Monsters include malformed or misshapen animals or humans and creatures of great size. A great number of incompletely documented reports exist of various kinds of monsters. It has not been determined whether such reports correspond in fact to real, undescribed animals (possibly isolated descendants from prehistoric species), to mutations, or whether they are entirely due to different forms of hallucination or optical effects, possibly triggered by natural phenomena.
Such creatures as the dragon, the griffin, the hippogriff, the winged bull of the Babylonians, the winged elephant of the Hindus, centaurs, satyrs, the Minotaur, Lamia, the Bun-yip of Aboriginal Australia and Burr-Woman and Pot-Tilter of the North American Indians are a part, and perhaps a necessary part, of human consciousness since prehistorical times. A great number of monsters have been reported in the 20th century including: the Loch Ness Monster; Yeti or Abominable Snowman; Bigfoot and creatures from Unidentified Flying Objects.