When it comes to World Building, writers often want to populate their world with a fantastic fauna different from our own. However, at the same time they want this fauna to be somewhat believable and/or familiar to the viewers. One way to achieve this is to make some of the fantasy species the exact counterparts of a real-world animal. Thus, we end up with things like giant insects flocking like pigeons, giant reptiles hunting in packs and howling like wolves, or tentacled creatures swinging from trees like monkeys. In a sense, each species acts like an Expy or a Suspiciously Similar Substitute of a different species.
The trope has two main variants. In one version, a number of fantasy/alien/prehistoric species are presented as counterparts to mundane, modern species. In the other version, the animals are mundane species, but clearly fill the role of other, more familiar species - for example, an underwater setting where fish and other sea creatures act like mammals and birds, a Mouse World where insects and other invertebrates are counterparts to larger animals, or a World of Mammals where there are other classes of animals replacing non-sapient mammals. A World of Funny Animals setting can use this trope to avoid Furry Confusion - if certain species are anthropomorphised, their original niche is filled in by a different species.
To qualify for this trope, it is not a requirement for every species in the setting to have a real-world counterpart. For example, the setting can have giant monsters or magical beasts which, naturally, don't have any real-life equivalent. Regular, mundane animals can also appear in the setting (even if they might have different names). As long as there is at least one species that plays the role of an obviously different real-life species, it counts - but of course, the more such species there are, the better. If the only fantastic species like this is the counterpart to a dog or a horse, add the example to the respective subtropes instead.
This phenomenon, to an extent, exists in Real Life and is called convergent evolution. On different parts of the world and/or in different time periods, species largely unrelated to each other but filling the same ecological role (niche) will evolve similar anatomical and behavioral traits. However, these similarities will usually be superficial. But fiction likes to exaggerate this, with the fantastic species acting virtually identical to their real-world counterpart.
Common in fantasy and science fiction as well as in Speculative Biology. Specific variants include All Animals Are Dogs, All Flyers Are Birds and Horse of a Different Color. If the animals are even named after their real-world counterparts, that's Call a Smeerp a "Rabbit". Compare Animalistic Abomination, where an Eldritch Abomination shows resemblance to a mundane animal; Call a Rabbit a "Smeerp", where the fantastic species is identical to the mundane species apart from its name and small cosmetic differences; and Informed Species, when an animal is intended to be a mundane species but doesn't look much like it. Also compare Fantasy Counterpart Culture and Fantasy Counterpart Religion, where fictional cultures and religions replace real-life ones in a similar manner.
- Rango takes place in a Mouse World inhabited by Funny Animals, but some species, rather than being anthropomorphic, take the place of domestic animals. Roadrunners are the counterparts to horses, and javelinas (small wild pigs) are draft beasts filling the role of oxen.
- Onward: In this Urban Fantasy story, dragons are the equivalents of dogs, whereas unicorns, out of all things, are garbage-eating, hissing pests in the vein of raccoons.
- A Bug's Life: The Ant Queen keeps an aphid as a lapdog, while P.T. Flea uses millipedes as oxen to pull his circus train.
- Cars: In this world of living vehicles, farming machines take place of cattle - tractors act like cows, gently grazing on wheat fields and tipping over when someone honks at them, and Frank the combine harvester acts like an aggressive bull, attacking cars who enter his field. There are also tiny VW Beetles that take the place of insects.
- Dougal Dixon's Speculative Biology books love this.
- After Man: A Zoology of the Future has rabbucks (giant rabbits) in place of ungulates like deer and zebras; giant rat-descendants filling in the role of wolves, weasels and polar bears; penguins in place of whales and dolphins; giant pigs acting like elephants; and many, many more.
- The New Dinosaurs: An Alternative Evolution has giraffe-pterosaurs (even with giraffe colors), penguin-pterosaurs, koala-dinosaurs (yes, they live in Australia), manatee-dinosaurs, pangolin-dinosaurs (called pangaloons), and even naked mole rat-dinosaurs to name a few.
- In the John Carter of Mars books, some of the fauna of Barsoom (Mars) have clear counterparts on Earth. The Banth is clearly a ten-legged lion, the Toath are horses and the Calot are stocky pets similar to bulldogs. The White Apes, despite their name, only look like white, four-armed gorillas, but their ecological role is more similar to large predators like bears.
- In The Stormlight Archive several animals native to Roshar play the role of real-world animals. Chulls are beasts of burden like oxen, axehounds are, well, hounds, songlings are similar to singing birds and cremlings are very much like crabs.
- Expedition: Darwin IV's fauna has a number of species resembling either extant or extinct Earth species. Gyrosprinters are fast, antelope-like herbivores, unths are large tusked arctic beasts similarly to mammoths, prismalopes are the equivalents of rodents, arrowtongues are large predators resembling a Tyrannosaurus rex, prongheads are pack-hunters similarly to wolves while physically resembling velociraptors, etc.
- The Walking with Dinosaurs franchise uses this to some extent when characterizing prehistoric animals.
- In Walking with Dinosaurs, one species of Iguanodon is given zebra stripes, and makes a zebra-like whinny at one point. Utahraptor, a stealthy and fast predator, is given a cheetah-like coloration with black dots on a yellow base, complete with tear stripes. Anurognathus is treated as the Jurassic equivalent of tickbirds, flying on the bodies of sauropods and hunting insects on their skin.
- Walking With Monsters is especially guilty of this. The prehistoric fish Hyneria beaches to hunt amphibians like an orca hunting for seals; Diictodon burrow like reptilian gophers; Lystrosaurus migrate in large herds like wildebeest, crossing rivers where they are hunted by primitive crocodylians.
- The examples in Walking with Beasts are slightly more justified, as wooly mammoths and Deinotherium are actually related to elephants and so are Australopithecus to chimpanzees, so it makes sense that the series treats them as the prehistoric counterparts of these species. Smilodon, however, is portrayed with a social structure identical to modern African lions, which is very unlikely. The most extreme example in the series is Ambulocetus, which is portrayed as a mammalian crocodile.
- Some species in The Future Is Wild fit the bill. Shagrats are the rodent equivalents of musk ox, the snowstalker is a mustelid resembling a polar bear, the gannetwhales (despite their name) are seal- or walrus-like birds. The deathgleaner is a giant bat filling the role of vultures. The flish are flying fish behaving like birds, and the squibbons are squids living in trees like gibbons, with monkey-like social behavior.
- Star Trek: Deep Space Nine has Cardassian voles, which act like generic vermin such as rats.
- Ironclaw takes place in a World of Funny Animals that avoids Carnivore Confusion with several species of "lizard" (read: Domesticated Dinosaurs) and Planimal taking the place of fauna. Allowing, for instance, a boar PC to go on a tusk-melon hunt. There are also constrictor Snake Gourds, bull-like Aurochs Radishes, and many more.
- Warframe, the bat-nosed egg-laying Kubrows serve as a stand-in for dogs while the long-legged Kavats are the equivalent to cats. Both of them can be brought into combat to attack foes and provide numerous bonuses like increased radar range with the right mods.
- In No Evil, jackalopes are used as beasts of burden, treated as the counterpart of oxen or donkeys. Chupacabras, meanwhile, are large, bear- or wolf-like predators.
- Spongebob Squarepants uses this mostly for comedic effect. There are worms in place of dogs, snails in place of cats, seahorses in place of horses and jellyfish in place of bees, out of all things.
- In Amphibia, the Frog Men keep spiders as dog-like pets, ride giant snails similarly to horses or donkeys, and keep giant worms (with cow-like coloration) for dairy. Meanwhile, there are flies that act like birds (actual birds also exist, but they are monstrous predators), and hedgehogs that hunt in packs and cackle like hyenas. Also, an entire episode revolves around a caterpillar acting and looking like a cat.
- The Silly Symphonies short "Merbabies" has a circus parade scene where aquatic animals appear in the roles of typical circus animals. There are carriage-pulling seahorses, octopuses lumbering like elephants (with one tentacle acting as their trunk), crabs swinging in a cage like apes, and a tigerfish with black and yellow stripes roaring like an actual tiger.
- The Flintstones: the eponymous family has a prosauropod dinosaur acting like a dog and a sabre-toothed cat acting like a house cat. Other prehistoric animals replace objects such as vehicles and household appliances.
- Avatar: The Last Airbender and The Legend of Korra's fauna is a combination of real-world animals (penguins, octopi) and Mix-and-Match Critters made from real-life animals. The latter often stands in for their real-world counterparts — turtleducks (ducks with turtle shells) inhabit ponds, polar bear dogs are fearsome predators, et cetera.
- In one humorous scene, Team Avatar was very confused that the Earth King's pet bear was a regular bear and not a Mix-and-Match Critter.
- In the 31st Century world of Futurama, owls have taken over the niche once filled by vermin like mice and raccoons, and can often be seen coming out of holes in walls. Cattle, which are stated to be extinct, have been replaced by giant beetle-like alien creatures called buggalo.
- OK K.O.! Let's Be Heroes: Miniature dinosaurs are the main fauna of the show's world. Pterodactyls soar the skies like sparrows or pigeons, while small sauropods and triceratops skitter around like squirrels. Gar's Bodega even has a baby T. rex as a pet.