More a tadpole than a fish?

I had an excellent summer for reading. No internet, few disturbances and quite a bit of rain. Thanks to these fortunate circumstances I finally read a few books I have been postponing, including “Twenty thousand leagues under the sea” (fun but not very memorable) and “Moby Dick” (excellent!).

Reading these novels next to each other I amused myself by comparing their descriptions of whales, especially cachalots (sperm whales). Moby Dick is naturally full of descriptions of whales but I was particularly interested in the following section:

“First: The uncertain, unsettled condition of this science of Cetology is in the very vestibule attested by the fact, that in some quarters it still remains a moot point whether a whale be a fish. In his System of Nature, A.D. 1776, Linnæus declares, “I hereby separate the whales from the fish.” But of my own knowledge, I know that down to the year 1850, sharks and shad, alewives and herring, against Linnæus’s express edict, were still found dividing the possession of the same seas with the Leviathan.

The grounds upon which Linnæus would fain have banished the whales from the waters, he states as follows: “On account of their warm bilocular heart, their lungs, their movable eyelids, their hollow ears, penem intrantem feminam mammis lactantem,” and finally, “ex lege naturæ jure meritoque.” I submitted all this to my friends Simeon Macey and Charley Coffin, of Nantucket, both messmates of mine in a certain voyage, and they united in the opinion that the reasons set forth were altogether insufficient. Charley profanely hinted they were humbug.”

Having thus dismissed Linnæus arguments the narrator continues by defining a whale as “a spouting fish with a horizontal tail”. The truth of this statement is of course dependent on your definition of fish but I would side with Linnæus here and argue that a whale is not a fish.

In contrast we have the following description of cachalots from captain Nemo in “Twenty thousand leagues under the sea”, amusingly just after he declared the hunting of Baleen whales (unless fresh meat for the crew was needed) a “murderous pastimes”.

“Those are sperm whales, dreadful animals that I’ve sometimes encountered in herds of 200 or 300! As for them, they’re cruel, destructive beasts, and they deserve to be exterminated. […] We’ll take no pity on these ferocious cetaceans. They’re merely mouth and teeth!”

The main character in “Twenty thousand leagues under the sea”, Professor Aronnax, agrees with this assessment and adds: “The sperm whale is an awkward animal, more tadpole than fish, as Professor Frédol* has noted.” which I find a glourious insult to the world’s largest toothed whale. I already argued that a whale is no fish, the intriguing question now is whether it is also true that a cachelot is more a tadpole than a fish?

To answer that question I used science and internet, more specifically the site timetree.org which gives the time of divergence of two species, that is the time when their evolutionary ancestors separated. To test whether a cachelot is more a tadpole than a fish I searched for the divergence time of the following species:

• Physeter macrocephalus or cachelot (sperm whale)
• Rana temporaria or common frog as a representative of tadpoles.
• Gadus morhua or cod as a representative of fishes.

Fittingly all three species got their scientific names from Linnæus in his Systema Naturae (1758).

From timetree.org I learnt that the evolutionary branches of cachelot and common frog got separated around 352 million years ago, in the Early Carboniferous. Cachelot and cod on the other hand got separated already 435 million years ago, during the Silurian, and are therefore less closely related. It would thus be at least partly fair to call a cachelot “more tadpole than fish”

The more difficult question of whether a tadpole is more a cachelot than a fish I leave as an open question for the comment field.

*Le monde de la mer by Alfred Frédol. I can’t read French but based on a Google translation of Frédol’s text I believe he only described the general appearance of the cachalot when he likened it to a tadpole. Still an insult but a bit more reasonable.