Example; A researcher working away in the bowels of a museum comes across an uncatalogued skin that she does not recognize. Documentation states that it was collected in the Amazon basin in 1893. A cross check of all available literature fails to turn up any further reference. However, the skin is real, and the animal definitely existed at some time. (Actually stuff like this happens often, and it will probably continue for quite a while.) If our hypothetical researcher decides to mount an expedition to find live examples, they are now stepping into the realm of Cryptozoology, as the search is now on for an unknown animal. Much of Cryptozoology is concerned with exactly this, a search for animals that have not been seen for a long time, and are considered extinct by most authorities. Recent examples would be the Thylacine or marsupial wolf of Tasmania, the Moas of New Zealand, and the Passenger Pigeon of North America. The approach that many researchers take is definitely unscientific, overly credulous, and naïve, but it is possible to take a scholarly, respectable attitude. After all, many animals declared extinct have been found alive and well, and sometimes in healthy populations. The Chacoan Peccary, previously known only from Ice Age bones, was found alive in South America, the Bermuda Petrel was declared extinct twice yet still cruises the Atlantic Ocean, and just within the past few days it has been announced that the Cuban Solenodon, a primitive shrew-like mammal, has been rediscovered.
There is one major snag with these findings as it relates to our subject; few if any such discoveries have been anticipated in the Cryptozoological literature. They are continually looking for long lost animals without success, but missing the real ones tripped over by undergrads tromping the bushes gathering mundane data on bird droppings. A glaring case would be that of the Coelacanth, that well known ancient fish rediscovered off the Comoros Islands in 1938 after about a 65 million year hiatus. For years some Cryptozoologists have whispered about a supposed population in the Caribbean, but a few years ago a doctor on honeymoon in Indonesia discovered one for sale at a local fish market. Subsequent searches have confirmed a new population there, perhaps a distinct species. If you wanted to find a sea further from the Caribbean, you would have to walk in the footsteps of Armstrong and Aldrin.