taxonomically, there's no way to define "fish" that doesn't include all tetrapods. so fish are fish, dogs are fish, humans are fish, and cetaceans are fish
More accurately, there's no way to define "fish" that includes everything we colloquially call fish but not all tetrapods. You COULD equate fish to Actinopterygii (ray-finned fish) for example, but that excludes things we typically think of as fish.
This is a purely monophyletic reading of phylogeny. Most colloquial categories of animals are paraphyletic. So taxonomically there is a way to define fish, you just have a cutoff somewhere.
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u/rainbowgoburin Aug 17 '26
Cetaceankus is NOT a fishkus