In Period Pieces, animals that didn't exist during that period will often exist either way. Animals that looked different in the past will also appear in modern form for similar reasons.
This is often done due to ignorance. Animals are mistaken for older than they actually are and thus are shown before they existed. This can also be done for recognizability; people will recognize a Bloodhound but not its now extinct ancestor, the Talbot Hound.
In live-action, this trope might be used for pragmatic reasons. It's more expensive and difficult to find period-accurate animals, assuming they aren't outright extinct.
Compare to Artistic License Biology, Artistic License History, Artistic License Paleontology, Misplaced Wildlife, Present-Day Past, Schizo Tech, 1 Million B.C. (for when prehistoric animals and humans are lumped together in a vaguely prehistoric setting), and Science Marches On (for when at the time it was believed the species did exist during the setting's time period, but later analysis and studies show it to be a different but related animal instead).
- Tyrant: The story is intended to be a close-to-real restoration of the world of the Tyrannosaurus, but, with the exception of Quetzalcoatlus, all of the species depicted (Maiasaura, Styracosaurus, Chirostenotes, Pteranodon, and Dromiceiomimus) coexisting alongside it are from the earlier Campanian epoch (while T. rex is known only from the late Maastrichtian, several million years later). This was pointed out to the author by palaeontologists after the second issue, who responded by cutting out most of the offending anachronisms in future issues (with the exception of Chirostenotes).
- The Aristocats came out in 1970 but takes place in 1910. It features a Basset Hound character that has shorter limbs and longer ears than Basset Hounds of that period.
- Lady and the Tramp features two "modern"-style Siamese in the 1900s. The modern Siamese style, with its elongated muzzle and triangle-shaped head, didn't begin development until the 1950s. Prior to that, all Siamese were rounder and less exaggerated looking.
- Pocahontas: Percy, the decent pampered pet Pug of the bigoted, gold-obsessed villain Governor Ratcliffe, looks like the very exaggeratedly brachy modern day Pug of the 1990s when this film was made. Pugs originated in China and were introduced into Europe (into the Netherlands and into England later) in the 1500s. The movie is set in 17th-century Virginia in the New World. Pugs back in the 1600s had much longer muzzles and limbs than modern-day Pugs, so Percy is anachronistic for his time.
- The Dingo Pictures film Dinosaur Adventure features tons of these, since Dingo recycles their animation assets all the time. It's supposed to be the age of the dinosaurs, and yet there are gorillas, crows, monkeys and gazelles running around. On the other hand, this is surprisingly averted with the duck narrator, since waterfowl first evolved in the late Cretaceous period (she is a very modern-looking waterfowl though, making it more of a Downplayed Trope than an aversion).
- The Great Mouse Detective:
- Toby the Basset hound more closely resembles a Basset hound from the 1980s, since he has more exaggerated and easily tripped on ears, far more excessive eyebrow, eye, and torso skin, somewhat shorter legs and far more exaggerated flaws than a real Basset hound would have in 1897.
- Averted with Felicia the Persian. She is a traditional or doll-faced Persian that would likely show up in the movie's time period. Modern Peke-faced Persians developed during the 1960s and only became popular in the 1990s (after the film came out).
- Disney's Dinosaur takes place in the age of dinosaurs, but the protagonist Aladar's mammalian surrogate family look like modern sifaka lemurs. Although the earliest primates did evolve before the K-T extinction, they almost certainly didn't look like their modern descendants. The film also features dinosaurs from both the early and late Cretaceous periods existing in a single time and place, and one of the supporting characters is a Brachiosaurus (a Jurassic dinosaur).
- The Ice Age franchise features a number of relatively obscure prehistoric mammals and birds that were long extinct by the ice ages. This includes brontotheres, Moeritherium, Platybelodon, Chalicotherium, Gastornis, and Hesperornis. The movies also feature Mesozoic reptiles, but their presence is acknowledged as anachronistic: there are sea reptiles that were frozen for millions of years, and dinosaurs that live in an underground Lost World. The Series Mascot Scrat was a fictional species at the time the movies were released, but an uncannily similar species, Cronopio, was discovered since then — which lived in the Cretaceous period, over 90 million years before the ice ages; interestingly enough, another saber-toothed squirrel appears and becomes Scrat's love interest in the third film — the same one with the other dinosaurs — and is "appropriately" placed in the subterranean Lost World with the dinosaurs.
- Fantasia's Rite of Spring sequence features a Dimetrodon, a creature that lived before dinosaurs evolved. The famous fight between the Stegosaurus and a Tyrannosaurus rex is another example, given that the T. rex and Triceratops (which is also present in the sequence) existed in the Cretaceous, millions of years after the Stegosaurus. Other dinosaurs of the Jurassic and Cretaceous periods (along with a few Triassic critters such as Kannemeyeria) are shown as living side-by-side throughout.
- The Land Before Time has a plethora of animals from various time periods in the Mesozoic era living together, as well as a few animals that lived before or after the Mesozoic such as the Dimetrodon (Permian) from the first film and the horned gophers (Miocene-Pliocene) from one episode of the TV series.
- 10,000 BC:
- The characters ride upon modern-day horses. The problem is, horses in prehistoric times looked nothing like their modern day, more domesticated, descendants. The horses should be much stockier, have upright manes, and be plainer looking (overall being closer to a donkey than a modern horse).
- On the opposite end of the spectrum, giant terror birds like Titanis went extinct around two million years ago and were definitely not around 10,000 B.C.
- Jurassic World: Dominion: The opening prologue is explicitly set at the very end of the Late Cretaceous, but of the numerous animals depicted (Dreadnoughtus, Giganotosaurus, Oviraptor, Nasutoceratops, Pteranodon, Queztalcoatlus, Moros, Tyrannosaurus, and Ankylosaurus) only Tyrannosaurus, Quetzalcoatlus, and Ankylosaurus are from the correct time, with most of the others living many millions of years earlier (never mind that most were also separated spatially as well).
- This is nothing, however, compared to One Million Years B.C., which cheerfully threw together humans, dinosaurs (of both the Cretaceous and Jurassic periods, naturally), and even a Giant Spider.
- Narrowly averted in The Name of the Rose movie adaptation. There's a scene including a short shot featuring pigs; the director intended to use modern, pink pigs but the historical consultant pointed that pink pigs were anachronistic and medieval pigs were black or brown. Since they couldn't find black pigs in time, the pigs were dyed for the shooting.
- In The Jungle Book, the live-action remake of Disney's animated Jungle Book, King Louis is depicted as a Gigantopithecus, an extinct species of ape that predates modern humans (such as Mowgli and whoever could have constructed the ruins) by at least a hundred thousand years. This was ostensibly done to prevent the Misplaced Wildlife of The Jungle Book, but an orangutan somehow finding its way from Indonesia to India is a lot more plausible than a Gigantopithecus surviving into the Common Era.
- Bridgerton: The Sharmas have a beloved Pembroke corgi named Newton. Corgis were not lapdogs in the show's setting of 1810s England, let alone India (they were bred as working dogs in Wales and were not recognized as a breed until around a century later).
- Temtem: In-universe, Mawmense's Tempedia mentions that it was featured prominently in a historical movie even though Digital Temtem were only invented recently.
- Arthur, King of Time and Space makes Sir Gilbert the Bastard's dog a rough collie for the sake of a Timmy in a Well gag. Modern collie subbreeds only became a thing in the 19th century. (In The Rant, Gadzikowski notes that he didn't know if collies existed in the 5th century, but says it's wrong either way since Gilbert's dog is supposed to be a hunting hound.)
- The Flintstones features Dino, their pet dinosaur, and the dinosaurs at the quarry where Fred works.