You read a book about a hero and his faithful pet, but when the book is adapted to film, the hero's pet has been changed into a different species. This is what's known as an Adaptation Species Change.
In the case of domestic animals, especially dogs, there can be an adaptation breed change.
May be part of Pragmatic Adaptation in live action movies and TV shows if the original species was either rare, dangerous, just not easy to work with, there was something else similar handy instead, or the original species was fictional to begin with.
This trope may also apply with the live-action adaptation of a work which has a Talking Animal character, with said animal turned into a human, specially in adaptations for theatre or low budget movies that can't count on CGI or animatronics.
Compare: Adaptation Name Change, Adaptation Dye-Job, Anthropomorphic Animal Adaptation, and Race Lift, where the character remains the same species (human), but a different type of human. Can be the result of Demythtification and Doing In the Wizard if the adaptation is trying to be more "realistic" than the work it was based off.
- In the OVA of Kujibiki Unbalance, Alex is a human character. In the TV series, he's a dog (and also the current student council secretary).
- Lola and Layla in Venus Versus Virus are normal girls with psychic powers in the manga but ageless, artificial humans. in the anime.
- In the original Cutey Honey series, Cutey Honey herself was a Ridiculously Human Robot. In the Shoujo adaptation Cutey Honey Flash, she is a human.
- Lyrical Nanoha:
- Most of the Human Aliens and Artificial Humans were changed into normal humans in Magical Girl Lyrical Nanoha INNOCENT. Yuuno, Zafira, Arf, and Linith were changed to be ordinary pets (Linith was a Decomposite Character who appeared as both a human and a cat).
- The Florian sisters from Gears of Destiny were changed from Ridiculously Human Robots to (potentially genetically engineered) Human Aliens in Reflection.
- Ginga: Nagareboshi Gin:
- In the manga, Rin is a Japanese pine marten that attacks the Kai brothers when they're puppies, wounding them before Ben rescues them. But in the anime adaptation, Rin is a feral dog instead.
- Downplayed by breed in the sequel manga Ginga Densetsu Weed, where there are two English Foxhounds that trail Weed and his pack only to get killed off by Jerome. In the anime, they got changed to Doberman Pinscher brothers named Thunder and Lector. But there is a hint of the Foxhounds still being used over from the manga, one reporting to Hougen that Jet and Missile the Borzois (Rocket's brothers) had failed in their mission to assassinate Weed.
- One of the first The Legend of Zelda manga was loosely based on the first game. The lore of the series was not as elaborate as it later became, and thus the Hylians are referred to as elves. In manga, Link is a half-elf half-human child instead of (presumably) being full Hylian.
- The Godzilla of Godzilla: Planet of the Monsters is a Planimal, not a dinosaur like most other versions.
- In the original Naruto (1997) pilot, Naruto is the son of the Nine-Tailed Fox and is a kitsune in human form. In Naruto the Nine-Tailed Fox is simply sealed inside of Naruto. Naruto is a normal human boy.
- A one-off season of Pleasant Goat and Big Big Wolf called Mr.Wolffy, Mr.Right! changes Wolffy the wolf into a human.
- Balto: The movie is Very Loosely Based on a True Story about the titular Heroic Dog. In real life, Balto was a purebred Siberian Husky, while in the movie, he's half wolf, which his Character Arc hinges on.
- Bambi: The novel's Bambi was a roe deer in (presumably) Austria, but Disney made Bambi a white-tailed deer in Maine because the latter species was more familiar to American audiences.
- Batman: Assault on Arkham: King Shark is made into an augmented cyborg with tough skin and metallic jaws instead of a half-human/half-shark demigod.
- In Flatland: The Movie, the women of Flatland are the same shapes as the men, rather than simply lines.
- In The Snow Queen, the titular queen is heavily implied to be of The Fair Folk. In Frozen, Elsa is a human who was born with the ability to create and manipulate ice and snow.
- In the original Basil of Baker Street books, Professor Ratigan was implied to have been a mouse or a "big mouse." In the Disney movie The Great Mouse Detective, his species is changed to a rat to be more in line with his last name. Doesn't keep him from being in denial of his species though.
- In the original Sherlock Holmes books, and in most other adaptations, Toby is a bloodhound, but in the Disney movie, he is a Bassett hound.
- In the original How to Train Your Dragon books, Toothless was a tiny Common Dragon. In the film, he is now a Night Fury, a rare and powerful dragon type. The books later retconned him into being a young Seadragonus Giganticus Maximus, a powerful, rare type of dragon like the Night Fury.
- Justice League: Gods and Monsters and its tie-in media made Giganta into a Humongous Mecha and Brainiac into a genetically engineered little boy.
- In the original Peter Pan, Nana is a Newfoundland, but in the Disney adaptation, she is a Saint Bernard.
- Edgar Rice Burroughs' original Tarzan stories:
- Sabor was a lioness, but in Disney's Tarzan, she was changed to a leopardess. note
- The apes Tarzan lived with weren't gorillas, but a fictional species of ape (or hominid?) called mangani. The mangani were mortal enemies of the bolgani (the mangani's blanket term for gorillas).
- In the original books, Tarzan has a monkey sidekick named Nkima, but in the classic films and live action TV show he has a chimp sidekick named Cheeta. The gorilla Terk from the Disney adaptation is loosely based on them.
- My Little Pony: The Movie (2017): In the somewhat obscure G1 comic where he first appeared, the Storm King was a burly, troll-like humanoid. In the movie, since there aren't supposed to be any humans or human-like creatures in the G4 world, he was portrayed as a yeti-like creature with satyr-like hooves.
- In Sgt. Stubby: An American Hero, the titular dog, Sergeant Stubby, appears to be a Boxer as opposed to a mixed "bully" breed in real-life.
- In The Call of the Wild, Buck was a Saint Bernard/Scotch Collie mix, but an animated adaptation distributed by GoodTimes made him a German Shepherd.
- Gnomeo and Juliet: In addition to everyone becoming a sentient gnome, the Nurse is a frog, Friar Laurence is a plastic flamingo, and Balthasar is a small mushroom that doesn't speak. What...?
- Legend of the Guardians: The Owls of Ga'Hoole:
- Otulissa and Strix Struma were spotted owls in the Guardians of Ga'Hoole books, but they've become short-eared owls in the movie. This is most likely because of wanting to make the owls have expressive eyes and faces.
- The High Tyto before Kludd (Metal Beak in this movie, while Metal Beak is saved for Kludd). He was a barn owl in the books, but is a sooty owl in the movie. The irony is that the owl whose species is low in the Pure Ones ranks is the leader of said Pure Ones.
- The Felidae film changes the breeds of several of the cats. For example, Felicity in the book is a Russian Blue, but she doesn't fit the Breed Standard in the film (being long-haired instead of short-furred).
- In "The Merchant's Tale" from The Canterbury Tales, Pluto and Proserpina, gods of Classical Mythology, are now The Fair Folk.
- Something similar happens in the 14th century poem Sir Orfeo, a Setting Update of the myth of Orpheus and Euridyce, which replaced Hades with an unnamed "king of the Otherworld".
- The Wicked Years changes a few characters species from the Land of Oz series. For example, Glinda the Good Witch is a fairy however in Wicked she is a normal mortal human who studied magic.
- In The Hidden History of Oz series by Tarl Telford, Glinda isn't an immortal fairy like in Baum canon. She starts out as a human teenager and the daughter of a sorceress.
- In The Muppets' Wizard of Oz, Toto is a king prawn instead of a dog. Justified, since after Dorothy ends up in Oz, Toto is played by Pepe. Pre-tornado, he's seen as an actual prawn in a goldfish bowl. This trope is averted with the Cowardly Lion, though: he's still a lion, even though his "actor," Fozzie, is a bear.
- In Emmet Otters Jugband Christmas, one of Emmet's bandmates is a raccoon called Wendell Coon. In the Jim Henson adaptation, he becomes Wendell Porcupine. This may have been due to the Unfortunate Implications of the word "coon".
- The Finnish version The Men from the Ministry of "Seal of Office" changes the episode's circus seal into a circus bear, since the plot requires it to be confused with something else via pun. In the original General Assistance Department wants seal for the envelope they are about to send into NATO headquarters, where as in the Finnish version they're waiting for a collection letter for their delayed payment on the shipment (collection letter is "karhukirje" in Finnish, literally meaning "bear letter").
- In the stage adaptation of the Disney animated feature Aladdin, Jafar's sidekick Iago is a human instead of a parrot.
- In A dzsungel könyve, a Hungarian stage adaptation of The Jungle Book, Chil is a vulture instead of a kite.
- The 1902 stage adaptation of The Wonderful Wizard of Oz replaced Toto the dog with Imogen the Cow.
- In BIONICLE, the Gukko are a made-up species of orange and silver colored, four-winged, legless cyborg birds with a long, straight beak. In BIONICLE: The Game, the Gukko is a green and yellow cyborg parrot.
- In Martian Successor Nadesico: Prince of Darkness, Hokushin is a human. In Super Robot Wars V, Hokushin is the last Meganoid. According to Banjo Haran, his father gave the Jovian Union the technology to turn into Meganoids.
- Sonic the Hedgehog: In addition to renaming Fang the Sniper to Nack, the localization of Sonic the Hedgehog: Triple Trouble changed his species to a weasel. In Japan, he was a Wolf/Jerboa hybrid. That's why he looks nothing like a weasel, having traits and features that belong to wolves and jerboas instead. Sega of America later tried to Hand Wave this by saying that he's a Weasel/Wolf hybrid.
- In the original Mobile Fighter G Gundam, Master Asia was a regular human. Shin Super Robot Wars changed things up. In this game, Master Asia is an agent of the Dug Interstellar Republic, sent in response to report intelligent life on Earth.
- In the old Hudson Soft game Binary Land, the protagonists are a pair of humans in the original computer versions. In the more well-known Famicom port, they were turned into penguins.
- In the Scootertrix the Abridged series, Rarity was changed from being a normal unicorn, to a changeling that defected from her species.
- In the original Pride and Prejudice, Kitty Bennet is a human being and is the second youngest of the Bennet sisters. The Lizzie Bennet Diaries turned her into Lydia Bennet's pet cat.
- In Dragon Ball Z Abridged, thanks to Ascended Fanon, Mr. Popo is changed from a genie into a Majin, specifically, the future form of Dumplin, the lead of TFS's Dragon Ball Xenoverse Let's Play.
- Rome's eagle, originally a symbol of Zeus, is a golden eagle (Aquila chrysaetos), also called "royal eagle" in some languages. Its use as a symbol was continued by several European states that claimed to be successors of Rome. When the United States gained independence, they deliberately chose an eagle symbol as a throwback to Rome, but made it a bald eagle (Haliaaetus leucocephalus), a species only found in North America.
- The American holiday of Groundhog Day, when groundhogs are alleged to emerge from hibernation and either retreat back underground or stay depending on the weather to come, has its basis in similar European traditions, including an Irish "Hedgehog Day" custom. But there are no hedgehogs native to North America, so an alternative small burrowing mammal was substituted.
- For reasons known only to the North American branch of Epoch, the Walnuts Squirrel family in the Sylvanian Families toys and anime range are marketed as Chipmunks. They were previously marketed as squirrels under the Furbanks family however, but then an renaming exercise took place on the non-Japanese branches and this happened (the International English branches chose to sync the family name with the Japanese family name but gave them first names, in the original Japanese market they do not have first names). Their family name was also changed to Hazelnut, but thats a different trope.