Dragons Were Actually Just Snakes
What we now know of as dragons pretty much didn’t exist in Western mythology. Perhaps the “fire drake” in Beowulf was the only such dragon.
What did exist were serpents, and those serpents became more dragon-like as time went on.
According to Alan Brown:
For so well known a creature, the occidental dragon has had a surprising number of mutations during its literary history. The original [dragon], an everyday snake, evolved rapidly into the venomous, ruin-inhabiting serpent par excellence, which then acquired the impressive trait of flight from Arabian winged serpents mentioned by Herodotus, and a scientific justification for its extreme size from Indian and African constrictors described by Pliny the Elder. Even the quite inconsistent feature of legs (two or even four of them) which crept in, so to speak, much later on, can presumably be attributed to medieval illustrators for whom a serpent was a beast much like any other, that is, looking a good deal like a dog…
Still it sometimes comes as a surprise to moderns to learn that what Goldsmith calls the “large feature” of fiery breath is closely associated with the dragon of European tradition can be traced back no further than to early Insular literature, notably the Old English Beowulf.
Greek mythology supposedly had dragons, but they were serpents. The word “draco” is supposedly Latin for “dragon” and there is a Draco constellation that represents a serpent from ancient Greek mythology—a serpent called “Ladon” or “Landon.” Ladon was a guardian of a garden with trees growing apples that turn people immortal. (There is a similar tree, serpent, and garden in the Bible.)
Additionally, the word “dragon” originated from the ancient Greek word “drakon,” which literally meant “snake” or “serpent.”
Norse mythology also had at least one dragon that might be more than a serpent—“Fafnir” who was known to guard his collection of treasure. However, Fafnir did not have fire breath or wings.