The Pokémon Taxonomy Project

Definition

Ancestrally arboreal Pokemon that begin life as small larvae with six appendages and undergo a dramatic change before adulthood, at which point they gain round or triangle-shaped, pigmented wings, a body consisting of two or three segments, and zero to six appendages.

Common Traits: Many Viridopterans exhibit compound eyes at some stage in development. Many also have scaled bodies made from pressed hairs, and many exhibit hair in addition to these scales.

Name: "Wings of Viridian", named for the Viridian Forest of the Kanto region. Viridian Forest is a popular site for watching Butterfree and is heavily associated with a key member of the family. These species also show traits clearly related to arboreal ancestry.

Reasoning

Real-life bugs and moths have fairly similar traits and are accepted to be in the same superfamily. The classification here is extremely similar to the classification lepidoptera (I even stole some of the name). Many lepidopterans (such as Butterfree and Venonat) specifically describe scales in their Pokedex entries, which I can assume to be analogous to those of lepidopterans in real life.

Explanations

Caterpie, Scatterbug, Wurmple: These closely fit the definition described above. Caterpie and Scatterbug are close enough in their biologies to potentially belong to the same genus (both beginning life without compound eyes and ending with compound eyes, their larvae having three pairs of legs, their adult forms having two round wings with colorful patterns and four frong-facing appendages each, both having dust they emit for survival, and so on). Wurmple also fits this definition, but Beautifly and Dustox are dissimilar enough from Butterfree and Vivillon to constitute somewhat of a seperation taxonomically. Beautifly's proboscus and general body proportion are different, and Dustox is completely distinct in terms of body shape while continuing to have the other features listed.

Venonat: Venonat does not chrysalize, but it does still undergo a major transformation in evolution- going from a furry, arboreal form to one capable of flight. It shares hair and scales with other members of the family. Strangely, it has compound eyes in its adolescence that seem to fuse when it enters adulthood. Venomoth is likely closely related to Butterfree, as both use similar poisonous powders to help trap prey. However, because Venonat do not chrysalize- a major part of development for the above species- I do not think they are as close as Caterpie and Scatterbug.

Snom and Larvesta: Snom is clearly intended to be a larval moth, and Larvesta is literally called such. Neither chrysalizes in evolution, but both still undergo massive changes when maturing (and Larvesta, as @orsan1070 pointed out, does form a chrysalis according to its Pokedex entry and merely doesn't have a seperate evolution stage for it). Frosmoth, however, has fewer than usual front-facing appendages, while Volcarona has an unusual number of wings among its peers. Even still, I feel comfortable keeping the two in this group because they have all other necessary characteristics. They do not seem particularly closely related to one another, though, as their body structures show significant difference.

Edge Cases

Burmy: Part of a group of Pokemon I have no choice but to classify as 'floaters', Burmy and Wormadan present a strange conondrum in that their larval stages can fly without wings. Am I assume this relates them more closely to a line line Pineco? Or should I assume these are merely chrysalises that only metamorphose in male Burmies? I lean toward the latter, as none of Burmy nor Wormadan's entries indicate the Pokemon floats as typically seen in its depictions.

Surskit: It does undergo metamorphosis. Masquerain does have triangle-shaped wings, and it does have a two-segmented body. However, the movement of its wings is unlike other Viridopterans in that they flap perpendicular to its body rather than parallel, similar to a Yanma's. Surskit is also does not fit any other Veridopteran bodytype, which leads me to indicate it is not part of this family.

Cutiefly: Doesn't metamorphose. May revisit later.

who set this up. why has nobody done research over this. i thought there were state of the art fossil labs around the world. like. didn't the goofs out in kalos just have a big breakthrough on mega evolution or something? how are we going through all of that without having proper classifications for the creatures that literally allow our society to function?

my larvesta is trying to get me to calm down. more people are paying attention to this silly little blog than initially anticipated. and it is important not to get blacklisted from those same institutes for being unprofessional. (i'm not unprofessional. im just late and mad nobody has done this better before)

wait i was talking about monster egg groups RIGHT okay

careful research about movement patterns reveals, firstly, that the monster egg group has a huge variety in types of locomotion. this includes creatures that are bipedal, quadrupedal, aquatic, and even one that slithers- although I am unsure as to Drampa's true role in this but i think its important.

there also seem to be some interesting examples of development in bony head crests and coverings, which comprise a significant portion of this egg group. this includes archaic lines like tyrunt and cranidos, as well as modern examples such as helioptile and axew.

both locomotion as well as the head crests are features shared amongst different egg groups. monster and field have some degree of overlap, so this might be a lead as to where to start. for now, I think I will be temporarily splitting the different monster egg groups into taxa based on locomotion. that will include monstrous bipeds, quadrupeds, aquatic pokemon, and drampa.

types appear to have less impact on relation than other factors and will not be considered extensively. alolan vulpix and kantonian vulpix are obviously closely related, but they do not share types. meanwhile, grapploct and gallade are both fighting types, but their native environments, body structures, and movepools are completely different. as such, type appears to relate more to a pokemon's behaviors and environment than to its evolutionary history.

2. egg group will hold more weight than type, but not extensively. gallade and grapploct are both in the human-like egg group despite varying wildly in structure (as discussed above). relation is implied by the ability for these species of pokemon to interbreed, but the games allow wildly different pokemon to breed with one another and produce fertile offspring. I feel safe assuming that these same creatures capable of spitting fire and defying conservation of mass when dynamaxing can use similar magical powers to breed.

3. evolutionary lines will be assumed to be the same species unless something weird is going on (like shelmet/karrablast seeming to have some kind of symbiotic relation... tbd). different evolutions on a line will be assumed to be life stages of the same species. I know the anime specifies that evolution is not equal to age, but these pokemon are capable of metamorphizing into one another given 'experience', which seems to usually equate to age. Either way, 'experience' is weird and a subjective way to measure stuff, so I am just going to assume that all pokemon of a line are innately related. I will be referring to lines by the first pokemon in that line, unless that pokemon is a baby.

4. baby pokemon will be regarded as sharing taxa with their adult forms for the above reasons. baby pokemon tend to be listed in different egg groups than adults in most games because of breeding shenanigans. I'm going to treat them as normal prevolutions. However, for lines that have baby pokemon, I will not be labelling them with the baby as the first evolution for ease of ctrl-F when I'm looking through various pokedexes (ex. Snorlax will include the line of Snorlax, which is Munchlax and Snorlax).

5. we have a universal common ancestor, which is mew.

6. I will assume legendaries are not typically part of taxa unless otherwise specified, as many of them were created directly by arceus instead of evolving. one may try to argue that the existence of pokemon made directly by arceus canonizes a sort of creationist view of the pokemon universe, but I think that's dumb and stupid and bad, so I won't be acknowledging it. also convergent and divergent evolution are canon in pokemon, as well as fossil pokemon.

7. certain legendaries without lore on their creation will be classified along with other pokemon (the legendary birds, manaphy, phione, the lati twins, etc). if a pokemon does have lore as to their evolution, they will also be listed with proper taxa (ex. genesect).

8. i have no idea what to do with object pokemon and they scare me. i'm generally going to assume pokemon like sinistea, rotom, etc refer to the ghost possessing whatever object rather than including the object itself as a shell or something based on dex entries.