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A combination of various other tropes, but basically it goes down like this: A species believed to of be dead (if it existed at all), reappears in modern-day society (or equivalent time period). Reasons for this are numerous, and can include:
- Human interference: Humans, often showing hubris, bring a species back to life with magic or science.
- Lost World: A sheltered world, in which the species has survived despite what is going on in the world
- Preserved / Sealed: Frozen in a glacier, sealed in a bubble dimension, etc.
- Not Dead Yet:
Often, but not always, the said species will come and play in our world.
Examples dealing with Dinosaurs
- The dinosaurs in Dilbert has just been in hiding.
- Jurassic Park: Revived Dinosaurs by Technology. They are now left alone...mostly.
- King Kong: Dinosaurs inhabit Kong's Island. It is a "lost" island, after all.
- X-Men: Sheltered world persevered, despite the immediate outside world be much much cooler.
- We're Back! A Dinosaur's Story: Time Travel brought dinosaurs into modern day new york, and they got to enjoy a circus.
- Ice Age:Dawn of the Dinosaurs: Same idea as X-men.
- In Sir Arthur Conan Doyle's The Lost World, Professor Challenger brings a pterodactyl back to civilization. It escapes while it's being shown off.
- In the videogame Fur Fighters there is a whole hidden world (which you might acutally miss) found by digging down with a seriously large drill. Once down there you find a futuristic Dinosaur society where the titular characters are stars in a children's comic book.
Examples that don't deal with Dinosaurs
- Another one for human interference: in the Thursday Next book series, dodos and Neanderthals have been brought back to life thanks to new technologies.
- Star Trek: Whales became this via Time Travel. Not necessarily a revival (as the actual whales were alive the entire trip), but still an example nonetheless.
- Wolves in Wolfs Rain. Thought to have been extinct for 200 years, actually hanging on in disguise. Not for much longer, though - just until the end of the world.
- On the new series of Doctor Who, the Master uses creatures called the Toclafane as his servants, creatures that the Doctor insists are no more than a Gallifreyan fairy tale. Subverted in that they are not actually Toclafane but cyborg-ified humans.
- Reg Chronotis from Dirk Gentlly's Holistic Detective Agency went back in time in order to save the Coelacanth from extinction, at the price of having the dodo die out.
- The Coelacanth was believed to have gone extinct in the Cretaceous period. Until they were found alive and well in 1938. They're still doing fine.
- A troper was slightly into Cryptozoology a few years ago, and I remember that there are quite a few examples of this in real life, including species that were thought extinct for quite some time, were discovered to be still around, but had been hunted or driven to extinction recently due to development and such.
- the central twist is that the Valkyria, a race believed to be extinct, still live on in the blood of two female characters in the game, and proves the possibility there could be more out there.
- In Syberia, it turns out that woolly mammoths are Not Dead Yet and living on the titular island of Syberia, up in the north.