This is a summary: I hated people for thinking whales were fish -> I did a zoology degree -> Whales really are fish. So am I.
I feel like being truthful today.
So here's the thing.
When I was a child - a very precocious child, I might add, who at the age of seven would chastise the headmistress for getting dugongs and manatees confused (in fairness, she was an Aussie and ought to have known), I was that child who would never talk to a classmate again because they thought that the biggest fish in the sea was a blue whale.
The blue whale (Balaenoptera musculus) is the largest vertebrate known to have ever existed, but having lungs, a placenta and mammary glands (milk-producing breast tissues), every junior geek knows that it is firmly a mammal.
One degree later, I realise that I am wrong.
Here's why:
Biology teachers.
It is all because of Biology Teachers.
Biology teachers suck.
I'm not saying that because I had a Creationist(!!!!) Biology teacher from year 8 (I think) to year 10.
I'm not saying it because one of my biology teacher for A-level was so boring that half the class fell asleep during his lessons. The other biology teacher was awesome and wonderful and probably part walrus, so it hurts me to say it, but
Biology teachers suck.
This takes some explaining.
The first part of this explanation comes about 150 years ago, on the 22nd of November 1859, with the publication of a truly epic book by a person who I am incredibly fond of only for their scientific contributions and their beard, and would probably loathe as an individual (sorry Darwin, but killing things for fun is not good).
This marks the point where taxonomy went from being a filing system for diversity to being a science. It was the beginning of the scientific realisation that life on earth is all part of one big, happy, self-cannibalizing family.
Of course I have to mention good old Gregor Mendel, who gave us genetics and thus made diversification as opposed to homogenisation possible in terms of species traits.
How, I hear you ask, does this mean that biology teachers suck?
Because they still teach children that animals can be classified like this:
Invertebrates and Vertebrates.
which is a linnaean (i.e. pre-darwinian) classification, and while Linnaeas (may his excellent remains rest in peace)... A hagfish - which is an invertebrate - is nevertheless much more closely related to the visually very similar lamprey, a vertebrate, than it is to other invertebrates such as insects.
This is rather more serious than the main point I am addressing here, so it takes all my self control not to write 2000 words on how awful this is. I may yet fail.
So invertebrates is what we call a Paraphyletic group - it does not include all descendents of its most recent common ancestor, and - as a result - is a descriptive word but not an accurate biological group.
This is important. Remember it.
The next awful thing that is done by biology teachers is teaching us that vertebrates are classifies into five groups:
Fish Amphibians Reptiles Birds Mammals.
(some go the extra mile in misinformation and call these Classes).
In fact, modern fish fall into 4 classes:
Chondrichthys
Actinopterygii
and
Sarcopterygii
Petromyzontiformes (actually an order with no fixed class)
(a whole bunch more extinct fish are found in the classes Placodermi, Acanthodii, Conodont, Pteraspidomorphi, Thelodonti, Anaspida, Galesaspida.
And finally, Leptocardii and Myxiini are two extant (i.e. living species exist) classes which are also sometimes treated as fish... and they're both invertebrates (Leptocardii are lancets... little fishlike things of wierdness, Myxini are hagfish, which are jawless invertebrates which are surprisingly difficult to tell apart from lampreys except that lampreys have a spine)
Going back to the four modern "Classes":
Chondrichtyes are "cartilaginous fish", whose bones are made of springy cartilage (the chewy white stuff at the joints on chicken drumsticks). Sharks and rays are the prominent modern examples.
Actinopterygii and Sarcopterygii both fall within the "Osteichthyes" (along with the extinct spiny sharks, Acanthodii), a group which is typically referred to as bony fish.
The Actinopterygii are quite simply referred to as the ray-finned fish, and are typically considered the largest class of vertebrates. They include most of the animals you would think of as fish in your day-to-day life, from cod to
The Sarcopterygii are the lobe-finned fish, as unlike the silly fins supported by fragile (well...) rays in the Actinopterygii, these guys have bones in their fins. Traditionally, eight modern species are included here - comprising the living fossil groups coelocanths and lungfish.
(it now gets complicated)
The point is that One class is not equal to another. The term has its history in the early days of taxonomy, before many of the finer details of vertebrate evolution were understood, and so Aves is a class within Reptilia.
This is relevent to our point only in that all four classes of land vertebrate belong within the class Sarcopterygii.
Do you remember the word paraphyletic?
It means that a grouping does not include all descendents of the most recent common ancestor. The most recent common ancestor for Sarcopterygii is quite vastly different from the modern groups, because the Lungfish and Coelocanths are not particularly closely related, and in fact, the Lungfish group with an interesting and diverse group called the Tetropods before they group with the Coelocanths.
The Tetrapods include the four classes of land vertebrate that we talked about earlier.
And it's nestled within the Sarcopterygii.
Which are universally acknowledged as being fish.
Amusingly enough, this takes the Sarcopterygii from being the smallest class of vertebrate (8 members), to be the largest - including almost 20,000 known reptile species (including birds), over 7000 amphibian species and nearly 5500 mammals, it totals at over 32,000 known species.
One of which is of course the afore-mentioned blue whale.
At this point, we have to talk about English for a bit.
Specifically, how a word can have one meaning in descriptive English and another altogether when treated as a biological group..
As we have already established, Fish as a biological group includes all descendents of its earliest common ancestor... which is to say, every single vertebrate (although some sources are uncertain on lampreys).
In English, however, a fish is diagnosed on aspects of its morphology - typically by having both gills and a spine.
As a preliminary examination of an adult* blue-whale will discover, it has no gills.
So if an English teacher wants to know the largest fish in the sea, the right answer could still be the whale shark.
But if a biology teacher asks, within the context of a biology lesson, the correct answer is the blue whale.
If you intend to put things right, ask a biology teacher whether they are taking into account the last 150 years of evolutionary biology. If they look puzzled and say yes, tell them that as a sarcopterygian, the blue whale is indisputably the largest fish in the sea, and indeed the largest fish that is ever known to have lived, although a possibility remains that larger fish belonging to the clade Saurischia existed in the cretaceous period but fossils either do not exist or have not yet been found.
And to all the people I have loathed for saying that the largest fish in the sea is a blue whale over the years, I am sorry.
You were right.
Although only because you were too ignorant to have thought about basic biology.
So I rescind my apology.
Smivel
*However, all mammals do have gills as embryos. Which is one argument that even in plain english, the largest fish would have to be the blue whale.
PS - addressing the title, I am a human, humans are Mammals, Mammals are Tetrapods, Tetrapods are Sarcopterygians, Sarcopterygians are Fish. Ergo I am a fish.
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