E621 does not use accurate taxonomy. This is intentional. While the argument can be made that accurate taxonomy could be a better systems, that's not what I'm trying to get at with this topic.
Instead, I just wanted to create a broad topic wherein any deviations from understood taxonomy could be discussed, so that we have a record of all the ways that we knowingly deviate from taxonomic classification. The idea being that future discussions of species implications and aliases can be easily checked against previous discussions...
Group 1: Implications we know are wrong and keep anyway.
Mosasaurus -> Dinosaur
Ichtyosaurus -> Dinosaur
Pliesiosaurus -> Dinosaur
Liopleurodon -> Dinosaur
Pteranodon -> Dinosaur
Group 2: Implications we know are right but ignore.
Human -> Ape
Ape -> Monkey (yes, really)
Bird -> Dinosaur
Snake -> Lizard
Dog -> Wolf
Dolphin -> Whale
Group 3: Mythological and Furry-Specific Supergroups.
Avian
Includes birds and mythological feathered creatures.
Scalie
Includes reptiles, amphibians (?) scaled dragons, and scaled dinosaurs.
Pokemon
Pokemon are not given species-level categorizations.
Group 4: Things we don't want to deal with.
Reptile
Reptile as a classification is a huge mess that we probably don't want to get into.
Fish
See above.
Ungulate
Aliased to mammal - would be useful as a classification for hooved animals, except that it would also include whales.
Group 5: Things I'm not sure on.
Panther -> Feline
These are sister clades - Panthers are not felines. The group which includes both panthers and felines is Felidae, members of which are called felids.
Saber-Toothed_Cat -> Feline
As above, they are felids, but not felines.
Tick -> Arachnid
Ticks are arachnids, though this implication doesn't exist. An oversight, perhaps? Or just too small to bother with.
Mammoth -> Mammal
As above, no implications for this. Might be worth considering. Mammoths and elephants both belong to proboscidea, but ain't nobody ever gunna search that.
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Again, it seemed useful to categorize all this together. If you've got anything to add, or any other oddities to question, I'll try to keep this updated.
Updated by Aegis29