Quote Originally Posted by Honest Tiefling View Post
Perhaps to make it easier for yourself, limit the number of animals in the system? I mean, if its Archaic, chances are no one can hop onto a plane and see exotic animals or take a trip to the zoo. If we assume a North European biome for the sake of an example, elephants, monkeys and a few other outliers (fossa, binturogs, platypi, etc.) can be ignored.
Relevant to this: Aristotle only classified around 500 vertebrate animals, and he was operating in a Mediterranean environment with exposure to a relatively large number of different climates compared to many other persons in the ancient world.

An archaic taxonomy simply isn't going to function at the species level except in the case of a very small number of extremely prominent examples - large bodied mammals mostly, certain notable birds, food plants - and most languages won't even have words for descriptions below the genus or even family level. Shrews, for example, are a family with high diversity. France alone hosts ten species. However, in an archaic scenario, people who probably consider all shrews to be the same type of animals, differentiated only by size if at all.

Aristotle's taxonomic system - which is really the only formal archaic taxonomy there is, non-western societies don't seem to have developed this field in detail - was based on what were actually pretty good observations of morphological traits given the tools available to him. No microscopes, poor equipment for dissections, and no collection libraries for comparisons of large numbers of organisms at once (the Linnaean system was developed using plants, and relatively modern herbarium techniques were developed prior to its creation).

As a result, I'd suggest that you shouldn't worry about phyla outside of Chordates for your system really at all. Those can be completely ad hoc. What you want is a system that can differentiate major groups of fish, break fish from tetrapods, differentiate major tetrapod groups, and then meaningfully differentiate birds and mammals to somewhere around the superorder level.

A big factor here is how many extinct and/or purely fantastical organisms are wandering around your setting. Take just 'fish' for example. Modern groups gets you hagfish, lampreys, Chondrichthyes, Actinopterygii, and Sarcopterygii. Extinct groups adds in Placodermi, Acanthodii, a whole mess of 'jawless fish' groups like the Osteostraci, and even Conodonts. Tetrapods is worse and extinct mammals worse still.