At least, that is as far as I understand the meaning of the words, and I could be wrong. Nevetheless, it got me thinking.
I was thinking that rats and mice are clearly different enough that they need to have different names, and that kamo and ahiru, while different species, clearly are both ducks (in fact, most domestic ducks are bred from mallards) . But... if we go to Wikipedia and check, then the result is that rats and mice are very closely related (same family, but different genera)
[When I was working in New York I often went to Peebler Point in Central Park. One year a lone domestic duck was trying to hang out with a group of mallards, but that didn't go so well. It was clearly the odd one out, being much larger and white, and the mallards were not very welcoming, though also not directly chasing the outsider away.]
Then I was asked why alligators and crocodiles have different names. (I should note that I am not a zoologist, so all information I have to share is amenable to correction.) My first thought was that they are not just different species, but probably different families of crocodilians, and I further had the hunch that most common names of animal groups in English describe families. But it turns out that there is a lot of variation. Incidentally, alligators belong to one genus, while all crocodiles is a family. The list below includes some of the most common names of animal groups that I could think of, and as can be seen, the names cover genera through superorders. While surprised at this range, I wasn't exactly expecting that the old names for the animals wold confirm to taxonomic nomenclature. This inconsistency probably has to do with
- the closeness and utility of the animals to humans,
- where we draw the lines between taxonomic clades, which partly has something to do with morphology and species diversity, and
- (least interesting) my particular choice of what I consider "common animal groups."
Unless noted otherwise, the groups are Monophyletic, meaning that all the species in the group share a common ancestor that they do not share with species that does not go by the listed name (e.g. all ants species are members of the family Formicidae, and all member of the Formicidae are ants).
Pig - Genus (Sus)
Mouse - Genus (Mus)
Rat - Genus (Rattus)
Alligator - Genus (Alligator)
Crocodile - Family (Crocodylidae)
Horse - Family (Equidae)
Dog - Family (Canidae)
Cat - Family (Felidae)
Duck- Family (Anatidae1)
Eagle - Family (Accipitridae)
Bear - Family (Ursidae)
Ant - Family (Formicidae)
Ape - Superfamily (Hominoidea)
Bee - Superfamily (Apoidea)
Monkey2 - Superfamily (Cercopithecoidea)
Shrimp - Infraorder (Caridea)
Dinosaur - Suborder (Dinosauria)
Snake - Suborder (Serpentes)
Parrot - Order (Psittaciformes)
Bat - Order (Chiroptera)
Fly - Order (Diptera)
Whale3 - Order (Cetacea)
Shark - Superorder (Selachimorpha)
1 Anatidae is paraphyletic (i.e. not monophyletic) and includes swans and geese.
2 "Monkey" covers both old world (superfamily Cercopithecoidea) and new world (pavorder Platyrrhini) monkeys, and is a paraphyletic group.
3 Includes dolphins and porpoises.
Bonus fact: Here's a mallard without webbed feet. It hates water. I can imagine why.