In the middle ages, allegory was commonly used for interpretive information. Creatures of these allegories would be detailed in large bestiaries starting in the 12th century. These bestiaries often included descriptions on "exotic" creatures and where they could be found. Often, they would be said to come from very distant lands where people would be unable to visit them. Each of the creatures' descriptions also left room for a moral less. For example, the phoenix represented christianity and urchin represented the Lord's gift toward the humble. This allowed for people to contemplate the differences between reality versus fiction and animals versus humanity. People began to associate the qualities of these beasts with qualities of humanity. The viper represent patience for the spouse and the crane stood for social collectivism, to name a few.
Crane in its vigilance. Unknown Author. Public Domain.
Ideas of fantastic beasts were further propagated by figures like Alexander the Great in mosaics depicting his journeys. People often had no reason to discount these creatures or had no way to disprove their existence so they accepted that the world was populated by mythical or exotic animals. Similar to a bestiary, in the 6th and 7th century Liber Monstrorum made a collaboration of tales people had of wildly exaggerated creatures. He warned his readers to make their own assumptions about the veracity of his book. However, people often took these as factual.
Beaverbullocks. Anonymous Scribe. Public Domain.
By the mid 1800s, almost all land masses had been discovered and explored. This, of course, meant that most land animals had been discovered. For the first time in thousands of years, people had to admit that their fantastic beasts may not exist. At this point, critics became more prevalent and would try to discount all the other beasts who remained a possibility. They explained that these creatures often resemble something that is known to be true - Bigfoot resembles a bear, for example. In the eyes of Peter Dendle, a Penn State English professor, "We perpetuate Bigfoot beliefs from an apparent psychological need to crystallize fascination with primitivism and animalism into a concrete symbol." In other words, historically these creatures served as possibilities and wildly unique ideas. By the late 1900s, though, they served a much different purpose as people began to worry humans may be the cause of the 6th great extinction. These creatures, though heavily disputed after the discovery of most land, served to repopulate the world to alleviate some guilt felt from humans' destruction.
For some localized history, watch this video on Hoosier Cryptids from Animal Planet.
Dendle, P. (2006, August). Taylor & Francis. Retrieved April 2020, from https://www-jstor-org.ezproxy.butler.edu/stable/pdf/30035486.pdf?ab_segments=0/basic_SYC-5152/control&refreqid=search:df74a7cdb084dc97f16b956e637211d5
Shea, R. H. (2016, August 4). The Science Behind Bigfoot and Other Monsters. Retrieved from https://www.nationalgeographic.com/news/2013/9/130907-cryptid-crytozoology-bigfoot-loch-yeti-monster-abominable-science/
Shea, R. H. (2016, August 4). The Science Behind Bigfoot and Other Monsters. Retrieved from https://www.nationalgeographic.com/news/2013/9/130907-cryptid-crytozoology-bigfoot-loch-yeti-monster-abominable-science/