros cannot be used for it.

 

Since Raynal & Sylvestre said “We would propose the name [...] if it would turn out to represent a new genus”, it is a conditional proposal and thus 'Cetodipterus' is an unavailable name according to ICZN Article 15.1.https://t.co/o1MdduU9ig

— Tyler Greenfield (@TylerGreenfieId) June 8, 2024

Speculation

Given the information I have, my personal gut feeling is that the dolphins spotted and Q&M and their crew were likely Risso’s Dolphins swimming in a tight formation, giving the illusion of dolphins with two dorsal fins. Risso’s Dolphins’ bodies are often covered in white scars caused by other dolphins, and their size (3-4ft), range and behaviour align with the Rhinoceros Dolphin sighting.

James M. Maley, Wikimedia Commons

Other common theories include that the crew sighted mothers swimming close to their calves or that the animals sighted were possibly sharks (Jefferson mentions this theory himself).

One of my followers on Twitter made the suggestion to perhaps the Rhinoceros Dolphin was a Blaineville's Beaked Whale. If Jefferson’s size estimate of 5-7 meters is correct, this theory would fit nicely, considering the teeth of this whale which jut up from the lower jaw can form a facial horn of sorts. (In the previous version of this article I claimed that Blaineville’s Beaked Whales never approach boats. This assumption of mine appears to be incorrect.)

Blainville's Beaked Whale

Bonus sketch

I was very eager to draw this dolphin. Maybe too eager. I was not totally confident in my ability to read lat/long and initially took “between the Sandwich Islands and New South Wales” at face value and assumed the sighting took place in the subantarctic Pacific ocean. My initial sketch was based on the Short Finned Pilot Whale because this is a species found in this area. As it turns out, “Sandwich Islands” is the old name for Hawaii. While Hawaii’s current name would be imposed by Kamehameha I in 1782, it would not be called this officially in writing until 1849.