An interesting case study would be the Loch Ness Monster; a creature attested as far back as St Columba's early medieval hagiography before its resurgence in the mid 20th century. As we'll see, shifting cultural and scientific paradigms completely altered the ways in which people from the same geographical location "constructed" their monster.

To pre-modern Europeans, a monster’s physical form was significant because its composite parts or overall bodily shape held some kind of metaphorical or allegorical significance. Whether their forms were interpreted by pagans or Christians, animalistic monsters seem to have been more important as vehicles of symbolic meaning than as flesh-and-blood entities to be found in the wild. Many believers in the Loch Ness Monster regularly cite the existence of similar creatures in early medieval Irish hagiographical literature, notably the Life of Saint Colum Cille, who banished a reptilian monster in the River Ness adjacent to the Loch, as historical evidence for the existence of some prehistoric creature. I will briefly situate these occurrences within the symbolic rather than scientific pre-modern worldview to highlight the allegorical significance of monstrous animals. Dáithí Ó hÓgáin’s article “’Moch Amach ar Maidin dé Luain!’” explains that reptilian lake monsters are a surprisingly common trope in early Irish secular literature, hagiographies and oral tradition; in each instance, a monstrous reptilian creature terrorizes the nearby countryside, devouring livestock before being challenged and slain by a hero (whether he be a pagan warrior or Christian saint), turning the lake red with its blood. Ó hÓgáin explains that this trope may be the synthesis of several forms of symbolism where the reptilian lake monster represented paganism enslaving the Irish population before being routed by the powerful Christian saint (which popular tradition concretized from a metaphor to a literal representation of a monster) while the dramatic narrative of martial heroes overcoming lake monsters predates hagiographical sources, suggesting pre-Christian origins.

Serpents appear to have held important symbolic significance in pre-Christian Celtic art. Because of their ability to disappear into impossibly small crevices beneath the ground, regular shedding of their skin and incredible reproductive capacities and movement which mimics the meandering of slow-moving waterways, snakes were likely associated with the underworld, fertility and regeneration by pre-Christian Celtic speakers. Celtic societies regarded bodies of water as liminal spaces between a supernatural otherworld and the physical world (explaining the overwhelming amount of votive offerings found across the Celtic speaking world in bogs, streams, rivers and lakes), meaning that the combination of the otherworldly serpent with the liminal space between worlds would have had a significant symbolic meaning to pre-Christian Celtic speakers. In such a cosmology, the lake serpent would have represented a believable manifestation of otherworldly power on earth, and its defeat by a mortal hero would have accentuated his martial prowess, an important concern in a society dominated by a warrior-aristocracy. In this context, the physical existence of the lake monster would have been less important to the pre-Christian and early Christian audience than the respective symbolic meaning that it represented; the overcoming of a powerful otherworldly entity by a mortal warrior-hero and the overcoming of pagan influence by a virtuous saintly hero.

Similar, later Christian monster narratives used their subject’s bodies as vehicles to convey symbolic meaning. Using ancient Greek compilations of marvels and wondrous creatures, St. Augustine laid the foundations for the medieval genre of Bestiaries by demonstrating God’s power through the existence of seemingly impossible natural creatures, with the added goal of compelling believers into marvelling at God’s creation. Like modern believers in monsters, medieval Europeans did not consider monstrous animals as ‘unnatural’ (or contra naturam) but instead considered them ‘natural’ members of God’s creation who were intended to relay some kind of symbolic meaning to those who viewed them as Isidore of Seville explained: “portents and omens [ostenta], monsters and prodigies are so named because they appear to portend, foretell [ostendere], show [monstrare] and predict future things… for God wishes to signify the future through faults in things that are born…” One was not required to personally witness such a monster to glean symbolic meaning from its form or behaviour as medieval Bestiaries listed fantastical creatures alongside more mundane ones with a moral lesson in each entry; descriptions of mermaids drawing in sailors to their dooms were meant to teach that one should always be wary of flattery.

Modern observers, it seems, are obsessed with the physical composition of their monsters not because their composite parts may reveal some portentous symbolism, but because the post-19th century western episteme forces them to rationalize the existence of their monsters within a scientific context. This change came about in an astonishingly short amount of time – it took only some four decades of scientific research, analysis and theorization to completely change the West’s understanding of the natural world, the creatures that inhabited it, and their own relationship to both. The scientific fields most crucial to this intellectual revolution were the sister disciplines of geology and palaeontology, as a rapid succession of discoveries in both completely challenged the established episteme.

How was this episteme established? I don't think it's necessary to provide a play by play of the intellectual revolutions of the early modern era and 19th century, but to give you a short run down; in the late 18th century a French savant named Georges Cuvier published a paper detailing his studies of fossil mammal species which proved that at some time in the earth's history, distinct and separate species of rhino, elephant, deer etc. had roamed the planet before going extinct. Though his discover may seem trivial today, Cuvier’s suggestion was an absolute paradigm shift. By demonstrating that long-lost species of animals had once roamed the earth possibly tens of thousands of years in the past, Cuvier had challenged the conventionally accepted Creationist worldview which purported that the earth was only several thousands of years old, and that all the planet’s creatures had been present since Creation. Cuvier further complicated the traditional worldview when in 1824, he named and described several hitherto unknown fossil species found in the Maestricht fossil beds: ichthyosaurus, a fish-like marine reptile; mosasaurus, a large crocodilian marine reptile and pterodactyl, a species of birdlike flying lizards. Plesiosaurus, a large predatory marine reptile notable for its small head atop a long serpentine neck was also discovered in that year, and as I will describe below, provided the visual template for lake monsters such as the Loch Ness Monster. These discoveries laid the ground for a profoundly new conception of historical time: that the earth and the organisms that inhabited it were not static but were subject to some sort of change, and that completely alien forms of life had preceded all kinds of currently existing plants and animals by thousands of years.

Thank you so much for this brilliant and fascinating thread! Truly a scintillating gem.