The Biology of Dragons
Sorry, Tohru, that is not how it works. That is not how any of this works. Dragons are actually very interesting mythological creatures which are shared between a number of different ancient cultures across Eurasia. There are two basic types of dragons, the classic European dragon Western cultures are more familiar with, and the Asian dragon. The European dragon is typically shown to have animal level intelligence, so Tohru must be the Einstein of dragons.
Asian dragons, on the other hand, are often depicted as having above average intelligence, and are much more snake-like in appearance.
Despite some obvious differences, there are also several commonalities between all dragons that can be used to create a stereotypical dragon that might be possible biologically: 1- Size, 2- Fire breathing, 3- Crave shiny things, 4- Fly
Dragons are large reptilian beasts and think humans are crunchy and taste good with barbeque sauce. Dragons come in a large range of sizes, but most are considerably larger than humans and other animals. The largest reptile in the world today is the salt water crocodile, 6m long and 1,000kg in weight, but it pales in comparison to most dragons.
Dinosaurs on the other hand were much, much larger with the largest on record being the titanosaur Argentinosaurus huinculensis at 22-26 meter long, weighing in at 60-88 tons.
Some of you might be thinking, but then why aren’t there any extremely large reptiles alive today? The answer to that is the environment. Traditionally it was thought that the level of oxygen in the prehistoric atmosphere was much higher than it is today. The higher level of oxygen made it easier for the animals to reach a larger size due to how oxygen would interact with the dinosaurs on a cellular level. Recently studies have shown this not to be the case, as it turns out that there is more oxygen in the atmosphere today than there was during the prehistoric eras. Either way, the lack of large reptiles is linked to a difference in the environment.
2- Breathe Fire
Dragons can breathe fire, which gives them the ability to create instant barbeque, and it is something that no other living organism can do. While no organism currently breathes fire, there possibly is a way for organisms to breathe fire if the right biological systems are combined. There are many biologically created compounds that are flammable in the right conditions, such as methane and other hydrocarbons. These would make excellent fuel sources for generating raging fireballs, but in the case of dragons hydrogen is the best choice. When the hydrogen combines with oxygen and a spark is produced, water is created in the ensuing reaction.
2H2(g) + O2(g) → 2H2O(g)
The next step is to have the dragon produce and store hydrogen inside its body. Bacteria are a rather diverse group of unicellular organisms that have some unique metabolisms. The following bacteria create hydrogen as a waste product: Clostridium, Desulfovibrio, Ralstonia, and the pathogens Helicobacter and E. coli. The last two, Helicobacter and E. Coli, can live inside of other living organisms. The dragon just needs to be immune to the negative effects, similar to how we are immune to the normal bacteria that live in the human intestinal tract.
The next logical question then is where will the bacteria live and where will the hydrogen be stored? I first thought it would be in a structure similar to the swim bladder of a fish. The swim bladder is located inside the body of the fish and it holds gas.
The swim bladder is used to regulate the buoyancy of a fish, allowing it to float up and down in the water with minimal effort. This is all well and good, but the problem with the swim bladder is that it will slowly evolve over time, becoming the lungs in terrestrial animals. A better choice would be the air sacs of birds, as birds are now classified as a subgroup of reptiles. This was mentioned to me after giving this as part of my Biology of Dragons and Monster Girls panel at Otakon 2017. Air sacs are a unique part of the avian respiratory system that allows for the air to pass through the system in one direction, which means that there is no dead space or air that remains permanently trapped in the system. Humans have a different system where some air remains in the lungs even when we breathe out as deeply as possible, and this is referred to as the residual volume. This air is mixed with fresh air every time we breathe in lowering the efficiency of the system. Air sacs prevent this mixing and the air remains fresh as it travels through the lungs. FYI- they are not involved in gas exchange and do not function as lungs
Dinosaurs are also currently thought to have had air sacs, so it’s not a big stretch to think that our stereotypical dragon might also have air sacs. These air sacs would be the perfect location for hydrogen producing bacteria to live and produce hydrogen. This way the dragon would have an easy way to expel hydrogen with a breath, creating a highly volatile hydrogen/ oxygen mix. This mix when ignited would create a fireball. Most birds have 9 air sacs and dragons would probably have around the same number, and by having multiple air sacs filled with hydrogen dragons would be able to regulate the size and intensity of the fireball by controlling the number of air sacs that it expels with each breath.
The last piece of the puzzle is igniting the hydrogen/ oxygen mix to finally create fire. This means that the dragon has to be able to create a spark to ignite the hydrogen/ oxygen mix coming out of its lungs. First things first, the dragon cannot create the fire inside any part of its body because fire and explosions are bad unless you want barbequed dragon. Therefore, the best location for the dragon fire ignition point is on the large teeth at the front of the mouth.
By using the teeth as the ignition point the fire will be leaving the mouth, preventing the dragon from cooking its own mouth. The teeth also provide a useful structure for creating the actual spark.
The teeth of a dragon could also function as biological spark plugs by using platinum, which acts as a catalyst for a hydrogen/ oxygen reaction, and it can conduct electricity. The electricity would be generated by modified muscles much like how an electric eel does. The electricity is then transferred across the platinum electrodes on the teeth igniting the hydrogen and oxygen, creating fire.
3- Crave shiny things
Dragons, especially in the Western myths, crave shiny things, and dragons need platinum in order to breathe fire. Platinum is a metal and this metal just so happen to be shiny, especially platinum even in its natural state.
Thus, dragons craving shiny things is how they locate the platinum needed for their teeth. At this point you’re probably wondering just how much platinum do dragons need once their teeth are grown? Unlike humans and mammals, which are diphyodont (growing only 2 sets of teeth 1 child, 1 adult), most other vertebrates are polyphyodont. This includes reptiles, so they will constantly regrow teeth as they are lost. That means then that dragons need a constant source of platinum to retain their fire breathing ability as they regrow lost teeth.
Yes, there were dinosaurs that could fly and glide, but dragons are big and heavy with tiny wings relative to their size. So, the question remains just how the heck are they able to fly? The answer goes back to why I picked hydrogen as the fuel source for the dragon’s ability to breathe fire. Except for methane, all other hydrocarbons are heavier than air. So, while methane and hydrogen can both be used to generate fire, hydrogen is still the better choice as it has a better lift capacity (it’s much lighter than air than methane), because dragons are part blimp. The hydrogen stored in the dragon’s air sacs effectively lowers the dragon’s weight to the point that the smaller wings can generate enough lift, allowing the dragon to fly. The downside to this is that if the dragon uses to much of its hydrogen creating fire, it will not be able to fly until the hydrogen is replenished.
A discussion on lift can be found here.
While dragons do not exist, there are biological systems and structures that, when combined, could allow a dragon-like creature to exist. The ability to turn into a sexy maid, not so much.