Like many others in society, I’m a massive fantasy nerd and I adore any movie, book, TV show, video game or tabletop RPG related to the fantasy genre. One of the main features of any mainstream fantasy representation is dragons, and who wouldn’t want dragons in their fantasy world! Giant winged lizards, which fly around the sky, breathing fire and demolishing any puny humanoids in their path, but is that image scientifically accurate?
Let’s first look at the whole concept of a dragon breathing fire. First off, the concept itself does exist in a similar way in the real world. The bombardier beetle uses the boiling hot by-products of the chemical reactions in its abdomen as a defence mechanism by shooting it at threats, thus incredibly similar to breathing fire. However, for combustion to occur, three things are required: oxygen, fuel and heat. Oxygen is pretty simple for a dragon as it just gets the oxygen from the air when breathing in. The heat and fuel sources for dragon breath are inextricably linked to the dragon’s digestive system and eating patterns.
The bombardier beetle uses the boiling hot by-products of the chemical reactions in its abdomen as a defence mechanism by shooting it at threats, thus incredibly similar to breathing fire
Dragons, although rarely depicted in modern representations this way, are historically omnivores meaning they eat both meat and vegetation. Dragons would be large in size due to the required wingspan to allow them to fly and this would mean that they could swallow large livestock or even humans whole. This provides a digestive problem for dragons because the bones of its food can’t be broken down inside the body. This is where some theorise that dragons also swallow stones or rocks in order to grind down the bones inside their stomach, making it easier to digest much in the same way that a lot of birds do in the real world. Before swallowing the rocks, they would first be ground down by the dragon’s teeth and this is the critical part that allows the dragon to breathe fire.
There are two prevailing theories at this point that explain how dragons breathe fire. The first comes from Anne McCafferey, the author of the long-running science fiction book series Pern, who argues that the grinding of rocks allows for the outer layer to be worn away and this means that when the rocks are swallowed, the stomach acid reacts with the rocks to produce phosphine gas which tends to self-ignite rather explosively when mixed with air. The other theory is that residue traces of metal from the rocks remain on the teeth and when the mixture of hydrogen and methane-based intestinal gases is expelled (basically when the dragon burps), the gases are ignited by the metal thus creating fire.
Dragons would be large in size due to the required wingspan to allow them to fly and this would mean that they could swallow large livestock or even humans whole
Until this point one of the major considerations about dragons has not been considered which is that dragons are reptiles and reptiles are cold-blooded. The cold-blooded nature of the dragons would mean that they are extremely reliant upon the sun for all basic bodily activities as well as its ability to fly for two reasons. Firstly, when a dragon is warmed by the sun, its body would heat up to higher temperatures from both the sun and the ‘fire-breath creating’ reactions inside the body. This would make the dragon weigh less because the air surrounding the dragon is less dense. Since the dragon’s volume doesn’t change and mass is equal to density multiplied by volume, heating the air and the dragon would decrease the mass of the dragon in the air. Imagine a hot-air balloon just dragon-shaped and propelled by wings rather than trapped air. The result would be that dragons could take flight if heated by the sun because less energy is required to push the dragon into the sky because it weighs less.
However, the downside to this is that as the dragon gets higher the more energy is required and the less effective the wings get at gaining altitude due to cooler air resulting in higher density and summarily higher mass. Simply put dragons need sunlight to take-off, so sorry Toothless no midnight flights for you. The other reason why sunlight is needed for flight is the energy requirement. Dragons need to hunt and consume large amounts of livestock or other sources of food to provide the energy to move and fly, stemming from their colossal size. However as established earlier, dragons can only fly during the daytime and since dragons wouldn’t get enough prey by not flying because their size would scare off food from miles away. Since dragons need the sun to fly, to fly to hunt and need to hunt to survive, dragons need sunlight to survive. This would mean that the whole concepts of dragons living in caves or mountains from movies or books are simply not accurate scientifically speaking.
The cold-blooded nature of the dragons would mean that they are extremely reliant upon the sun for all basic bodily activities as well as its ability to fly for two reasons
All in all, this brings up the final factor, which leads to the extinction of the dragons in the real world. The ecological limitations upon the dragon’s food chain would most likely lead to its extinction far faster than any other factor. The amount of energy required to hunt the animals as well as the limited time frame in which to do so limits large dragons food sources to large creatures, such as mammoths, which wouldn’t reproduce quick enough to sustain a dragon population indefinitely. Anything smaller would provide a net loss of energy in terms of energy required to hunt it versus energy gained from consuming it. This is the sad truth about dragons and although arguably smaller dragons could be sustained, without its size, the characteristic that makes a dragon iconic, its fire breath, would exist in the smaller versions. So regretfully the majestic dragon will always remain what it was originally created to be, a fantasy in the minds of millions.