There is a sub-genre of literature that specifically focuses on fiction that involves Cryptozoology and the beasts that Cryptozoologists study such as new and undiscovered species and species that survives after extinction. This type of literature is called Cryptofiction. You can easily find novels and stories that fit this sub-genre by looking at lists such as this and this. Many famous novels including Hound of the Baskervilles and even Jurassic Park fall under this sub-genre.