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, Anachronism Stew, 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).
- The Aristocats came out in 1970 but takes place in 1910. It features a Basset Hound character that doesn't resemble Basset Hounds circa 1900-1910. He has shorter limbs and longer ears that 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 orignated 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.
- The Great Mouse Detective:
- Toby the the Basset hound although more moderate than show Basset hounds in the 1980s and especially since, he has more exaggerated and easily tripped on ears, far more excessive eyebrow, eye, and torso skin, somewhat shorter legs, far more exaggerated flews, than a real Basset hound in 1897, London, England or elsewhere, would have.
- 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 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 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.
- 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 one million years ago and were definitely not around 10,000 B.C.
- 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 anachronic and medieval pigs were black or brown. Since they couldn't find black pigs in time, the pigs were dyed for the shooting.
- 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.)