Small Taxonomy Pools

When it comes to Linnaean taxonomy, few of us outside of the related fields know how many species it covers (for the record, taxonomists estimate there have been hundreds of millions of species of life forms on this planet up to now). The number of species we are familiar with makes up less than 1% of even the known species.

Thus fiction will end up showing a few stock species, due to that familiarity. Some groups of plants and animals can have thousands of known species, and fiction will only mention about two. Often this results in Misplaced Wildlife, as the particular species shown wouldn't live in a certain place, but we wouldn't know of the other species that do (unless the writers are Showing Their Work).

There is also a bit of a sliding scale. On the low end, entire phyla (aka divisions) can have just one or two species represented. On the high end, a single family can have about half a dozen species commonly shown. This is regardless of the actual number of species per group.

Filming on location can produce a fair sampling of the local flora, including the species no one much has heard of, but the plants named will still come from a small pool.

Often this trope is because a particular species is featured in a work that puts that species in the popular consciousness, but there are other causes.

Can be Justified. Many kinds of creatures are rarely seen in fiction because they are just as rarely seen in real life. (When was the last time you met a caecilian, mantis shrimp, or a tuatara?)

A Sub-Trope of Small Reference Pools

A Super-Trope to Stock Dinosaurs.

Contrast Improbable Taxonomy Skills, Seldom-Seen Species.

Single Cell Organisms Without Nuclei or Membrane-Bound Organelles (domains Bacteria and Archaea):

 * Bacteria are more often known by the diseases they cause than the actual organisms. Some are often confused with viruses. There are more beneficial, non-pathogenic bacteria than pathogenic bacteria, outside and even inside the human body, but this fact is often overlooked.
 * E. coli is particularly prone to this: the dangerous pathogenic strain O157:H7 is the only strain anyone has heard of, but in reality the vast majority of strains are non-pathogenic and the vast majority of pathogenic strains relatively innocuous. The relatively innocuous kind is living inside you right now.
 * Impressively averted in Moyashimon, which name-checks a number of bacteria and viruses, as well as a number of yeasts and other one-celled organisms.

Organisms With Nuclei or Membrane-Bound Organelles (domain Eukarya) (plants, animals, fungi listed in separate sections):

 * Algae probably don't even have a specific species mentioned, just the group as a whole.
 * Most protozoa featured tend to be either some species of Paramecium or Amoeba. Their vast diversity is usually ignored.
 * Seaweed is actually not a plant.
 * The fact that seaweed is photosynthetic and looks like a plant doesn't help. The same tends to go for other algae, depending on how much there is in one spot. The distinction gets blurred even further when you find out that plants evolved from algae...
 * Seaweed are a polyphyletic group; some are plants, some are chromalveolates (such as kelp), and some fall under a phylum without a kingdom, such as the rhodophytes (red algae).

Kingdom Fungi (often thought to be plants, but a different group):

 * Mold -- Although anyone who's seen food go rotten knows there are several kinds of mold (depending on the color of the rot), no species is known by name. Even Penicillium chrysogenum is just known by the antibiotic based from it, "Penicillin".
 * Yeast -- Also, no species is known by name. It's just commonly known as one of two things:
 * A fermentation agent, although there are still several different kinds of species for that.
 * Whatever species causes yeast infection, which are the species of the genus Candida.
 * Truffle -- Again, just the group known, not any species. And they are only mentioned when someone is making some kind of fancy meal, or getting ingredients for one.
 * Cooking shows will differentiate between black and white truffles. The fact that there is more than one type of black truffle (black Périgord truffle being the good one), or even just more than two types of truffles never gets mentioned. White truffles are rarer than the Périgords and tend to carry a sort of elitist appeal to them... even more than the elitism that plain old Périgords have. Most people can't tell the difference and restaurants have been known to dose the milder white truffles with Périgord oil so the diners taste the distinctive truffle flavor. Scams abound with lesser quality black truffles also being dosed in the same manner and sold for obscene prices.
 * Mushrooms
 * Edible ones might be mentioned by name, such as morels or shiitake. Poisonous ones are invariably called "toadstools" or just "poisonous mushroom" despite the fact that there are an awful lot of mycotoxin-containing species. (If one is mentioned, it will probably be the "Destroying Angel" simply because it has the most Badass name ever. Not coincidentally it's one of the most toxic and most easily misidentified mushrooms in the wild.)
 * In Dresden Files book "Grave Peril" Jim Butcher gets it exactly right with his description of how the eating a Destroying Angel will kill you. He even gets the antidote spot-on.
 * Kind of justified. Some are ridiculously hard to identify without specialized equipment and even mycologists are known to argue about which are which.

Plants (kingdom Plantae):

 * Pteridophyta (ferns) are never referred to by species...ever. There are some 12000 current species and countless others that didn't survive much past the cretaceous period. You can bet that if a work references ferns at all, they will either have mystical properties, or the story in question will take place during the Cretaceous period or earlier (these two options are not mutually exclusive). Bonus (negative) points if anyone makes reference to flowers or seeds of a fern. Bonus (positive) points if someone makes reference to fern spores, or mentions a specific species.
 * The Conifer is an entire phylum of plant species, yet all fiction seems to mention are "Pines" and "Firs" (both of which are genera themselves.) "Redwoods" (a casual name, not a formal taxonomic designation) and "Blue Spruce" (a single species) run a distant third and fourth, and there's very rarely a distinction made between Coastal Redwood and Giant Sequoia.
 * Temperate angiosperm trees are fairly well represented, if only because there aren't that many to choose from, tropical trees, less so.
 * Flowers are mostly those with well known associations - roses for romance, carnations for buttonholes, poppies for remembrance. Characters will very seldom talk about their geraniums and fuchsias.
 * Except for little old ladies who dabble at gardening: geraniums are the flower of choice then.
 * There are three types of grass: lawn, cereal, and bamboo. Adventurers in a swamp may encounter sawgrass.
 * With 22,000-25,000 species in the family Orchidaceae, the one on-screen is invariably one of the most common decorative Phalaenopsis. Extra fail points if it's also Misplaced Vegetation and/or being described as an "exotic new species." Extra bonus fail points if it's called a "species" at all since almost any Phal. you will find in cultivation will be a complex hybrid.
 * Carnivorous plants are never represented as anything but pure fantasy with giant man-eating snapping jaws and writhing vines. There are probably close to 1000 different species of insectivorous plants around the world with New World and Asian pitcher plants, sundew, bladderworts, butterworts and others, many of which are perfectly "weird" and photogenic without any fabrication at all. The Venus Flytrap gets extra props for Charles Darwin calling it "the most wonderful plant in the world."
 * Eucalypts are rarely ever distinguished beyond generic 'gum trees' despite covering a truly staggering number of different species. Even in their native Australia you might get the occasional references to blue gums or the stark white ghost gums but that's about it.
 * In general, unless they are anthropomorphic characters, expect most plants to be treated as objects or scenery. They may get a MacGuffin or Companion Cube treatment if they are non-anthropomorphic.

Animals (kingdom Animalia):

 * The animal kingdom actually includes dozens of phyla, with only one of them covering animals with backbones (or pseudo backbones). We'll try to group them appropriately.

Sponges (phylum Porifera):

 * No one species is commonly shown. It's probably because of SpongeBob SquarePants that many are even aware sponges are living creatures. We hope.

Cnidarians (phylum Cnidaria):

 * You're unlikely to get a view of the diversity of the jellyfish (or jellies, if you prefer). When they show up, it's likely they'll be the common, impressive-looking, and easy-to-handle sea nettles. You're also likely to hear of the infamously-deadly Chironex fleckeri, and it will probably be referred to as the "sea wasp" or "box jellyfish," despite box jellyfish being a whole class of animals.
 * Corals and sea anemones may be seen, but exactly what type they are isn't often specified. However, if brain coral is shown, it will probably referred to as such.
 * You didn't even know hydras are real animals, did you?
 * Imagine you had 5000 conjoined twins, but some have only legs, others only mouths/stomachs, others only gonads, and some forming grotesque air bladders. Welcome to the world of siphonophores.
 * Speaking of Siphonophores, if you asked the common man what a Portuguese Man o' War was, 99 out of 100 times he'll say "jellyfish". While Man o' Wars are jellyfish in the sense that they are in the subphylum Medusozoa, that's where the taxonomic similarities end. Man o' Wars are part of the order Siphonophora in the class Hydrozoa, while the common man's jellyfish is almost always invoking the cup-shaped jellies of the class Schyphozoa.

Echinoderms (phylum Echinodermata):

 * Sea urchins are fairly uncommon. You might see some of the flashy black-or-purple spiky-ball variety sea urchin, but no attention will be paid to them.
 * Despite there being a large number of sea cucumbers available to choose from, they remain incredibly unpopular.
 * Sea stars (or starfish) are one of the most underrepresented animals out there. The only type of sea star that ever appears is the generic five-armed pink-or-tan "Patrick Star" kind. In reality, there are thousands of types of sea stars of various colors, sizes, and arm counts. Some have as many as eleven arms, and can be found in practically any color (though grey and tan are pretty common).
 * The crinoids, or sea lilies, are totally unheard of.

Arthropods (phylum Arthropoda):

 * Includes insects, arachnids, and crustaceans. Except for the crustaceans (usually) most arthropods in media tend to be erroneously called insects or bugs.

Insects (class Insecta):

 * Whenever there are butterflies featured in any series, they are almost always the orange and black monarch butterfly. If they aren't monarchs, they're the white cabbage moth.
 * Beetles, there are beetles for practically every environment and are everywhere. The most recognized beetles out there are Dung Beetles, Rhinoceros Beetles, Stag Beetles, and Ladybugs.
 * Cockroaches are common, but we're never told which of the thousands of species. If they're just used for a gross out or scare in a horror movie, they'll always be Madagascar Hissing Cockroaches, which are vastly different from cockroaches you'd actually find wherever the setting is, but are available at pet stores.
 * Flies in fiction come in one of three varieties: fruit flies, houseflies, and occasionally huge honkin' biting flies, usually referred to as horseflies.
 * Mosquitos aren't considered flies in fiction.
 * Wasps and Hornets are usually called "yellow jackets", build nests like paper wasps, and act like hornets.
 * Bees are honeybees or bumblebees.

Arachnids (class Arachnida):

 * Spiders are usually tarantulas or black widows. The former is most common because they're really large for spiders (which makes them more intimidating to look at), but are also relatively docile for spiders, making them easier to work with (some species do have a painful bite though, and some fling hairs that can cause severe irritation to the skin). Black Widows have a nasty bite and a very distinctive appearance. Any spider that isn't one of the two "dangerous" varieties is "generic harmless" and is probably a harvestman (aka daddy longlegs), the latter of which isn't really a spider. It should be noted that while the harvestman is not a spider, the cellar spider which is also called the daddy longlegs is a true spider. Confusion over the name leads to people claiming the cellar spider is not a true spider (especially in regions where they exist but harvestmen do not.)
 * The emperor scorpion is the only scorpion you'll see in fiction, with very few exceptions. That particular species hits the perfect sweet spot of being huge and impressive looking, mildly poisonous, and very docile.
 * Arachnids are not insects, such a common mistake that a character pointing out "You know that spiders are arachnids, and not insects, right?" is almost its own trope.
 * For that matter, you probably won't find pseudoscorpions, whipscorpions, mites, tickspiders, sunspiders, or anything other than spiders, scorpions and maybe ticks featured in fiction. You probably won't even get an acknowledgement that "arachnid" is anything other than a fancy synonym for "spider".

Crustaceans (subphylum Crustacea):

 * There's lobsters and crabs. Crabs are almost always one of hermit crabs, blue crabs, or Alaskan king crabs. Lobsters only come in one variety in fiction, and to make matters worse, especially in animation, they're bright red. (Live lobsters are brownish-green; they only turn red when they're cooked.) Shrimps are also often colored either pink or orange in advertising, even if they're supposedly alive.
 * Better off than the mantis shrimp, who despite being the living spineless incarnation of Badass, almost never appears in books or other works of fiction. When it does, it is always in aquarium books demanding that one kill it on sight, with the notable exception of Fragment, where several of Henders Isle's nightmarish inhabitants are distant relatives of mantis shrimp (in fact, at one point the characters theorize that this is looking at it backwards: that mantis shrimp originated on Henders Isle.)
 * In The Deep South or during Mardi Gras in New Orleans, you may encounter crawfish. They will be boiled, bright red and an excellent reason to have a beer.
 * Armadillidiids, more commonly known as pill bugs, are fairly common, but you can bet that nobody will actually refer to them as crustaceans.

Myriapods (subphylum Myriapoda):

 * The most common members of this subphylum are centipedes and millipedes. These are often referenced in media, but are often much larger than they should be. They are never painted in a positive light, and are often referred to (mistakenly) as insects, or just dismissed as "bugs." As if centipedes and millipedes didn't get it bad enough, other classes (Pauropoda, Symphyla) within myriapoda will NEVER be mentioned.

Phylum Mollusca

 * Gastropods: one snail, one slug.
 * Cephalopods: A generic octopus, or giant squid.
 * Bivalvia: Alive, they're unseen ; dead, they're lumped together as seashells unless they're oysters, mussels or scallops, in which case they are "food".

Phylum Chordata:
The phylum Chordata contains all vertebrates as well as some more things. It is split into many classes and orders.

Fish (formerly class Pisces, now considered paraphyletic and split into several different classes):
to:
 * Sharks almost always either great whites or hammerheads.
 * Rays very, very rarely appear. Don't expect more diversity than a manta, stingray, or electric ray, and even that's pushing it.
 * Eels come in two flavors: electric (which are actually more related to goldfish and catfish, and are not true eels), and 'other'. Expect 'other' eels to be called "moray eels" even if they are something else (often a rock eel or wolf eel, for ease of handling).
 * A rundown of the current extant fish classes (the rest are extinct):
 * Chondrichthyes, the cartilaginous fishes; best known examples being rays (superorder Batoidea) and sharks (superorder Selachimorpha)
 * Actinopterygii, the ray-finned fishes; what most people think of when they hear the word "fish"; think of salmons (family Salmonidae) or goldfish (Carassius auratus)
 * Sarcopterygii, the lobe-finned fishes; the best known example being the West Indian Ocean coelacanth (Latimeria chalumnae).

Amphibians (class Amphibia):

 * Frogs and toads are usually shown as green or brown and bullfrog-like, and sound like chorus frogs (the generic "ribbit"). For a more exotic setting, red-eyed tree frogs are popular.
 * Salamanders and newts are less common than frogs, but when they do appear, they're given any color and pattern.
 * Good luck finding a caecilian.

Reptiles (class Reptilia):

 * Dinosaurs have likely the widest variety in fiction. Before Jurassic Park, however works were unlikely to show anything beyond sauropods, Stegosaurus, Tyrannosaurus Rex, and ceratopsians.
 * And then that movie added  Velociraptor  oversized generic dromaeosaurid with the name Velociraptor slapped on it to the stock roster. They never get properly depicted with feathers.
 * The third movie made Spinosaurus a household name as "dinosaur more Badass than Tyrannosaurus Rex". Please quietly ignore the fact it was a fish eater and had wimpy jaws, as well as the palaeontologist quietly sobbing in the corner...
 * If you get more specific, the taxonomy pools become smaller:
 * Large theropods are usually T. Rex, Allosaurus, Dilophosaurus, or Spinosaurus.
 * Birdlike theropods are mostly represented by raptors (Deinonychus, Velociraptor, or Utahraptor), Archaeopteryx, and Ornithomimus.
 * Non-birdlike small theropods are pretty much unheard of.
 * Sauropods are represented by Apatosaurus, Diplodocus, and Brachiosaurus.
 * Prosauropod? What's that?
 * The only stegosaur is Stegosaurus.
 * The only ankylosaur is Ankylosaurus.
 * There are two ceratopsids: Triceratops and Styracosaurus, while proceratopsians are unheard of.
 * Pachycephalosaur? Huh?
 * Hadrosaurs are usually represented by Parasaurolophus or Edmontosaurus (whatever name it's referred to as), and neither is likely to be named. Ornithopods other than hadrosaurs are pretty much only represented by Iguanodon.
 * Pterosaurs will always be either Pteranodon, Rhamphorhynchus, or a completely fictional blend of the 2. Always.
 * Plesiosaurs will always be Elasmosaurus.
 * Ichthyosaurs and mosasaurs hardly ever appear.
 * There were several other extinct groups of reptiles, but most of them were probably never depicted in fiction. Good luck finding a rhynchosaur, choristoderan, drepanosaur, thalattosuchian, thecodont, or a procolophonid, among many others.
 * The most common lizards you'll see on TV/Movies are iguanas, chameleons, geckos, the occasional frilled-lizard (if it's set in Australia), and the Komodo dragon. Gila Monsters show up occasionally. Note that if an iguana does show up, it will almost always be a pallete-swapped chameleon or gila monster, sporting a prehensile tongue, color changing abilities and a taste for bugs and small animals. Herbivorous real world iguanas display none of these traits.
 * Snakes in fiction come in five main styles: cobras, rattlesnakes, constrictors (Boas, pythons, and anacondas being the most popular), and "generic deadly" (almost always in fact a false corn snake, which look appropriately poisonous) are the first four. The fifth type of snake is "generic harmless", usually a green garden snake.
 * Somewhat averted in Australian fiction, if only due to the sheer number of venomous snakes available.
 * If it's a turtle, prepare to see either a cute pond turtle, a sea turtle, or a tortoise. Snappers may show up on occasion.
 * When people think of crocodilians, they're most likely going to picture your standard American Alligator or Nile Crocodile. Rarely will you see a Gharial (also known as a Gavial) or a Caiman in a show/movie unless it's for documentary reasons.
 * When it comes to their prehistoric relatives, pretty much the only prehistoric crocodylomorph you can expect to see is Deinosuchus. It's possible to find a Sarcosuchus or some other large species in a documentary or two, but the small, terrestrial, and possibly warm-blooded crocs such as notosuchians are almost unheard of.
 * Tuataras are pretty much only mentioned in documentaries.
 * Amphisbaenians are rarely mentioned even in documentaries.

Birds (class Aves):

 * Birds are technically the only living dinosaurs. As such, if there is anything close to a representative of this is will be the Archaeopteryx, and even that's doubtful. Few extinct birds are ever used - not even the rather awesome Elephant Bird.
 * You will never see a hoatzin in fiction. Nor will you see a sun bittern, or other such birds.
 * If an owl appears, expect it to come in either snowy, great horned, or barn owl flavors. More spectacular owls like the burrowing owl or the eagle owl are either ignored or just marketed as up-scaled regular owls.
 * Non-owl birds of prey in fiction tend to be red-tailed hawks, peregrine falcons, bald eagles, or very occasionally, ospreys. You will never see a Secretary Bird, which is a giant eagle on stilts.
 * Interestingly, averted by The Mummy Trilogy, in which Ardeth Bey's falcon Horus is not a peregrine, but rather a very area-appropriate saker falcon.
 * Penguins will either be emperor penguins or adelie penguins (better known as big ones that live in Antarctica or little ones that also live in Antarctica). They will always be shown desiring a frigid cold environment, despite living up to tropical areas and their defining environment being beaches. They might also be noted for their love of fish.
 * Parrots will always be brightly-coloured, mostly red or commonly green, and will be able to talk fluently. Cockatoos, large white parrots with moveable head crests, are rare; black cockatoos, including the highly intimidating but gentle Palm Cockatoo, aren't seen. There will be no concept of a parrot shorter than your arm unless it's a budgie, which will always be yellow and green and called a 'parakeet'. And there will never be a mention of the heavy and rare Kakapo, nor of the fearless and destructive Kea and Kaka - all three being New Zealand birds and dark greenish brown.
 * Well, the Kakapo is becoming a bit more popular in internet works, but its almost always because it's shagging you.
 * Specifically, the most commonly shown big parrots are Amazons and Macaws, and even then, it's usually Yellow-Headed Amazons, Blue & Gold Macaws, or Scarlet Macaws. The small Hahns and Noble Macaws don't appear at all. When Cockatoos do show up, they're usually the huge white Umbrella or distinctive Sulfur Crested - forget the smaller Goffins, Bare-eyed, Rose, and Major Mitchells varieties. African Grays hold some popularity since Alex and are primarily Congos. Any sufficiently tropical location may have Lorikeets, either Green-Napped or Rainbow. 'Parakeet' actually refers to any bird with long tail feathers, which includes Macaws and a huge variety of other parrot species that even don't blip the radar. Such as Sun Conures and Cockatiels, despite their huge popularity in the pet trade. That's not even mentioning the many hundreds of types of short-tailed parrots. Anyone ever seen a Caique, Hawk Headed Parrot, or a Pionus?
 * A few other birds used fairly often include the ostrich, generic robin, sparrow, or swallow, vulture (anywhere they're needed to show that something is dead), peacocks, and occasionally the kiwi. Chickens and turkeys are either trying to avoid becoming a meal or already one.
 * Ducks will usually be mallards (wild or domestic) and geese will usually either be Canada geese or grey geese (usually domestic).

Monotremes (subclass Prototheria)

 * The platypus is the only monotreme showing up in fiction. The hedgehog-like echidnas are rarely (if ever) heard of, even in documentaries.
 * An exception is made for fiction in which Australia is the main location.
 * Or in the Sonic fandom.

Marsupials (infraclass Metatheria)

 * Marsupials arguably have more diversity in their hundreds of species than any other variety of mammal, yet the amount of species used in fiction could be counted on a few fingers. Kangaroos and koalas are obviously the most popular, and instantly come to mind at the word "marsupial". Opossums (which will probably be referred to as possums, actually a name for a different animal altogether) are familiar due to being so common in the United States.
 * You will never see a quoll in fiction, even a story set in Australia.
 * There is only one Bandicoot.
 * Here is another one. Kinda. (Warning: Yelling Bird speech-bubble is not exactly appropriate for work environment).
 * The only American marsupial ever portrayed in fiction is the Virginia Opossum - there are apparently close to 100 opossum species ranging from the semi-aquatic yapok to primate-like woolly opossums to mouse opossums with no pouches. Aside from the true opossums there are two other orders of marsupials in the Americas: the so-called Shrew opossums and the Monito del Monte, the latter bizarrely grouped with the Australian marsupials despite its locale...

Placentals (infraclass Eutheria; regular mammals)

 * Primates have a wide variety, even counting humans (since we show up by default). We have gorillas, orangutans, chimpanzees, baboons, and a few monkey species. No bonobos, though.
 * If someone has a pet monkey, it will almost always be a capuchin. This particularly stands out in fiction set in Africa or the Middle East, since capuchins (like all monkeys with prehensile tails) are New World monkeys - that is, only native to the Americas.
 * Cats. Since the domestic cat is a species (Felis catus), all breeds count. Then we have tigers, lions, pumas, panthers, leopards (or jaguars, which will often be mistaken for the other and vice versa), and cheetahs. The medium-sized cats like the ocelot, lynx and serval are virtually never used. You will never, EVER see a kod-kod or fishing cat. If it's set in prehistory, the only felines are saber-toothed cats, specifically Smilodon fatalis, which is only one of many saber-toothed cats.
 * Dogs have a few shown. There are the domestic dog breeds (all one subspecies of wolf: Canis lupus familiaris), the wolf, the fox, and the coyote. Dingos may be used if the work is set in Australia. Once in a while jackals or hyenas will show up. (No, hyenas aren't canids - they're more closely related to the cats.)
 * And even among domestic dogs, only a few breeds show up unless the writers are trying to cram as many breeds in as possible. Most of them are Labs, German Shepherds, Dobermans, English Bulldogs, Dachshunds, Poodles (often miniature or toy), Golden Retrievers, Chihuahuas, Great Danes, that sort of thing. When did you ever see a Pharaoh Hound, a Portuguese Water Dog, or a Boston Terrier (though those are slightly more popular in ads) in literature or television?
 * If the work is about dog sledding, the dogs tend to be Siberian Huskies regardless of the original work or the preferences of the mushers of the time.
 * Borophagine and hesperocyonine dogs are quietly swept under the table.
 * When we think of bears, we think of the grizzly, the black bear, the polar bear, and the giant panda (which, by the way, was found to genetically actually be a bear ).
 * Spectacled bears, despite being the only surviving cousins of the Badass short-faced bear, never appear.
 * Lions and tigers and bears, oh my! If they need a large, land-based predator, 90% of the time it will be one of those.
 * Regarding smaller carnivora, among the most familiar seem to be raccoons and skunks. Members of the Mustelidae family aren't seen so often in fiction, but there are a few commonly-used stock species. Smaller varieties will be ferrets when something cute and playful is called for, or weasels if a sinister creature is in order. Next in line are ever-popular otters, followed by less-often-seen badgers, and the occasional wolverine (far less common than the X-Man bearing their name).
 * Mongooses are essentially known in fiction solely for their cobra-killing reputation, and are sometimes even called weasels. Good luck finding any civet or genet in fiction.
 * Civets did appear a lot in the Nancy Drew Files book "Scent Of Danger".
 * Thanks to The Lion King and Animal Planet, meerkats have surpassed other mongoose species in popularity. Now, you seldom see regular mongooses, either.
 * Of the order of cetaceans, we have the bottlenose dolphin for dolphins (thanks to Flipper) and for whales we have the Orca/Killer Whale (even though it's actually a dolphin), Humpback, Sperm (used to be the most common depicted whale likely because its oil made it the most valuable to whalers. so this is an association that dropped due to Values Dissonance), and Blue, pretty much in that order.
 * A character pointing out that killer whales aren't whales is a trope in itself. Nevermind that toothed cetaceans (sperm whales, killer whales, bottlenose dolphins) are all more closely related to each other than baleen cetaceans (humpback whales, blue whales), making the "whale/dolphin/porpoise" distinction rather meaningless.
 * Beaked whales are NEVER shown. Not ever, though considering how elusive and poorly-known they are, that's not surprising.
 * Unless you're watching a documentary, don't expect to see the whales' land-based ancestors.
 * Don't expect to see too many freshwater dolphins either, like the pink dolphins of the Amazon River and its tributaries.
 * Bats usually come in three standard forms in fiction. You've got your standard insect-eating bat, your cute flying fox bat (AKA a fruit bat), and your creepy vampire bat. Don't expect to see a frog-eating bat anytime soon...unless you're watching a nature documentary.
 * Rodents are usually known for mice, rats, squirrels and chipmunks. Less used, but still relatively familiar are beavers and porcupines as wild animals, and hamsters, gerbils and guinea pigs as pets. The low ranking is especially odd as the order of rodents is the largest mammal order, with 40% of mammal species in it.
 * And almost all rodents seem to be confused or mixed together to form some sort of new creature. Mice and rats are commonly confused, especially wild ones and pests (which are ALWAYS diseased and filthy in fictionland. Even some pet ones are depicted this way). Usually you see a character screeching and screaming or going "YUCK" and calling what is usually a mouse a rat. You also have the people who call every rodent a rat. Which unfortunatly is Truth in Television for many.
 * Similarly, guinea pigs are constantly confused with hamsters, even though they hardly look alike (Google either and you will eventually see hamsters in the guinea pig search, and guinea pigs in the hamster search). They are usually depicted with running wheels and salt licks and seeds, when all three of these are extremely unhealthy and even dangerous for guinea pigs. They are also often drawn the size and shape of hamsters, and only called guinea pigs for plot reasons (such as they are being experimented on, or the creators thought "guinea pig" sounded cooler/more mature/wanted to avoid being connected to Hamtaro).
 * Rabbits sometimes get lumped in with rodents, too. Actually, they're lagomorphs, and if you see a lagomorph, it's probably going to either be a cottontail if it's a rabbit or a jackrabbit if it's a hare. And no one ever talks about pikas, unless it is joined to a -chu.
 * Bless you!
 * Ferrets are also lumped with rodents, sometimes.
 * Which is Older Than Feudalism, apparently. The Latin name for such creatures, Mustelidae, roughly translates to "mice as long as spears."
 * The mammals pertaining to the now obsolete order Insectivora tend to be represented by the mole, the shrew and the hedgehog. Moles tend to look always like the european mole (except for the Redwall animated series where they were star-nosed moles, which are not native to England and therefore aren't native to Mossflower either).
 * And the other members of the Insectivora who got booted out? They're never appear either. Sorry tenrecs and elephant shrews.
 * Colugos (order Dermatoptera) or tree shrews (Order Scandentia) are never shown. Never mind that they're our closest non-primate relatives.
 * In fiction, artiodactyls will be livestock (usually cattle) on farms, deer in temperate climates, antelope (usually gazelle or wildebeest) in the tropics, camels in the desert, or caribou in the arctic. Period pieces might add bison (called buffalo, natch) to the American West. For works set in the North Woods of North America you may see moose. No further description or species distinctions are given or expected, because herbivores are harmless and therefore boring.
 * Horses in fiction come in four types: Draft Horse (usually a Clydesdale), Race Horse (almost always a Thoroughbred despite many other breeds being used for racing as well), Wild Horse (mustang), and Generic Critter-You-Sit-On (all others). Mules appear much more often than donkeys, despite needing the latter to create the former. Zebras are treated as one species, often wrongly depicted as the size of modern domestic horses. Rhinos, often also treated as one species, appear mostly in documentaries or (rarely) as musclebound thugs in cartoons. Tapir? What's that?
 * Elephants are nearly always African in cartoons, because big ears are funny. They're nearly always Asian in movies or on TV, because they're the only ones you can actually have on set. Outside the Discovery Channel, all extinct proboscideans are mammoths and all mammoths are wooly.
 * And good luck finding the rest of Afrotheria in pop culture. Maybe an aardvark or sirenian if you're lucky. Hyraxes, golden moles, tenrecs, and elephant shrews are nowhere to be seen. Never mind all the extinct afrothere groups...
 * Of the two extant species of giraffids, the giraffe is all but guaranteed to appear when an African savanna is involved. Meanwhile, you can probably count on one hand the number of fictional works in which you've seen an okapi. Prehistoric documentaries never contain their many extinct relatives, which are actually much more similar to the okapi than the giraffe.
 * Xenarthrans may occasionally be shown in the form of generic armadillos or sloths, or giant anteaters. Ground sloths and glyptodonts are popular if the subject matter involves prehistoric mammals. The tree-dwelling tamanduas (lesser anteaters) and silky anteaters are never shown.
 * Chances are the only time you'll see a mink or a stoat in fiction is as a coat.

Other (extinct)

 * You will never ever see someone refer to a non-mammalian Therapsid or any other non-mammalian member of the Synapsida class. Regardless as to how cool they might be.
 * Well, Dimetrodon is a non-mammalian member of Synapsida and yet it does occasionally appear in fiction... though it's frequently shown coexisting with dinosaurs and even labeled as dinosaur itself.