It's Ofishal: Humans Are Technically Fish

When the chips are down you've got more in common with dinner than you think.

Pitted stingray at Osaka Aquarium © Poppy Simon

You might have heard that birds are technically dinosaurs, but did you know we're all technically fish?

Just like birds are directly evolved from dinosaurs, all tetrapods (mammals, reptiles, amphibians and birds) are directly descended from a particular type of fish. Fish are broadly divided into two groups - cartilaginous fish (sharks and rays, or Chondrichthyes) and bony fish (a.k.a. normal fish). Within the bony fish though, there's another division that turns out to be quite relevant to us.

The bony fish are divided into ray-finned and lobe-finned fish. Ray-finned fish (catchy scientific name Actinopterygii) are again what you might think of as normal fish, from tuna to trout, and are so called because their fins consist of webs of skin supported by bony spines called rays. Lobe-finned fish (Sarcopterygii) on the other hand have fleshy lobes - tasty. There are 8 species of lobe-finned fish that are what you would think of as fish (six species of lungfish and two species of coelacanth*), but also -drum roll - all tetrapods are directly descended from the lobe-finned fish.

Whale shark at Osaka Aquarium © Poppy Simon

Going back to our original two groups of bony fish and cartilaginous fish, this means that humans, like the diver below, are more closely related to (ray-finned) fish than sharks are. Yep, we have more in common with a fish dinner than a shark or ray does.

To put it another way, despite their apparent similarity, whales and dolphins (ie. mammals) are more closely related to, say, a seahorse than sharks. This is a pretty great example of parallel evolution, where two unrelated species (or groups of species, ie. whales/dolphins, and sharks) develop similar characteristics because of their shared environment.

Human diver at Osaka Aquarium © Poppy Simon

This post was inspired by a recent BBC Earth competition to find their next presenter - the application consisted of filming a 60 second video explaining your favourite science or nature fact. I was struggling for a little while to think of something but was reminded of my favourite shark fact while at Osaka Aquarium over the summer, and it seemed a shame not to share it here!

*Coelacanths are pretty cool: 'living fossils' thought to be extinct until they were rediscovered in 1938, impressive given that they can grow to more than 2m long...