Cryptids are animals which are generally believed to be legendary in mainstream biology. These animals are studied by people known as cryptozoologists, who are either interested in proving that they exist, or interested in studying the myths and cultural beliefs which have arisen around such animals. Strictly speaking, cryptids are not mythological; creatures like unicorns, for example, are not considered cryptids, because they are accepted as myths. Rather, cryptids are animals which some people think could actually exist.
In some cases, cryptids are rediscovered extinct species, or animals which people originally thought were hoaxes. In these cases, the animal is considered a cryptid because only a few unverified sightings have occurred, but eventually enough scientific evidence accumulates to prove that the animal really does exist, in which case it is no longer a true cryptid. One example of this is the coelacanth, a fish thought to be extinct until living versions were discovered. Another is the platypus, which European scientists thought was a hoax until numerous proofs were brought back to show that it really did exist.
Other cryptids include humanoid creatures such as the Abominable Snowman or Yeti and Sasquatch, also known as Bigfoot. Creatures like the Loch Ness Monster, known affectionately as Nessie, are also considered cryptids. Other legendary animals may be more animal like in nature, such as the chupacabra, drop bear, Northwest Tree Octopus, and the Montauk Monster.
Some supporting evidence does exist for most cryptids. This evidence can include reported sightings, historical claims, grainy images, and sometimes even video. However, the evidence does not hold up to rigorous scientific examination, and thus is not accepted by the scientific community. On occasion, scientific rejection of these animals has resulted in egg on the face of scientists as zoologists manage to verify that a supposed cryptid really does exist; several animals believed to be extinct, for example, have been rediscovered and treated as cryptids for some time before the evidence finally indisputably proved that they exist.
Many cultures have legends featuring mysterious animals, with various versions of legendary beasts swimming, flying, and crawling across all the corners of the Earth. In some cultures these legends are treated primarily as fun fiction, and not taken seriously, while in others, people genuinely believe that these cryptids exist. They may ascribe various social and cultural problems such as the loss of livestock or disappearance of children to these legendary animals, for example.