You're viewing a single thread.
I feel like jellyfish does a pretty good job of living up to it's name.
Since there isn't really any agreed upon scientific definition what "a fish" is, it's pretty much a perfect name
there isn’t really any agreed upon definition what “a fish” is,
are you sure?
There is no sensible phylogenetic definition of "fish" which includes both trout and sharks but not humans.
They respire using gills.
They respire using gills.
See here for a list of "fish" which respire using gills: https://en.wikipedia.org/wiki/Gill#Amphibians
I don't see humans on that list.
Are sharks fish? Sharks are fish. They live in water, and use their gills to filter oxygen from the water.
Seems pretty easy to me. Even lungfish have gills.
Axolotl are fish
Frogs are fish
Do frogs have gills? The tadpole stage of frogs might be fish, but adult frogs aren't fish.
But, whether or not you want to consider axolotl and frogs fish, "gills" is a neat line that separates humans from trout and sharks.
Sure but what the OP was saying is that these common definitions of fish are paraphyletic. In order to make a monophyletic group including everything we call fish, we'd have to include humans, birds, lizards, etc. And going by the water-and-gills definition, this group would include things we tend not to call fish like crabs, amphibians, sea slugs, some insects... Not to mention that gills have evolved multiple times. And something like a frog being not a fish but it's larvae being fish doesn't make sense for cladistics.
separates humans from trout
I'm a little bit curious about why you specifically selected humans to be differentiated from fish
Because:
There is no sensible phylogenetic definition of “fish” which includes both trout and sharks but not humans.
Gills.
I'll be just as terse
phylogenetic
I admit I don't really know much about that. But Wikipedia says:
In biology, phylogenetics (/ˌfaɪloʊdʒəˈnɛtɪks, -lə-/)[1][2][3] is the study of the evolutionary history and relationships among or within groups of organisms. These relationships are determined by phylogenetic inference methods that focus on observed heritable traits, such as DNA sequences, protein amino acid sequences, or morphology.
Where morphology is:
Morphology is a branch of biology dealing with the study of the form and structure of organisms and their specific structural features.[1]
This includes aspects of the outward appearance (shape, structure, colour, pattern, size), i.e. external morphology (or eidonomy), as well as the form and structure of the internal parts like bones and organs
It sure seems to me like that should cover gills.