"Reptile house? What's that?"
In Real Life, there are many species that theorists have speculated can evolve over time into something of comparable sapience and intelligence to humans. Not all of them are mammals; among the non-mammalian species considered to have similar intelligence to humans are crows, parrots and cephalopods.
In fiction though, many works exist in universes full of nothing but humanoid animals or humans interacting with humanoid animals. Many of these works feature humanoid animals of many types, but often focus exclusively on mammals. More specifically land-based mammals, as rarely are exclusively aquatic mammals, such as dolphins or manatees, ever included.
This trope can occur for many reasons. The designers might find humanoid reptiles or birds too weird looking or hard to draw. They might be under the belief that only mammals have the potential or intelligence to become sapient. Or possibly, they also being mammals, just prefer mammalian animals or are more familiar with how mammals work. Another reason for this might be a way to avert Carnivore Confusion. Instead of having Vegetarian Carnivores or having characters eat meat without explanation as to where it's from, instead it's implied (or outright shown) that they eat non-anthropomorphic birds or reptiles.
This trope is sometimes subverted by throwing a token bird or reptile into the mix.
See also No Cartoon Fish. Compare Furry Confusion, where anthropomorphic and non-anthropomorphic animals coexist without any taxonomical distinction.
Examples:
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Advertising
- The Coco Pops mascot lives in a world where there are animals populating jungles and cities. The animals we see are mostly mammals, with some birds and reptiles.
Anime & Manga
- Downplayed in Aggretsuko: While most of the characters are mammals, there are several bird characters (at least two secretary birds, an ostrich, and, at least in the Netflix version, an owl), a reptile in the form of a Komodo dragon, and an amphibian in the form of an axolotl. It would seem that, given that one episode of the TBS series shows a plate of squid-based food, marine invertebrates at the very least aren't sapient, but given that the same episode also shows a plate of poultry of some kind, it isn't exactly clear...
- Most of the major beastmen in BNA: Brand New Animal are mammals (Michiru is a tanuki, Shirou is a wolf, Marie is a mink, etc.), with a few birds and reptiles as supporting characters.
- Dragon Ball (especially in the early chapters) features Beast Men that are mostly mammals with the occasional reptile (such as a crocodile or dinosaur) with some playing major roles such as Oolong. Birds, amphibians, fish, and invertebrates are no to been seen (on Earth that is).
- Maple Town features Funny Animal rabbits, bears, dogs, and foxes but no fish or birds and reptiles only appear as background characters in Palm Town.
- In One Piece, the Minkmen are all Beast Men who are based on only mammals. All of them, including the ones based on herbivore mammals, can and do eat meat (usually that of reptilians or fishes; hippos are also included in their diet, weirdly).
- In Seton Academy: Join the Pack!, every student shown is a mammal, whether a Little Bit Beastly girl or an upright realistic-looking male. However, the teachers are dinosaurs (well, most of them are dinosaurs with one pterosaur and one spider-monkey), while the headmaster is a prehistoric anthropod called an Anomalocaris.
Art
- Downplayed in Beast Fables. There are werebeasts for all of the major land animal groups (tetrapods and certain arthropods), but mammals are the most dominant clade.
Comic Books
- Albedo: Erma Felna EDF, just like Zootopia, features mostly exclusively mammals, but, unlike the Disney film, it does feature anthro birds as well, through they look more like bigger versions of their non-sentient ancestors. Also, and very unlike Zootopia, the only non-sentient fauna that appears are fish and crustaceans exclusively. There's no other alien fauna, not even insects like flies, fleas, or cockroaches. Likewise, and by Word of God, any other mammal that requires special habitats just for survive, like dolphins, orcas and the like, doesn't appear either. And needless to say, primates are nonexistent, due to their relationship with the Creators, aka the human race.
- Averted in Maus; the central characters are depicted as mice and cats, but the animals depicted also include frogs, fish and moths.
Films — Animation
- In Cat City, only cats, mice, rats and vampire bats are portrayed as anthropomorphic, whereas caimans, snakes and parrots are Nearly Normal Animals (although the parrot can talk). The sequel throws an anthropomorphic badger into the mix except it doesn't, the badger in question is a mouse in disguise, but also shows a non-anthropomorphic leopard, sloth and buffaloes.
- Inverted in The Good Dinosaur, where dinosaurs (at least non-avian ones) and pterosaurs are sapient Partially Civilized Animals, but mammals (including humans) and birds are Nearly Normal Animals.
- Subverted by Robin Hood (1973); the majority of the cast are mammals (including foxes, lions, bears, wolves, rabbits, mice, badgers...), but there are a few token non-mammals, like Sir Hiss and Lady Cluck (who are, respectively, a snake and a hen.)
- Subverted in Rock Dog. Initially it seems to take place in one of these. It features mammals such as dogs, foxes, goats, cats, sheep, and wolves. However, reptiles such as crocodiles also show up.
- Zootopia (2016): The titular city is populated by evolved mammals set in a world where humans never existed. Therefore, animal species domesticated by humans (such as domestic dogs) rarely appear, although there are a handful of exceptions (for example: domestic sheep, horses, and pigs exist). Word of God mentioned that primates were not shown in the movie because they appeared too human-like (but didn't deny their existence, and concept art for the movie features a bushbaby), and has hinted, but not confirmed, that a city inhabited by reptiles and birds may exist. The only non-mammals seen at all are the non-anthropomorphic houseflies flying around Yax’s head, a fish restaurant, and the implications of another restaurant called Bug Burger. Subverted in Zootopia 2, which shows that anthropomorphic reptiles exist in this universe, but those reptiles who live in Zootopia were forced into hiding by mammals who don't take kindly to them, with Nick even saying at one point that "no snake has set foot in Zootopia in forever." There is a hint that anthropomorphic birds exist as well.
Literature
- Barsk: The Elephants' Graveyard takes place in a Milky Way populated by over eighty species of anthropomorphic mammals, and only mammals. This turns out to be because they were all genetically engineered by humans to be capable of language, and only mammals had compatible physiology.
- The Number Two Feline Detective Agency series is set in an all-cat world.
- Rainbow Bridge: The poem mostly reflects on mammalian pets, like dogs and cats. Presumably there's places for birds, fish, and other animals before the Rainbow Bridge, but it isn't discussed in the poem.
- Spellsinger: Downplayed, as there are sentient birds, turtles, frogs, and insects, but mammals are the overwhelmingly most common sapient animals in the setting.
- Tasakeru is somewhat like a Darker and Edgier take on Zootopia above. Humans never existed, and selected mammal species have evolved to become anthropomorphic "sentients". Unlike Zootopia, the sentients are shown to have domesticated animals such as chickens, goats, sheep, and pigboars.
Tabletop Games
- The Delver's Guide to Beast World: While there are an assortment of non-sapient animals throughout the Beast World, its native inhabitants are all based on various species of mammals, who were uplifted, evolved and manifest their own societies over the ensuing millennium-and-change. While sapient non-mammals exist, none of them are native:
- The brethren (humans) come from a world where the laws of reality are breaking down, and while they started a war over the land and slaughtered many "monsters", the lion's share of them (proverbially speaking) ceased hostilities once they realized that the "monsters" were just as intelligent as compassionate as they were. Even the Ghost God - the amalgamation of humanity's former pantheon - emigrated with them to escape the ensuing chaos.
- The dragons are young emigrants from a world where arcana and nature alike were tamed by powerful magical forces, driving the divinity to mind-numbing boredom and convincing them to observe life elsewhere; the divinely-induced fertility crisis that followed led to them making kobolds as a substitute and, when that failed, eventually emigrated to the Beast World as a last resort. This led to interesting results when some of the kobolds that followed started taking on lives of their own...
- Ironclaw started out with mammals and birds anthropomorphized while reptiles (some resembling dinosaurs) as wildlife and beasts of burden. However, Jadeclaw, which is established to take place on the same planet, threw in anthropomorphized reptiles, amphibians, and even arthropods.
Video Games
- The two races in the Little Tail Bronx series are anthropomorphic dogs and cats. Per supplementary materials, this is a justified case alongside the series' Earth All Along backstory: Yurlungur, an Artificial Intelligence born from the Juno entities responsible for the world's recreation, had interacted with a team of researchers who had chosen to raise several dogs and cats for their mental health. Yurlungur therefore chose dogs and cats as humanity's successors due to both their adaptability to different environments and out of her perception that they were partners to humanity.
- Small Saga takes place in the Mouse World kingdom of Rodentia, which is under the streets of London. There are three or four Lizard Folk around, and friendly talking pigeons transport rodents in the air in baskets, but the reptiles are rare and there are no birds in the rodents' enclosed cities. It's probably too cold for a lot of reptiles, and since the birds are all pretty normal-shaped and don't have Feather Fingers they're more comfortable outside.
- A majority of the Sonic the Hedgehog cast are mammals, though Team Chaotix, which consists of two reptiles and one insect, and the Babylon Rogues, a team of birds, are thrown in.
- Inverted in Splatoon: almost everyone is a marine invertebrate or a fish, some of whom can transform into human-like forms. The only mammal is Judd (and his clone), a cat who's the Last of His Kind. Splatoon 3 reveals that there's another one; Mr. Grizz is a grizzly bear, and his plan is to turn Earth into a World of Mammals once more.
Visual Novels
- In The Hayseed Knight, every character but one is either a deer, a gazelle, or a wolf. Said exception is a sentient tree, and although others of his kind exist, they tend to be non-communicative and overtly hostile to the mammals.
Web Animation
- All the main characters in Happy Tree Friends are mammals, mostly woodland creatures. The show only has ever had a few non-mammalian characters with Sneaky the chameleon and some members of Splendid's Super Squad, who only ever appear once in the Ka-Pow spin-off. The Ant Family, while having some anthropomorphic qualities, otherwise act like natural bugs and are often preyed upon by Sniffles.
Webcomics
- AGENCY is a Massive Multiplayer Crossover webcomic where most of the characters are Funny Animal mammals from various pre-existing works.
- Precocious exaggerates this trope, by having only canines and felines be civilized. This was done as a means of preventing Furry Confusion.
Western Animation
- Inverted in Amphibia, where the only animals that are sapient and anthropomorphic are amphibians such as frogs, toads and newts. The few mammals that appear other than our Token Human lead (such as hedgehogs and weasels) are non-sapient and often monstrous.
- Every character in Archibald the Koala is an anthropomorphic koala or badger, with no other species to be seen.
- Downplayed in Arthur. Almost all the characters are mammals, but non-mammals very occasionally show up. Most often, Funny Animal reptiles and birds appear in the background or as gags.
- Carl the Collector: Fuzzy Town plays this almost straight, the only noticeable exceptions being Mr Price, a lizard, in the Halloween special and the punk rock turtle band.
- Dog City: Most characters in both the puppet and animated worlds are dogs, with the occasional cat. One episode reveals that the Show Within the Show has a rival series about anthropomorphic rabbits, but it's not made clear if anthro rabbits are "real" in Eliot's world, or if this is the equivalent of a Funny Animal cartoon within the story.
- Subverted in both versions of DuckTales. Most of the world's populace are birds as well as mammals. Anthropomorphic reptiles, amphibians, and invertebrates are shown to exist, although the only ones seen are supernatural beings.
- Elinor Wonders Why: Animal Town is filled with all manor of anthropomorphic mammals; from rabbits, to rodents, to bats, to ungulates, and marsupials. Birds, reptiles, fish and invertebrates all appear as non-sapient.
- Llama Llama is populated entirely by mammals, with the added caveat that the main cast are all herbivores that would normally travel in herds, i.e. llamas, sheep, giraffe, gnus, etc. Minor/background characters have included other types of mammals, such as dogs, cats, chipmunks and even hippos. The only non-mammal character that plays any role is a pet duck that is owned by Llama Llama's grandparents.
- Inverted in SpongeBob SquarePants. Almost all of the characters are invertebrates or fish, with the only recurring mammal characters being Sandy (a squirrel in a diving suit) and Pearl (a whale). Other whales have appeared from time to time as background characters, the episode "Sun Bleached" has a one-shot seal character, and Kenny the Cat appears in his eponymous episode.
- All of the characters in Timothy Goes to School are mammals, while other animals seem to be the same as in real life. For example, Nora (a mouse) has a pet lizard.