Which buddy Pokemon can ride on your shoulder?

Question

Version 0.37 of Pokemon Go introduced the buddy system, which allows you to designate one of your Pokemon as a "buddy", allowing you to earn candy corresponding to that Pokemon as you walk.

Your designated buddy Pokemon appears with your avatar in one of the in-game menus. However, the position of these Pokemon as they appear with your avatar depends on the Pokemon's size - some smaller Pokemon even sit on your avatar's shoulder! My question is: of the Pokemon currently available in Pokemon Go, which ones will sit on your shoulder? (And what positions do the other Pokemon appear in, while we're at it?)

Answer 1

Here's a list by position:

Shoulder: Caterpie, Weedle, Pidgey, Spearow, Pikachu*, Eevee, Plusle, Minun

Stands by your side: Bulbasaur, Charmander, Charmeleon, Squirtle, Wartortle, Metapod, Kakuna, Rattata, Raticate, Ekans, Raichu, Sandshrew, Sandslash, Nidoran Female, Nidorina, Nidoran Male, Nidorino, Clefairy, Vulpix, Jigglypuff, Oddish, Gloom, Paras, Parasect, Venonat, Diglett, Meowth, Persian, Psyduck, Mankey, Growlithe, Poliwag, Abra, Machop, Bellsprout, Tentacool, Geodude, Ponyta, Slowpoke, Farfetchd, Doduo, Seel, Dewgong, Grimer, Shellder, Krabby, Voltorb, Exeggcute, Cubone, Marowak, Lickitung, Tangela, Horsea, Goldeen, Staryu, Mr. Mime, Electabuzz, Magikarp, Ditto, Vaporeon, Jolteon, Flareon, Omanyte, Kabuto, Dratini, Mew**

Stands behind you: Ivysaur, Venusaur, Charizard, Blastoise, Arbok, Nidoqueen, Nidoking, Clefable, Ninetales, Wigglytuff, Vileplume, Dugtrio, Golduck, Primeape, Arcanine, Poliwhirl, Poliwrath, Kadabra, Alakazam, Machoke, Machamp, Weepinbell, Victreebel, Tentacruel, Graveler, Golem, Rapidash, Slowbro, Magneton, Dodrio, Muk, Cloyster, Gengar, Onix, Drowzee, Hypno, Kingler, Electrode, Exeggutor, Hitmonlee, Hitmonchan, Koffing, Weezing, Rhyhorn, Rhydon, Chansey, Kangaskhan, Seadra, Seaking, Starmie, Scyther, Jynx, Magmar, Pinsir, Tauros, Gyarados, Lapras, Porygon, Omastar, Kabutops, Aerodactyl, Snorlax, Moltres**, Dragonair, Dragonite, Mewtwo**

Flies behind you: Butterfree, Beedrill, Pidgeotto, Pidgeot, Fearow, Zubat, Golbat, Venomoth, Magnemite, Gastly, Haunter, Articuno**, Zapdos**

*Pikachu is a special case: it will stand by your side when first selected as your buddy, but will move to your shoulder once you've received 10 candies from it.

**These Pokemon are not currently available: information for these Pokemon is based off of datamining the app.

Source